3580 lines
138 KiB
HTML
3580 lines
138 KiB
HTML
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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
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<html>
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<head>
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<title>Mini GLX Specification</title>
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</head>
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<body>
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<span style="font-style: italic;"></span><span
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style="font-weight: bold;"></span>
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<h1>
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<center>Mesa Subset Specification</center>
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</h1>
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<h2>
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<center>
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<h3>Tungsten Graphics, Inc.</h3>
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<h3>February 26, 2003<br>
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</h3>
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</center>
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</h2>
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<p> Copyright © 2002-2003 by <a
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href="http://www.tungstengraphics.com/">Tungsten Graphics, Inc.</a>,
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Cedar Park, Texas. All Rights Reserved. <br>
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<br>
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Permission is granted to make and distribute verbatim copies of this
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document provided the copyright notice and this permission notice are
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preserved on all copies.<br>
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</p>
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<p> OpenGL is a trademark of <a href="http://www.sgi.com">Silicon
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Graphics, Inc.</a>.</p>
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<h1>1. Introduction</h1>
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This document describes a subset of the Mesa implemented by Tungsten
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Graphics, Inc. for embedded devices. Prior to reading this
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document the reader should be familiar with the OpenGL 1.2.1
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specification dated April 1, 1999 (available from <a
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href="http://www.opengl.org/developers/documentation/specs.html">http://www.opengl.org/developers/documentation/specs.html</a>.)
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Experience with OpenGL programming is highly advisable.<a
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href="http://www.opengl.org/developers/documentation/specs.html"><br>
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</a><br>
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Tungsten Graphics, Inc. is working with industry standards
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organizations +in an attempt to standardize this Mesa subset and any
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other possible subsets +as a result of this work. <br>
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<br>
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Appendix A contains a list of issues of which some may not be resolved.<br>
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<br>
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To summarize, the following major features of Mesa are omitted from the
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subset:<br>
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<ul>
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<li>Vertex arrays</li>
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<li>Texture coordinate generation</li>
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<li>Lighting</li>
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<li>Point size</li>
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<li>Polygon stipple</li>
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<li>DrawPixels, CopyPixels, PixelZoom</li>
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<li>1-D and 3-D textures</li>
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<li>CopyTex[Sub]Image</li>
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<li>Fog</li>
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<li>Depth test</li>
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<li>Color Index mode</li>
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<li>Accumulation buffer</li>
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<li>Feedback mode</li>
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<li>Evaluators</li>
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<li>Push/Pop attributes</li>
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<li>Display lists<br>
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</li>
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</ul>
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<p>Further reductions are made at a lower level of detail.<br>
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</p>
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<p>Mesa function names are printed in <span style="font-weight: bold;">bold
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face</span>. Function parameters are printed in <span
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style="font-style: italic;">italics</span>.<br>
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</p>
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<p>The Tungsten Graphics, Inc. Mesa subset library is hereafter
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referred to as <span style="font-style: italic;">the subset.</span><br>
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<br>
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</p>
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<h1>2. Primitive Specification</h1>
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<h2>2.1 glBegin, glEnd and glVertex Commands</h2>
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The basic rendering primitives are points, lines and triangles.
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Quadrilaterals and polygons are composed of triangles.
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Primitives are drawn with the <span style="font-weight: bold;">glBegin</span>
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and <span style="font-weight: bold;">glEnd</span> commands and a subset
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of the <span style="font-weight: bold;">glVertex</span> commands:<br>
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<br>
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<div style="margin-left: 40px;">void <span style="font-weight: bold;">glBegin</span>(GLenum<span
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style="font-style: italic;">mode</span>)<br>
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void <span style="font-weight: bold;">glEnd</span>(void)<br>
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<br>
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void <span style="font-weight: bold;">glVertex2f</span>(GLfloat <span
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style="font-style: italic;">x</span>, GLfloat <span
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style="font-style: italic;">y</span>)<br>
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void <span style="font-weight: bold;">glVertex2fv</span>(const GLfloat
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*<span style="font-style: italic;">v</span>)<br>
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void <span style="font-weight: bold;">glVertex3f</span>(GLfloat <span
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style="font-style: italic;">x</span>, GLfloat <span
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style="font-style: italic;">y</span>, GLfloat <span
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style="font-style: italic;">z</span>)<br>
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void <span style="font-weight: bold;">glVertex3fv</span>(const GLfloat
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*<span style="font-style: italic;">v</span>)<br>
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</div>
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<br>
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The <span style="font-style: italic;">mode</span> parameter to <span
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style="font-weight: bold;">glBegin</span> may be one of the following<br>
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<br>
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<div style="margin-left: 40px;">GL_POINTS - a series of individual
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points<br>
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GL_LINES - a series of disjoint line segments<br>
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GL_LINE_STRIP - series of connected line segments<br>
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GL_LINE_LOOP - a closed loop of line segments<br>
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GL_TRIANGLES - a series of individual triangles<br>
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GL_TRIANGLE_STRIP - a connected strip of triangles<br>
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GL_TRIANGLE_FAN - a sequence of triangles all sharing a common vertex<br>
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GL_QUADS - a sequence of individual quadrilaterals<br>
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GL_QUAD_STRIP - a connected strip of quadrilaterals<br>
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GL_POLYGON - a closed, convex polygon<br>
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<br>
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</div>
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<br>
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The <span style="font-weight: bold;">glVertex</span> commands take two
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or three floating point coordinates, or a pointer to an array of two or
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three floating point coordinates. Vertices are actually 4-element
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homogeneous coordinates. The fourth component, unspecified by the
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subset's <span style="font-weight: bold;">glVertex</span> commands, is
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one.<br>
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<br>
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<span style="font-weight: bold;"></span>
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<h2>2.2 Other Per-vertex Commands<br>
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</h2>
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The <span style="font-weight: bold;">glColor</span> and <span
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style="font-weight: bold;">glTexCoord</span> commands may be used to
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specify colors and texture coordinates for each vertex:<br>
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<br>
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<div style="margin-left: 40px;">void <span style="font-weight: bold;">glColor3f</span>(GLfloat<span
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style="font-style: italic;">red</span>, GLfloat <span
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style="font-style: italic;">green</span>, GLfloat <span
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style="font-style: italic;">blue</span>)<br>
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void <span style="font-weight: bold;">glColor3fv</span>(const GLfloat *<span
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style="font-style: italic;">rgb</span>)<br>
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void <span style="font-weight: bold;">glColor4f</span>(GLfloat <span
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style="font-style: italic;">red,</span> GLfloat <span
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style="font-style: italic;">green,</span> GLfloat <span
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style="font-style: italic;">blue,</span> GLfloat <span
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style="font-style: italic;">alpha</span>)<br>
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void <span style="font-weight: bold;">glColor4fv</span>(const GLfloat *<span
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style="font-style: italic;">rgba</span>)<br>
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void <span style="font-weight: bold;">glTexCoord2f</span>(GLfloat <span
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style="font-style: italic;">s</span>, GLfloat<span
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style="font-style: italic;"> t</span>)<br>
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void <span style="font-weight: bold;">glTexCoord2fv</span>(const
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GLfloat *<span style="font-style: italic;">c</span>)<br>
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<br>
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</div>
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The <span style="font-weight: bold;">glColor</span> commands specify
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the color and optionally, the alpha value, for subsequent vertices.
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For the <span style="font-weight: bold;">glColor3</span> commands,
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alpha is set to one.<br>
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<br>
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The <span style="font-weight: bold;">glTexCoord2</span> commands
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specify the texture coordinate for subsequent vertices. Texture
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coordinates are actually four-component coordinates: (s, t, r, q).
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The <span style="font-weight: bold;">glTexCoord2</span> commands
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set s and t explicitly. The r and q components are zero and one,
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respectively.<br>
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<br>
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<span style="font-weight: bold;"></span>Only <span
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style="font-weight: bold;">glVertex, glColor</span> and <span
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style="font-weight: bold;">glTexCoord</span> commands are allowed
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between <span style="font-weight: bold;">glBegin</span> and <span
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style="font-weight: bold;">glEnd.</span> Calling any other
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command between <span style="font-weight: bold;">glBegin</span> and <span
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style="font-weight: bold;">glEnd</span> will result in the error
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GL_INVALID_OPERATION.<br>
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<br>
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<h2>2.3 Unsupported Commands</h2>
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None of the following commands related to primitive specification are
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supported by the subset:<br>
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<br>
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<div style="margin-left: 40px;">Per-Vertex commands:<br>
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</div>
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<div style="margin-left: 40px;">
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<div style="margin-left: 40px;"><span style="font-weight: bold;">glVertex2d,
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glVertex2i, glVertex2s, glVertex3d, glVertex3i, glVertex3s, glVertex4d,
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glVertex4i, glVertex4s, glVertex2dv, glVertex2iv, glVertex2sv,
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glVertex3dv, glVertex3iv, glVertex3sv, glVertex4dv, glVertex4iv,
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glVertex4sv,<br>
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glNormal3b, glNormal3d, glNormal3f, glNormal3i, glNormal3s, </span><span
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style="font-weight: bold;">glNormal3bv, glNormal3dv, glNormal3fv,
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glNormal3iv, glNormal3sv,<br>
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glIndexd, glIndexf, glIndexi, glIndexs, glIndexub, glIndexdv,
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glIndexfv, glIndexiv, glIndexsv, glIndexubv,<br>
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glColor3b, glColor3d, glColor3i, glColor3s, glColor3ub, glColor3ui,
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glColor3us, </span><span style="font-weight: bold;">glColor3bv,
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glColor3dv, glColor3iv, glColor3sv, glColor3ubv, glColor3uiv,
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glColor3usv,</span><span style="font-weight: bold;"> lColor4b,
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glColor4d, glColor4i, glColor4s, glColor4ub, glColor4ui, glColor4us, </span><span
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style="font-weight: bold;">glColor4bv, glColor4dv, glColor4iv,
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glColor4sv, glColor4ubv, glColor4uiv, glColor4usv,<br>
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</span><span style="font-weight: bold;">glTexCoord1d, glTexCoord1f,
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glTexCoord1i, glTexCoord1s, glTexCoord2d, glTexCoord2i, glTexCoord2s,
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glTexCoord3d, glTexCoord3f, glTexCoord3i, glTexCoord3s, glTexCoord4d,
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glTexCoord4f, glTexCoord4i, glTexCoord4s, glTexCoord1dv, glTexCoord1fv,
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glTexCoord1iv, glTexCoord1sv, glTexCoord2dv, glTexCoord2iv,
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glTexCoord2sv, glTexCoord3dv, glTexCoord3fv, glTexCoord3iv,
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glTexCoord3sv, glTexCoord4dv, glTexCoord4fv, glTexCoord4iv,
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glTexCoord4sv,<br>
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glEdgeFlag, glEdgeFlagv</span><br style="font-weight: bold;">
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<br>
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</div>
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Vertex array commands:<br>
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<div style="margin-left: 40px;"><span style="font-weight: bold;">glVertexPointer,
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glColorPointer, glIndexPointer, glTexCoordPointer, glEdgeFlagPointer,
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glNormalPointer, glInterleavedArrays, glArrayElement, glDrawArrays,
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glDrawElements, glDrawRangeElements, glEnableClientState,
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glDisableClientState</span><br>
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</div>
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</div>
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<div style="margin-left: 40px;"><br>
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Rectangle commands:<br>
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<div style="margin-left: 40px;"><span style="font-weight: bold;">glRects,
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glRecti, glRectf, glRectd, glRectsv, glRectiv, glRectfv, glRectdv,<br>
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<br>
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</span></div>
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</div>
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<div style="margin-left: 40px;">Lighting commands:<br>
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</div>
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<div style="margin-left: 80px;"><span style="font-weight: bold;">glMaterialf,
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glMateriali, glMaterialfv, glMaterialiv<br>
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</span><br>
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</div>
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<div style="margin-left: 40px;"> Evaluator commands:<br>
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<div style="margin-left: 40px;"><span style="font-weight: bold;">glEvalCoord1d,
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glEvalCoord1f, glEvalCoord1dv, glEvalCoord1fv, </span><span
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style="font-weight: bold;">glEvalCoord2d, glEvalCoord2f,
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glEvalCoord2dv, glEvalCoord2fv,<br>
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</span><span style="font-weight: bold;">glEvalPoint1, glEvalPoint2</span><br>
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<br>
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</div>
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</div>
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<h1>3. Coordinate Transformation</h1>
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<h2>3.1 Vertex Transformation</h2>
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Vertex coordinates are transformed by the current modelview and
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projection matrices then mapped to window coordinates as specified by
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the viewport. The following coordinate transformation commands are
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supported by the subset<br>
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<br>
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<div style="margin-left: 40px; font-weight: bold;">glMatrixMode<span
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style="font-weight: normal;">(GLenum <span style="font-style: italic;">mode</span>)</span><br>
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glLoadIdentity<span style="font-weight: normal;">(void)</span><br>
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glPushMatrix<span style="font-weight: normal;">(void)</span><br>
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glPopMatrix<span style="font-weight: normal;">(void)</span><br>
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glLoadMatrixf<span style="font-weight: normal;">(const GLfloat *<span
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style="font-style: italic;">m</span>)</span><br>
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glMultMatrixf<span style="font-weight: normal;">(const GLfloat *<span
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style="font-style: italic;">m</span>)</span><br>
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glRotatef<span style="font-weight: normal;">(GLfloat <span
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style="font-style: italic;">angle</span>, GLfloat <span
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style="font-style: italic;">x</span>, GLfloat <span
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style="font-style: italic;">y</span>, GLfloat <span
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style="font-style: italic;">z</span>)</span><br>
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glTranslatef<span style="font-weight: normal;">(GLfloat <span
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style="font-style: italic;">x</span>, GLfloat <span
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style="font-style: italic;">y</span>, GLfloat <span
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style="font-style: italic;">z</span>)</span><br>
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glScalef<span style="font-weight: normal;">(GLfloat <span
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style="font-style: italic;">x</span>, GLfloat <span
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style="font-style: italic;">y</span>, GLfloat <span
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style="font-style: italic;">z</span>)<br>
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<span style="font-weight: bold;">glFrustum(</span>GLdouble <span
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style="font-style: italic;">left,</span> GLdouble <span
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style="font-style: italic;">right,</span> GLdouble <span
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style="font-style: italic;">bottom,</span> GLdouble <span
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style="font-style: italic;">top,</span> GLdouble <span
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style="font-style: italic;">near,</span> GLdouble <span
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style="font-style: italic;">far</span>)</span><br>
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<span style="font-weight: normal;"><span style="font-weight: bold;">glOrtho(</span>GLdouble<span
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style="font-style: italic;"> left,</span> GLdouble <span
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style="font-style: italic;">right,</span> GLdouble <span
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style="font-style: italic;">bottom,</span> GLdouble <span
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style="font-style: italic;">top,</span> GLdouble <span
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style="font-style: italic;">near,</span> GLdouble <span
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style="font-style: italic;">far</span>)</span><br>
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glViewport<span style="font-weight: normal;">(GLint <span
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style="font-style: italic;">x</span>, GLint <span
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style="font-style: italic;">y</span>, GLsize <span
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style="font-style: italic;">width,</span> GLsizei <span
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style="font-style: italic;">height</span>)</span><br>
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</div>
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<br>
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||
|
|
The <span style="font-weight: bold;">glMatrixMode</span> command
|
||
|
|
specifies the <span style="font-style: italic;">current matrix.</span>
|
||
|
|
The mode parameter may be GL_MODELVIEW or GL_PROJECTION to specify
|
||
|
|
the modelview matrix or projection matrix. Subsequent matrix
|
||
|
|
commands will effect the current matrix. Also associated with the
|
||
|
|
modelview and projection matrices are a modelview matrix stack and
|
||
|
|
projection matrix stack.<br>
|
||
|
|
<br>
|
||
|
|
The <span style="font-weight: bold;">glLoadIdentity</span> command
|
||
|
|
replaces the current matrix with the identity matrix. The matrix
|
||
|
|
elements are specified in column-major order.<br>
|
||
|
|
<br>
|
||
|
|
The <span style="font-weight: bold;">glPushMatrix</span> command pushes
|
||
|
|
a copy of the current matrix onto either the modelview matrix stack or
|
||
|
|
the projection matrix stack. The <span style="font-weight: bold;">glPopMatrix</span>
|
||
|
|
command replaces the current matrix with a copy of the top matrix off
|
||
|
|
the modelview matrix stack or projection matrix stack, the pops the
|
||
|
|
stack. Matrix stacks are useful for traversing and rendering
|
||
|
|
hierarchical models.<br>
|
||
|
|
<br>
|
||
|
|
The <span style="font-weight: bold;">glMultMatrixf</span> command
|
||
|
|
post-multiplies the current matrix by the specified matrix. The
|
||
|
|
matrix elements are specified in column-major order.<br>
|
||
|
|
<br>
|
||
|
|
The <span style="font-weight: bold;">glRotatef</span> command
|
||
|
|
post-multiplies the current matrix by a rotation matrix defined by the
|
||
|
|
angle and rotation axis defined by x, y and z.<br>
|
||
|
|
<br>
|
||
|
|
The <span style="font-weight: bold;">glTranslatef</span> command
|
||
|
|
post-multiplies the current matrix by a translation matrix defined by
|
||
|
|
the <span style="font-style: italic;">x</span>, <span
|
||
|
|
style="font-style: italic;">y</span> and <span
|
||
|
|
style="font-style: italic;">z</span> translation parameters.<br>
|
||
|
|
<span style="font-weight: bold;"></span><br>
|
||
|
|
The <span style="font-weight: bold;">glScalef</span> command
|
||
|
|
post-multiplies the current matrix by a scaling matrix defined by the <span
|
||
|
|
style="font-style: italic;">x</span>, <span
|
||
|
|
style="font-style: italic;">y</span> and <span
|
||
|
|
style="font-style: italic;">z</span> scale factors.<br>
|
||
|
|
<span style="font-weight: bold;"></span><br>
|
||
|
|
The <span style="font-weight: bold;">glFrustum</span> command
|
||
|
|
post-multiplies the current matrix by a perspective projection matrix.
|
||
|
|
The <span style="font-style: italic;">near</span> and <span
|
||
|
|
style="font-style: italic;">far</span> values specify the position of
|
||
|
|
the hither and yon Z-axis clipping planes. The <span
|
||
|
|
style="font-style: italic;">left, right, bottom</span> and <span
|
||
|
|
style="font-style: italic;">top</span> parameters are the X and Y
|
||
|
|
extents at the near clipping plane. <span
|
||
|
|
style="font-weight: bold;">glFrustum</span> is normally used to modify
|
||
|
|
the projection matrix.<br>
|
||
|
|
<br>
|
||
|
|
The <span style="font-weight: bold;">glOrtho</span> command
|
||
|
|
post-multiplies the current matrix by an orthographic projection matrix.
|
||
|
|
The <span style="font-style: italic;">near</span> and <span
|
||
|
|
style="font-style: italic;">far</span> values specify the position of
|
||
|
|
the hither and yon Z-axis clipping planes. The <span
|
||
|
|
style="font-style: italic;">left, right, bottom</span> and <span
|
||
|
|
style="font-style: italic;">top</span> parameters specify the X and
|
||
|
|
Y-axis clipping planes. <span style="font-weight: bold;">glOrtho</span>
|
||
|
|
is normally used to modify the projection matrix.<br>
|
||
|
|
<br>
|
||
|
|
The <span style="font-weight: bold;">glViewport</span> command
|
||
|
|
specifies the mapping of coordinates from normalized device coordinates
|
||
|
|
to window coordinates. The <span style="font-style: italic;">x</span>
|
||
|
|
and <span style="font-style: italic;">y</span> parameters specify the
|
||
|
|
viewport's lower-left corner in the window and the <span
|
||
|
|
style="font-style: italic;">width</span> and <span
|
||
|
|
style="font-style: italic;">height</span> parameters specify the size
|
||
|
|
of the viewport. <span style="font-weight: bold;">glViewport</span>
|
||
|
|
does not effect the current matrix.<br>
|
||
|
|
<br>
|
||
|
|
A coordinate transformed to window coordinates is hereafter known as (x<sub>w</sub>,
|
||
|
|
y<sub>w</sub>, z<sub>w</sub>).<br>
|
||
|
|
<br>
|
||
|
|
<h2>3.2 Clipping</h2>
|
||
|
|
View-volume clipping automatically discards or trims primitives which
|
||
|
|
lie completely or partially outside of the view volume specified by <span
|
||
|
|
style="font-weight: bold;">glFrustum</span> and <span
|
||
|
|
style="font-weight: bold;">glOrtho</span>. Note that the <span
|
||
|
|
style="font-weight: bold;">glViewport</span> command does not define a
|
||
|
|
clipping region.<br>
|
||
|
|
<br>
|
||
|
|
Clipping occurs in <span style="font-style: italic;">clip coordinate
|
||
|
|
space - </span>the coordinates produced after applying the projection
|
||
|
|
matrix.<br>
|
||
|
|
<br>
|
||
|
|
<h2>3.3 Current Raster Position</h2>
|
||
|
|
The current raster position specifies the location for drawing images
|
||
|
|
with <span style="font-weight: bold;">glBitmap.</span> The current
|
||
|
|
raster position is set with the commands:<br>
|
||
|
|
<br>
|
||
|
|
<div style="margin-left: 40px;">void <span style="font-weight: bold;">glRasterPos2f</span>(GLfloat<span
|
||
|
|
style="font-style: italic;">x</span>, GLfloat <span
|
||
|
|
style="font-style: italic;">y</span>)<br>
|
||
|
|
void <span style="font-weight: bold;">glRasterPos2fv</span>(const
|
||
|
|
GLfloat *<span style="font-style: italic;">v</span>)<br>
|
||
|
|
void <span style="font-weight: bold;">glRasterPos2i</span>(GLint <span
|
||
|
|
style="font-style: italic;">x</span>, GLint <span
|
||
|
|
style="font-style: italic;">y</span>)<br>
|
||
|
|
void <span style="font-weight: bold;">glRasterPos2iv</span>(const
|
||
|
|
GLint *<span style="font-style: italic;">v</span>)<br>
|
||
|
|
</div>
|
||
|
|
<br>
|
||
|
|
<span style="font-weight: bold;">glRasterPos</span> specifies a
|
||
|
|
4-component coordinate (x, y, 0, 1). The coordinate is processed
|
||
|
|
like a vertex; it is transformed by the modelview matrix, the projection
|
||
|
|
matrix and mapped to the viewport. The resulting window coordinate
|
||
|
|
is stored as the current raster position. The coordinate is
|
||
|
|
clipped-tested against the frustum like a vertex. If the
|
||
|
|
coordinate is clipped, then the current raster position becomes invalid
|
||
|
|
and subsequent <span style="font-weight: bold;">glBitmap</span> commands
|
||
|
|
have no effect.<br>
|
||
|
|
<br>
|
||
|
|
<span style="font-weight: bold;">glRasterPos</span> also updates the
|
||
|
|
current raster color and current raster texture coordinates. The
|
||
|
|
current raster color is updated (copied) from the current color (as
|
||
|
|
specified by <span style="font-weight: bold;">glColor</span>).
|
||
|
|
The current raster texture coordinate is updated (copied) from the
|
||
|
|
current texture coordinate (as specified by <span
|
||
|
|
style="font-weight: bold;">glTexCoord</span>).<br>
|
||
|
|
<br>
|
||
|
|
<h2>3.4 Unsupported Commands</h2>
|
||
|
|
The following commands related to vertex transformation are not
|
||
|
|
supported by the subset:<br>
|
||
|
|
<br>
|
||
|
|
<div style="margin-left: 40px;">User-defined clip plane commands:<br>
|
||
|
|
<div style="margin-left: 40px;"><span style="font-weight: bold;">glClipPlane</span><br>
|
||
|
|
</div>
|
||
|
|
<span style="font-weight: bold;"></span></div>
|
||
|
|
<br>
|
||
|
|
<div style="margin-left: 40px;">Lighting and material commands:</div>
|
||
|
|
<div style="margin-left: 80px;"><span style="font-weight: bold;">glLightModeli,
|
||
|
|
glLightModelf, </span><span style="font-weight: bold;">glLightModeliv,
|
||
|
|
glLightModelfv,</span><span style="font-weight: bold;"> glLightf,
|
||
|
|
glLighti, glLightfv, glLightiv, glColorMaterial</span><br>
|
||
|
|
</div>
|
||
|
|
<br>
|
||
|
|
<div style="margin-left: 40px;">Automatic texture coordinate generation
|
||
|
|
commands:<br>
|
||
|
|
</div>
|
||
|
|
<div style="margin-left: 40px;">
|
||
|
|
<div style="margin-left: 40px;"><span style="font-weight: bold;">glTexGend,
|
||
|
|
glTexGenf, glTexGeni, </span><span style="font-weight: bold;">glTexGendv,
|
||
|
|
glTexGenfv, glTexGeniv, </span><br>
|
||
|
|
<br style="font-weight: bold;">
|
||
|
|
</div>
|
||
|
|
Double-valued commands:<br>
|
||
|
|
<div style="margin-left: 40px;"><span style="font-weight: bold;">glLoadMatrixd,
|
||
|
|
glMultMatrixd, glRotated, glTranslated, glScaled</span><br
|
||
|
|
style="font-weight: bold;">
|
||
|
|
</div>
|
||
|
|
<br>
|
||
|
|
Depth Range command:<br>
|
||
|
|
<div style="margin-left: 40px;"><span style="font-weight: bold;">glDepthRange</span>
|
||
|
|
(the near value is always 0.0 and the far value is always 1.0)<br>
|
||
|
|
</div>
|
||
|
|
<br>
|
||
|
|
Extra RasterPos commands:<br>
|
||
|
|
<div style="margin-left: 40px;"><span style="font-weight: bold;">glRasterPos2d,
|
||
|
|
glRasterPos2s, glRasterPos3d, glRasterPos3f, glRasterPos3i,
|
||
|
|
glRasterPos3s, glRasterPos4d, glRasterPos4f, glRasterPos4i,
|
||
|
|
glRasterPos4s, glRasterPos2dv, glRasterPos2sv, glRasterPos3dv,
|
||
|
|
glRasterPos3fv, glRasterPos3iv, glRasterPos3sv, glRasterPos4dv,
|
||
|
|
glRasterPos4fv, glRasterPos4iv, glRasterPos4sv</span><br>
|
||
|
|
</div>
|
||
|
|
<br>
|
||
|
|
<br>
|
||
|
|
</div>
|
||
|
|
<h1>4. Rasterization</h1>
|
||
|
|
This section describes the commands and options for drawing points,
|
||
|
|
lines, triangles and bitmaps. <span style="font-style: italic;">Rasterization</span>
|
||
|
|
is the term for the process which produces fragments from the geometric
|
||
|
|
description of a primitive (a point, line, polygon or bitmap). For
|
||
|
|
example, given the two coordinates for the end-points of a line segment,
|
||
|
|
rasterization determines which pixels in the frame buffer are modified
|
||
|
|
to <span style="font-style: italic;">draw</span> the line. A
|
||
|
|
fragment is a tuple which consists of a window coordinate, colors and
|
||
|
|
texture coordinates. The fragments produced by rasterization are
|
||
|
|
subsequently processed by the per-fragment operations described later.<br>
|
||
|
|
<br>
|
||
|
|
<h2>4.1 Point Rasterization</h2>
|
||
|
|
Points are rendered with the command sequence <span
|
||
|
|
style="font-weight: bold;">glBegin</span>(GL_POINTS), <span
|
||
|
|
style="font-weight: bold;">glVertex</span>, ... <span
|
||
|
|
style="font-weight: bold;">glEnd</span>. The window coordinate (x<sub>w</sub>,
|
||
|
|
y<sub>w</sub>, z<sub>w</sub>) is truncated to rasterize the point.
|
||
|
|
The truncated coordinate with its associated color and texture
|
||
|
|
coordinate is sent as a single fragment to the per-fragment processing
|
||
|
|
stages.<br>
|
||
|
|
<br>
|
||
|
|
The <span style="font-weight: bold;">glPointSize</span> command is not
|
||
|
|
supported; only 1-pixel points are supported.<br>
|
||
|
|
<br>
|
||
|
|
Point smoothing (antialiasing) is also not supported.<br>
|
||
|
|
<br>
|
||
|
|
<h2>4.2 Line Rasterization</h2>
|
||
|
|
Lines are rendered with the command sequence <span
|
||
|
|
style="font-weight: bold;">glBegin</span>(<span
|
||
|
|
style="font-style: italic;">mode</span>), <span
|
||
|
|
style="font-weight: bold;">glVertex</span>, <span
|
||
|
|
style="font-weight: bold;">glVertex</span>, ... <span
|
||
|
|
style="font-weight: bold;">glEnd</span> where <span
|
||
|
|
style="font-style: italic;">mode</span> is one of GL_LINES,
|
||
|
|
GL_LINE_STRIP or GL_LINE_LOOP. Lines are rasterized as described
|
||
|
|
in the OpenGL specification. Note that OpenGL specifies the <span
|
||
|
|
style="font-style: italic;">half-open</span> convention for drawing
|
||
|
|
lines: the last fragment in a line segment is omitted so that endpoint
|
||
|
|
pixels shared by two line segments will only be drawn once instead of
|
||
|
|
twice.<br>
|
||
|
|
<br>
|
||
|
|
<h3>4.2.1 Line Width</h3>
|
||
|
|
The width of lines can be controlled by<br>
|
||
|
|
<br>
|
||
|
|
<div style="margin-left: 40px;">void <span style="font-weight: bold;">glLineWidth</span>(GLfloat<span
|
||
|
|
style="font-style: italic;">width</span>)<br>
|
||
|
|
</div>
|
||
|
|
<br>
|
||
|
|
where <span style="font-style: italic;">width</span> is the line width
|
||
|
|
in pixels. The width defaults to 1.0. Attempting to set the
|
||
|
|
width to a value less than or equal to zero will raise the error
|
||
|
|
GL_INVALID_VALUE.<br>
|
||
|
|
<br>
|
||
|
|
<h3>4.2.2 Line Stipple<br>
|
||
|
|
</h3>
|
||
|
|
Lines may be stippled (i.e. dashed) with the command<br>
|
||
|
|
<br>
|
||
|
|
<div style="margin-left: 40px;"><span style="font-weight: bold;">glLineStipple</span>(GLint<span
|
||
|
|
style="font-style: italic;">factor</span>, GLushort <span
|
||
|
|
style="font-style: italic;">pattern</span>)<br>
|
||
|
|
</div>
|
||
|
|
<br>
|
||
|
|
<span style="font-style: italic;">pattern</span> describes an on/off
|
||
|
|
pattern for the fragments produced by rasterization and <span
|
||
|
|
style="font-style: italic;">factor</span> specifies how many subsequent
|
||
|
|
fragments are kept or culled for each pattern bit. Line stippling
|
||
|
|
can be enabled or disabled by the commands <span
|
||
|
|
style="font-weight: bold;">glEnable</span>(GL_LINE_STIPPLE) and <span
|
||
|
|
style="font-weight: bold;">glDisable</span>(GL_LINE_STIPPLE).<br>
|
||
|
|
<br>
|
||
|
|
<h3>4.2.3 Line Antialiasing</h3>
|
||
|
|
Lines may be antialiased. For antialiased lines, each fragment
|
||
|
|
produced by rasterization is assigned a <span
|
||
|
|
style="font-style: italic;">coverage value</span> which describes how
|
||
|
|
much of the fragment's area is considered to be <span
|
||
|
|
style="font-style: italic;">inside</span> the line. Later, the
|
||
|
|
alpha value of each fragment is multiplied by the coverage value.
|
||
|
|
By blending the fragments into the frame buffer, the edges of
|
||
|
|
lines appear smoothed.<br>
|
||
|
|
<br>
|
||
|
|
Line antialiasing can be enabled or disabled with the commands <span
|
||
|
|
style="font-weight: bold;">glEnable</span>(GL_LINE_SMOOTH) and <span
|
||
|
|
style="font-weight: bold;">glDisable</span>(GL_LINE_SMOOTH).<br>
|
||
|
|
<br>
|
||
|
|
<h2>4.3 Polygon Rasterization</h2>
|
||
|
|
Polygons, quadrilaterals and triangles share the same polygon
|
||
|
|
rasterization options. <br>
|
||
|
|
<br>
|
||
|
|
Triangles are rendered by the command sequence <span
|
||
|
|
style="font-weight: bold;">glBegin</span><span
|
||
|
|
style="font-style: italic;"><span style="font-style: italic;">(mode</span></span>),<span
|
||
|
|
style="font-weight: bold;">glVertex</span>, <span
|
||
|
|
style="font-weight: bold;">glVertex</span>, ... <span
|
||
|
|
style="font-weight: bold;">glEnd</span> where <span
|
||
|
|
style="font-style: italic;">mode</span> may be one of GL_TRIANGLES,
|
||
|
|
GL_TRIANGLE_STRIP or GL_TRIANGLE_FAN.<span style="font-weight: bold;"></span>
|
||
|
|
For GL_TRIANGLES mode, the number of vertices should be a multiple
|
||
|
|
of three - extra vertices will be ignored. For GL_TRIANGLE_STRIP
|
||
|
|
and GL_TRIANGLE_FAN, at least three vertices should be specified.
|
||
|
|
If less than three are specified, nothing is drawn. <br>
|
||
|
|
<br>
|
||
|
|
Quadrilaterals are <span style="font-weight: bold;"></span>rendered by
|
||
|
|
the command sequence <span style="font-weight: bold;">glBegin</span>(<span
|
||
|
|
style="font-style: italic;"><span style="font-style: italic;">mode</span></span>),<span
|
||
|
|
style="font-weight: bold;">glVertex</span>, <span
|
||
|
|
style="font-weight: bold;">glVertex</span>, ... <span
|
||
|
|
style="font-weight: bold;">glEnd</span> where <span
|
||
|
|
style="font-style: italic;">mode</span> may be one of GL_QUADS or
|
||
|
|
GL_QUAD_STRIP.<span style="font-weight: bold;"></span> For
|
||
|
|
GL_QUADS, the number of vertices should be a multiple of four - extra
|
||
|
|
vertices will be ignored. For GL_QUAD_STRIP, the number of
|
||
|
|
vertices should be even and at least four. Extra vertices (one)
|
||
|
|
will be ignored.<br>
|
||
|
|
<br>
|
||
|
|
Convex polygons are <span style="font-weight: bold;"></span>rendered
|
||
|
|
by the command sequence <span style="font-weight: bold;">glBegin</span><span
|
||
|
|
style="font-style: italic;"><span style="font-style: italic;"></span></span>(GL_POLYGON),<span
|
||
|
|
style="font-weight: bold;">glVertex</span>, <span
|
||
|
|
style="font-weight: bold;">glVertex</span>, ... <span
|
||
|
|
style="font-weight: bold;">glEnd</span>.<span
|
||
|
|
style="font-style: italic;"></span><span style="font-weight: bold;"></span>
|
||
|
|
If less than three vertices are specified, nothing is drawn.<br>
|
||
|
|
<br>
|
||
|
|
<h3>4.3.1 Polygon Orientation</h3>
|
||
|
|
The <span style="font-style: italic;">winding order</span> of vertices
|
||
|
|
(clockwise or counter-clockwise) is significant. It is used to
|
||
|
|
determine the <span style="font-style: italic;">front-facing</span> or <span
|
||
|
|
style="font-style: italic;">back-facing</span> orientation of polygons.
|
||
|
|
By default, a front-facing polygon's vertices are in
|
||
|
|
counter-clockwise order (in window coordinates). Figures 2.4 and
|
||
|
|
2.5 of the OpenGL 1.2.1 specification illustrate the winding order for
|
||
|
|
front-facing triangles and quadrilaterals, respectively.<br>
|
||
|
|
<br>
|
||
|
|
The command<br>
|
||
|
|
<br>
|
||
|
|
<div style="margin-left: 40px;">void <span style="font-weight: bold;">glFrontFace</span>(GLenum<span
|
||
|
|
style="font-style: italic;"> mode</span>)<br>
|
||
|
|
</div>
|
||
|
|
<br>
|
||
|
|
specifies whether clockwise or counter-clockwise winding indicates a
|
||
|
|
front-facing polygon. If <span style="font-style: italic;">mode</span>
|
||
|
|
is GL_CW then polygons with clockwise winding are front-facing. If <span
|
||
|
|
style="font-style: italic;">mode</span> is GL_CCW then polygons with
|
||
|
|
counter-clockwise winding are front-facing. The default value is
|
||
|
|
GL_CCW. If <span style="font-style: italic;">mode</span> is not
|
||
|
|
GL_CCW or GL_CW then the error GL_INVALID_ENUM will be raised.<span
|
||
|
|
style="font-style: italic;"></span><span style="font-style: italic;"></span><br>
|
||
|
|
<br>
|
||
|
|
<h3>4.3.2 Polygon Culling</h3>
|
||
|
|
Polygons may be culled (discarded) depending on whether they are
|
||
|
|
front-facing or back-facing. The command<br>
|
||
|
|
<br>
|
||
|
|
<div style="margin-left: 40px;">void<span style="font-weight: bold;">
|
||
|
|
glCullFace</span>(GLenum <span style="font-style: italic;">mode</span>)<br>
|
||
|
|
</div>
|
||
|
|
<br>
|
||
|
|
specifies whether front-facing, back-facing or all polygons should be
|
||
|
|
culled. If <span style="font-style: italic;">mode</span> is
|
||
|
|
GL_FRONT then front-facing polygons will be culled. If <span
|
||
|
|
style="font-style: italic;">mode</span> is GL_BACK then back-facing
|
||
|
|
polygons will be culled. Otherwise, if <span style="font-style: italic;">mode</span>
|
||
|
|
is GL_FRONT_AND_BACK then all polygons will be culled. Any other
|
||
|
|
value for <span style="font-style: italic;">mode</span> will raise the
|
||
|
|
error GL_INVALID_ENUM.<br>
|
||
|
|
<br>
|
||
|
|
Polygon culling is enabled and disabled with the commands <span
|
||
|
|
style="font-weight: bold;">glEnable</span>(GL_CULL_FACE) and <span
|
||
|
|
style="font-weight: bold;">glDisable</span>(GL_CULL_FACE),
|
||
|
|
respectively.<br>
|
||
|
|
<br>
|
||
|
|
<h3>4.3.3 Polygon Antialiasing</h3>
|
||
|
|
Polygons may be antialiased in order to smooth their edges.
|
||
|
|
Polygon antialiasing is enabled and disabled with the commands <span
|
||
|
|
style="font-weight: bold;">glEnable</span>(GL_POLYGON_SMOOTH) and <span
|
||
|
|
style="font-weight: bold;">glDisable</span>(GL_POLYGON_SMOOTH).<br>
|
||
|
|
<br>
|
||
|
|
When polygon antialiasing is enabled each fragment produced by polygon,
|
||
|
|
triangle and quadrilateral rasterization will be given a <span
|
||
|
|
style="font-style: italic;">coverage</span> value which indicates how
|
||
|
|
much of the fragment is covered by the polygon. Fragments
|
||
|
|
completely inside the polygon have coverage 1.0. Fragments
|
||
|
|
completely outside the polygon have zero coverage (in theory).
|
||
|
|
Fragments which intersect the polygon's edge have a coverage value
|
||
|
|
in the range (0, 1).<br>
|
||
|
|
<br>
|
||
|
|
The fragment's alpha value is multiplied by the coverage value.
|
||
|
|
By enabling the appropriate blending mode, polygon edges will
|
||
|
|
appear smoothed.<br>
|
||
|
|
<br>
|
||
|
|
<h2>4.4 Shading</h2>
|
||
|
|
The command<br>
|
||
|
|
<br>
|
||
|
|
<div style="margin-left: 40px;"> void <span style="font-weight: bold;">glShadeModel</span>(GLenum<span
|
||
|
|
style="font-style: italic;">mode</span>)<br>
|
||
|
|
</div>
|
||
|
|
<br>
|
||
|
|
determines whether colors are interpolated between vertices during
|
||
|
|
rasterization. If <span style="font-style: italic;">mode</span> is
|
||
|
|
GL_FLAT then vertex colors are not interpolated. The color used
|
||
|
|
for drawing lines, triangles and quadrilaterals is that of the last
|
||
|
|
vertex used to specify each primitive. For polygons, the color of
|
||
|
|
the first vertex specifies the color for the entire polygon. If <span
|
||
|
|
style="font-style: italic;">mode</span> is GL_SMOOTH then vertex colors
|
||
|
|
are linearly interpolated to produce the fragment colors.<br>
|
||
|
|
<br>
|
||
|
|
<h2>4.5 Bitmap Rasterization</h2>
|
||
|
|
A bitmap is a monochromatic, binary image in which each image element
|
||
|
|
(or pixel) is represented by one bit. Fragments are only generated
|
||
|
|
for the bits (pixels) which are set. Bitmaps are commonly used to
|
||
|
|
draw text (glyphs) and markers.<br>
|
||
|
|
<br>
|
||
|
|
A bitmap is drawn with the command<br>
|
||
|
|
<br>
|
||
|
|
<div style="margin-left: 40px;">void <span style="font-weight: bold;">glBitmap</span>(GLsizei<span
|
||
|
|
style="font-style: italic;">width</span>, GLsizei <span
|
||
|
|
style="font-style: italic;">height</span>, GLfloat <span
|
||
|
|
style="font-style: italic;">xOrig</span>, GLfloat <span
|
||
|
|
style="font-style: italic;">yOrig</span>, GLfloat <span
|
||
|
|
style="font-style: italic;">xMove</span>, GLfloat <span
|
||
|
|
style="font-style: italic;">yMove</span>, const GLubyte *<span
|
||
|
|
style="font-style: italic;">image</span>)<br>
|
||
|
|
</div>
|
||
|
|
<br>
|
||
|
|
<span style="font-style: italic;">width </span>and <span
|
||
|
|
style="font-style: italic;">height</span> specify the image size in
|
||
|
|
pixels. <span style="font-style: italic;">xOrig</span> and <span
|
||
|
|
style="font-style: italic;">yOrig</span> specify the bitmap origin.
|
||
|
|
<span style="font-style: italic;">xMove</span> and <span
|
||
|
|
style="font-style: italic;">yMove</span> are added to the current
|
||
|
|
raster position after the bitmap is rasterized. <span
|
||
|
|
style="font-style: italic;">image</span> is a pointer to the bitmap
|
||
|
|
data.<br>
|
||
|
|
<br>
|
||
|
|
If the current raster position is not valid, <span
|
||
|
|
style="font-weight: bold;">glBitmap</span> has no effect.<br>
|
||
|
|
<br>
|
||
|
|
<h3>4.5.1 Bitmap Unpacking</h3>
|
||
|
|
The first step in bitmap rendering is <span style="font-style: italic;">unpacking.
|
||
|
|
</span>Unpacking is the process of extracting image data from
|
||
|
|
client memory subject to byte swapping, non-default row strides, etc.
|
||
|
|
The unpacking parameters are specified with the command<br>
|
||
|
|
<br>
|
||
|
|
<div style="margin-left: 40px;">void<span style="font-weight: bold;">
|
||
|
|
glPixelStorei</span>(GLenum pname, GLint value)<br>
|
||
|
|
</div>
|
||
|
|
<span style="font-style: italic;"></span><br>
|
||
|
|
The following unpacking parameters may be set:<br>
|
||
|
|
<br>
|
||
|
|
<table cellpadding="2" cellspacing="2" border="1"
|
||
|
|
style="text-align: left; width: 90%; margin-left: auto; margin-right: auto;">
|
||
|
|
<tbody>
|
||
|
|
<tr>
|
||
|
|
<td style="vertical-align: top;">Parameter (<span
|
||
|
|
style="font-style: italic;">pname</span>)<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">Value (<span
|
||
|
|
style="font-style: italic;">value</span>)<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">Default<br>
|
||
|
|
</td>
|
||
|
|
</tr>
|
||
|
|
<tr>
|
||
|
|
<td style="vertical-align: top;">GL_UNPACK_ROW_LENGTH<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">Width of the image in memory, in
|
||
|
|
pixels.<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">0<br>
|
||
|
|
</td>
|
||
|
|
</tr>
|
||
|
|
<tr>
|
||
|
|
<td style="vertical-align: top;">GL_UNPACK_LSB_FIRST<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">GL_FALSE indicates that the most
|
||
|
|
significant bit is unpacked first from each byte. GL_TRUE
|
||
|
|
indicates that the least significant bit is unpacked first from each
|
||
|
|
byte. <br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">GL_FALSE<br>
|
||
|
|
</td>
|
||
|
|
</tr>
|
||
|
|
</tbody>
|
||
|
|
</table>
|
||
|
|
<br>
|
||
|
|
<br>
|
||
|
|
The GL_UNPACK_ROW_LENGTH specifies the stride (in pixels) for advancing
|
||
|
|
from one row of the image to the next. If it's zero, the <span
|
||
|
|
style="font-style: italic;">width</span> parameter to <span
|
||
|
|
style="font-weight: bold;">glBitmap</span> specifies the width of the
|
||
|
|
image in memory.<br>
|
||
|
|
<br>
|
||
|
|
GL_UNPACK_LSB_FIRST determines whether the least significant or most
|
||
|
|
significant bit in each byte is unpacked first. Unpacking occurs
|
||
|
|
in left to right order (in image space).<br>
|
||
|
|
<br>
|
||
|
|
The value of bit (i, j) of the image (where i is the image row and j is
|
||
|
|
the image column) is found as follows:<br>
|
||
|
|
<br>
|
||
|
|
<div style="margin-left: 40px;">rowLength = (GL_UNPACK_ROW_LENGTH != 0)
|
||
|
|
? GL_UNPACK_ROW_LENGTH : <span style="font-style: italic;">width</span>;<br>
|
||
|
|
<br>
|
||
|
|
byte = <span style="font-style: italic;">image</span>[((rowLength + 7)
|
||
|
|
/ 8) * i + j / 8];<br>
|
||
|
|
<br>
|
||
|
|
if (GL_UNPACK_LSB_FIRST != 0)<br>
|
||
|
|
bitMask = 1 << (j % 8);<br>
|
||
|
|
else<br>
|
||
|
|
bitMask = 128 >> (j % 8);<br>
|
||
|
|
<br>
|
||
|
|
if (byte & bitMask)<br>
|
||
|
|
bit = 1;<br>
|
||
|
|
else<br>
|
||
|
|
bit = 0;<br>
|
||
|
|
<br>
|
||
|
|
</div>
|
||
|
|
<span style="font-style: italic;"><span style="font-style: italic;"></span></span>
|
||
|
|
<h3>4.5.2 Rasterization</h3>
|
||
|
|
If the current raster position is (x<sub>rp</sub>, y<sub>rp</sub>, z<sub>rp</sub>,
|
||
|
|
w<sub>rp</sub>), then the bitmap is rasterized according to the
|
||
|
|
following algorithm:<br>
|
||
|
|
<br>
|
||
|
|
for (j = 0; j < <span style="font-style: italic;">height</span>;
|
||
|
|
j++) {<br>
|
||
|
|
for (i = 0; i < <span style="font-style: italic;">width</span>;
|
||
|
|
i++) {<br>
|
||
|
|
if (bit(i,j)) {<br>
|
||
|
|
fragment.x =
|
||
|
|
floor(x<sub>rp</sub> - <span style="font-style: italic;">xOrig</span>)
|
||
|
|
+ i;<br>
|
||
|
|
fragment.y =
|
||
|
|
floor(y<sub>rp</sub> - <span style="font-style: italic;">yOrig</span>)
|
||
|
|
+ j;<br>
|
||
|
|
fragment.color
|
||
|
|
= GL_CURRENT_RASTER_COLOR;<br>
|
||
|
|
|
||
|
|
fragment.texture = GL_CURRENT_RASTER_TEXTURE_COORDS;<br>
|
||
|
|
|
||
|
|
ProcessFragment(fragment)<br>
|
||
|
|
}<br>
|
||
|
|
}<br>
|
||
|
|
}<br>
|
||
|
|
<br>
|
||
|
|
After the bitmap has been rendered the current raster position is
|
||
|
|
updated as follows:<br>
|
||
|
|
<br>
|
||
|
|
<div style="margin-left: 40px;">x<sub>rp</sub> = x<sub>rp</sub> + <span
|
||
|
|
style="font-style: italic;">xMove</span><br>
|
||
|
|
y<sub>rp</sub> = y<sub>rp</sub> + <span style="font-style: italic;">yMove</span><br>
|
||
|
|
</div>
|
||
|
|
<br>
|
||
|
|
<h3>4.5.3 Per-fragment Operations</h3>
|
||
|
|
XXX supported? See issue in appendix A.<br>
|
||
|
|
<br>
|
||
|
|
<h2>4.6 Unsupported Commands</h2>
|
||
|
|
The following commands related to rasterization are not supported by
|
||
|
|
the subset.<br>
|
||
|
|
<br>
|
||
|
|
<div style="margin-left: 40px;">Point commands:<br>
|
||
|
|
<div style="margin-left: 40px;"><span style="font-weight: bold;">glPointSize</span><br>
|
||
|
|
</div>
|
||
|
|
<br>
|
||
|
|
Polygon commands:<br>
|
||
|
|
<div style="margin-left: 40px; font-weight: bold;">glPolygonStipple<br>
|
||
|
|
glPolygonOffset<br>
|
||
|
|
glPolygonMode<br>
|
||
|
|
<br>
|
||
|
|
</div>
|
||
|
|
</div>
|
||
|
|
<div style="margin-left: 40px;">Pixel storage commands:<br>
|
||
|
|
</div>
|
||
|
|
<div style="font-weight: bold; margin-left: 80px;">glPixelStoref<br>
|
||
|
|
</div>
|
||
|
|
<br>
|
||
|
|
<br>
|
||
|
|
<h1>5. Texture Mapping<br>
|
||
|
|
</h1>
|
||
|
|
There are four elements to texture mapping: texture coordinate
|
||
|
|
specification, texture image specification, texture sampling and texture
|
||
|
|
application.<br>
|
||
|
|
<br>
|
||
|
|
Texture mapping is enabled and disabled with the commands <span
|
||
|
|
style="font-weight: bold;">glEnable</span>(GL_TEXTURE_2D) and <span
|
||
|
|
style="font-weight: bold;">glDisable</span>(GL_TEXTURE_2D).<br>
|
||
|
|
<br>
|
||
|
|
<h2>5.1 Texture Image Specification</h2>
|
||
|
|
A texture image is specified with the command:<br>
|
||
|
|
<br>
|
||
|
|
<div style="margin-left: 40px;">void <span style="font-weight: bold;">glTexImage2D</span>(GLenum<span
|
||
|
|
style="font-style: italic;"> target</span>, GLint <span
|
||
|
|
style="font-style: italic;">level</span>, GLint <span
|
||
|
|
style="font-style: italic;">internalFormat,</span> GLsizei <span
|
||
|
|
style="font-style: italic;">width,</span> GLsizei <span
|
||
|
|
style="font-style: italic;">height,</span> GLint <span
|
||
|
|
style="font-style: italic;">border,</span> GLenum <span
|
||
|
|
style="font-style: italic;">format,</span> GLenum <span
|
||
|
|
style="font-style: italic;">type,</span> const GLvoid *<span
|
||
|
|
style="font-style: italic;">pixels</span> )<br>
|
||
|
|
</div>
|
||
|
|
<br>
|
||
|
|
<span style="font-style: italic;">target</span> must be GL_TEXTURE_2D.
|
||
|
|
<span style="font-style: italic;">level </span>indicates the
|
||
|
|
mipmap level for mipmap textures. <span style="font-style: italic;">internalFormat</span>
|
||
|
|
is a hint to indicate the preferred internal storage format for the
|
||
|
|
texture. <span style="font-style: italic;">width</span> and <span
|
||
|
|
style="font-style: italic;">height </span>indicate the image size in
|
||
|
|
pixels (or texels). <span style="font-style: italic;">border </span>must
|
||
|
|
be zero. <span style="font-style: italic;">format</span> and <span
|
||
|
|
style="font-style: italic;">type</span> describe the pixel format and
|
||
|
|
data type for the incoming image. <span style="font-style: italic;">pixels</span>
|
||
|
|
points to the incoming texture image. These parameters are
|
||
|
|
described in more detail below.<br>
|
||
|
|
<br>
|
||
|
|
<h3>5.1.1 Texture Image Size and Mipmaps</h3>
|
||
|
|
<h3><span style="font-style: italic;"></span></h3>
|
||
|
|
Texture images must have dimensions (width and height) that are powers
|
||
|
|
of two. For example: 256 x 256, 32 x 1024, 1 x 8, etc. That is, it
|
||
|
|
must be the case that <span style="font-style: italic;">width </span>=
|
||
|
|
2<sup>n</sup> and <span style="font-style: italic;">height</span> = 2<sup>m</sup>
|
||
|
|
for some positive integers n and m.<br>
|
||
|
|
<br>
|
||
|
|
Mipmapping is a method of antialiasing or filtering textures to improve
|
||
|
|
their appearance. A mipmap is a set of images consisting of a base
|
||
|
|
image and a set of filtered, reduced-resolution images. If the
|
||
|
|
base image (<span style="font-style: italic;">level</span>=0) is of
|
||
|
|
width 2<sup>n</sup> and height 2<sup>m</sup> then the level 1 image must
|
||
|
|
be of width 2<sup>n-1</sup> and height 2<sup>m-1</sup>. Each mipmap
|
||
|
|
level is half the width and height of the previous level, or at least
|
||
|
|
one. The last mipmap level has a width and height of one.<br>
|
||
|
|
<br>
|
||
|
|
The following is an example of a mipmap's image levels:<br>
|
||
|
|
<br>
|
||
|
|
<table cellpadding="2" cellspacing="2" border="1"
|
||
|
|
style="text-align: left; width: 50%; margin-left: auto; margin-right: auto;">
|
||
|
|
<tbody>
|
||
|
|
<tr>
|
||
|
|
<td style="vertical-align: top;">mipmap level<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">width<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">height<br>
|
||
|
|
</td>
|
||
|
|
</tr>
|
||
|
|
<tr>
|
||
|
|
<td style="vertical-align: top;">0<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">256<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">64<br>
|
||
|
|
</td>
|
||
|
|
</tr>
|
||
|
|
<tr>
|
||
|
|
<td style="vertical-align: top;">1<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">128<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">32<br>
|
||
|
|
</td>
|
||
|
|
</tr>
|
||
|
|
<tr>
|
||
|
|
<td style="vertical-align: top;">2<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">64<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">16<br>
|
||
|
|
</td>
|
||
|
|
</tr>
|
||
|
|
<tr>
|
||
|
|
<td style="vertical-align: top;">3<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">32<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">8<br>
|
||
|
|
</td>
|
||
|
|
</tr>
|
||
|
|
<tr>
|
||
|
|
<td style="vertical-align: top;">4<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">16<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">4<br>
|
||
|
|
</td>
|
||
|
|
</tr>
|
||
|
|
<tr>
|
||
|
|
<td style="vertical-align: top;">5<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">8<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">2<br>
|
||
|
|
</td>
|
||
|
|
</tr>
|
||
|
|
<tr>
|
||
|
|
<td style="vertical-align: top;">6<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">4<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">1<br>
|
||
|
|
</td>
|
||
|
|
</tr>
|
||
|
|
<tr>
|
||
|
|
<td style="vertical-align: top;">7<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">2<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">1<br>
|
||
|
|
</td>
|
||
|
|
</tr>
|
||
|
|
<tr>
|
||
|
|
<td style="vertical-align: top;">8<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">1<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">1<br>
|
||
|
|
</td>
|
||
|
|
</tr>
|
||
|
|
</tbody>
|
||
|
|
</table>
|
||
|
|
<br>
|
||
|
|
If the <span style="font-style: italic;">width</span> or <span
|
||
|
|
style="font-style: italic;">height</span> parameters are not powers of
|
||
|
|
two, the error GL_INVALID_VALUE is raised. If the image levels in
|
||
|
|
a mipmap do not satisfy the restrictions listed above the texture is
|
||
|
|
considered to be <span style="font-style: italic;">inconsistent</span>
|
||
|
|
and the system will behave as if the texturing is disabled.<br>
|
||
|
|
<br>
|
||
|
|
<h3>5.1.2 Texture Image Formats and Unpacking</h3>
|
||
|
|
The <span style="font-weight: bold;">glTexImage2D</span> command's <span
|
||
|
|
style="font-style: italic;"><span style="font-weight: bold;"></span></span><span
|
||
|
|
style="font-style: italic;">format</span> and <span
|
||
|
|
style="font-style: italic;">type</span> parameters describe the format
|
||
|
|
of the incoming texture image. Accepted values for <span
|
||
|
|
style="font-style: italic;">format</span> are GL_INTENSITY, GL_RGB and
|
||
|
|
GL_RGBA. The <span style="font-style: italic;">type</span>
|
||
|
|
parameter must be GL_UNSIGNED_BYTE. Pixel component values are
|
||
|
|
thus in the range 0 through 255.<br>
|
||
|
|
<br>
|
||
|
|
If <span style="font-style: italic;">format</span> is GL_INTENSITY then
|
||
|
|
the image has one byte per pixel which specifies the pixel's red, green,
|
||
|
|
blue and alpha values.<span style="font-style: italic;"></span><br>
|
||
|
|
<br>
|
||
|
|
If <span style="font-style: italic;">format</span> is GL_RGB then the
|
||
|
|
image has three bytes per pixel which specify the pixel's red, green and
|
||
|
|
blue values (in that order). The alpha value defaults to 255.<br>
|
||
|
|
<br>
|
||
|
|
If <span style="font-style: italic;">format</span> is GL_RGBA then the
|
||
|
|
image has four bytes per pixel which specify the pixel's red, green,
|
||
|
|
blue and alpha values (in that order).<br>
|
||
|
|
<br>
|
||
|
|
The command<br>
|
||
|
|
<br>
|
||
|
|
<div style="margin-left: 40px;">void<span style="font-weight: bold;">
|
||
|
|
glPixelStorei</span>(GLenum <span style="font-style: italic;">pname</span>,
|
||
|
|
GLint <span style="font-style: italic;">value</span>)<br>
|
||
|
|
</div>
|
||
|
|
<br>
|
||
|
|
controls the unpacking of texture image data from client memory. <span
|
||
|
|
style="font-style: italic;">pname</span> may be GL_UNPACK_ROW_LENGTH to
|
||
|
|
indicate the stride, in pixels, between subsequent rows of the image in
|
||
|
|
client memory. If GL_UNPACK_ROW_LENGTH is zero (the default) then
|
||
|
|
the <span style="font-style: italic;">width</span> parameter to <span
|
||
|
|
style="font-weight: bold;">glTexImage2D </span>determines the stride.<span
|
||
|
|
style="font-style: italic;"></span><br>
|
||
|
|
<br>
|
||
|
|
<h3>5.1.3 Internal Texture Format</h3>
|
||
|
|
<span style="font-weight: bold;">glTexImage2D<span
|
||
|
|
style="font-style: italic;"> </span></span>converts the incoming
|
||
|
|
texture image to one of the supported internal texture formats.<br>
|
||
|
|
<br>
|
||
|
|
The <span style="font-style: italic;">internalFormat</span> parameter
|
||
|
|
indicates the desired internal format for the texture and may be either
|
||
|
|
GL_INTENSITY8, GL_RGB5 or GL_RGBA8.<br>
|
||
|
|
<br>
|
||
|
|
If <span style="font-style: italic;">internalFormat</span> is
|
||
|
|
GL_INTENSITY8 then the texture has one byte per texel (texture element)
|
||
|
|
which indicates the texel's intensity (or brightness). The
|
||
|
|
intensity is obtained from the incoming image's red channel.<br>
|
||
|
|
<br>
|
||
|
|
If <span style="font-style: italic;">internalFormat</span> is GL_RGB5
|
||
|
|
then the texture is stored with two bytes per texel: 5 bits per
|
||
|
|
red value, 5 bits per green value and 5 bits per blue value.<br>
|
||
|
|
<br>
|
||
|
|
If <span style="font-style: italic;">internalFormat </span>is
|
||
|
|
GL_RGBA8 then the texture is stored with four bytes per texel: 8
|
||
|
|
bits for each of the red, green, blue and alpha values.<br>
|
||
|
|
<br>
|
||
|
|
The internal format is also significant to texture application (see
|
||
|
|
section 5.4).<br>
|
||
|
|
<br>
|
||
|
|
<h2>5.2 Texture Coordinates</h2>
|
||
|
|
Texture coordinates control the mapping from local polygon space to
|
||
|
|
texture image space. Texture coordinates are set for each vertex
|
||
|
|
with the <span style="font-weight: bold;">glTexCoord</span> commands.
|
||
|
|
During line and polygon rasterization the vertex's texture
|
||
|
|
coordinates are interpolated across the primitive to produce a texture
|
||
|
|
coordinate for each fragment. The fragment texture coordinates are
|
||
|
|
used to sample the current texture image.<br>
|
||
|
|
<br>
|
||
|
|
Texture coordinates are normally in the range [0, 1]. Values
|
||
|
|
outside that range are processed according to the <span
|
||
|
|
style="font-style: italic;">texture wrap mode</span>. The
|
||
|
|
texture wrap mode is set with the command<br>
|
||
|
|
<br>
|
||
|
|
<div style="margin-left: 40px;">void <span style="font-weight: bold;">glTexParameteri</span>(GLenum<span
|
||
|
|
style="font-style: italic;"> target</span>, GLenum <span
|
||
|
|
style="font-style: italic;">pname</span>, GLint <span
|
||
|
|
style="font-style: italic;">value</span>)<br>
|
||
|
|
<br>
|
||
|
|
</div>
|
||
|
|
<span style="font-style: italic;">target</span> must be GL_TEXTURE_2D.
|
||
|
|
If <span style="font-style: italic;">pname</span> is
|
||
|
|
GL_TEXTURE_WRAP_S or GL_TEXTURE_WRAP_T then <span
|
||
|
|
style="font-style: italic;">value</span> must be either
|
||
|
|
GL_CLAMP_TO_EDGE or GL_REPEAT.<br>
|
||
|
|
<br>
|
||
|
|
For GL_CLAMP_TO_EDGE, texture coordinates are effectively clamped to
|
||
|
|
the interval [0, 1].<br>
|
||
|
|
<br>
|
||
|
|
For GL_REPEAT, the integer part of texture coordinates is ignored; only
|
||
|
|
the fractional part of the texture coordinates is used. This
|
||
|
|
allows texture images to repeated or tiled across an object.<br>
|
||
|
|
<br>
|
||
|
|
<h2>5.3 Texture Sampling</h2>
|
||
|
|
Texture sampling is the process of using texture coordinates to extract
|
||
|
|
a color from the texture image. Multiple, weighted samples may be
|
||
|
|
taken from the texture and combined during the filtering step.<br>
|
||
|
|
<br>
|
||
|
|
During texture coordinate interpolation a <span
|
||
|
|
style="font-style: italic;">level of detail</span> value (lambda) is
|
||
|
|
computed for each fragment. For a mipmapped texture, lambda
|
||
|
|
determines which level (or levels) of the mipmap will be sampled to
|
||
|
|
obtain the texture color.<br>
|
||
|
|
<br>
|
||
|
|
If lambda indicates that multiple texels map to a single screen pixel,
|
||
|
|
then the texture <span style="font-style: italic;">minification</span>
|
||
|
|
filter will be used. Otherwise, if lambda indicates that a single
|
||
|
|
texel maps to multiple screen pixels, then the texture <span
|
||
|
|
style="font-style: italic;">magnification</span> filter will be used.<br>
|
||
|
|
<span style="font-weight: bold;"></span><span
|
||
|
|
style="font-style: italic;"></span><br>
|
||
|
|
<h3>5.3.1 Texture Minification</h3>
|
||
|
|
The texture minification filter is set with the <span
|
||
|
|
style="font-weight: bold;">glTexParameteri </span><span
|
||
|
|
style="font-style: italic;"></span><span style="font-weight: bold;"></span><span
|
||
|
|
style="font-style: italic;"></span> command by setting <span
|
||
|
|
style="font-style: italic;">target</span> to GL_TEXTURE_2D, setting <span
|
||
|
|
style="font-style: italic;">pname</span> to GL_TEXTURE_MIN_FILTER and
|
||
|
|
setting <span style="font-style: italic;">value</span> to GL_NEAREST,
|
||
|
|
GL_LINEAR, GL_NEAREST_MIPMAP_NEAREST,
|
||
|
|
GL_NEAREST_MIPMAP_LINEAR, GL_LINEAR_MIPMAP_NEAREST or
|
||
|
|
GL_LINEAR_MIPMAP_LINEAR.<br>
|
||
|
|
<br>
|
||
|
|
GL_NEAREST samples the texel nearest the texture coordinate in the
|
||
|
|
level 0 texture image.<br>
|
||
|
|
<br>
|
||
|
|
GL_LINEAR samples the four texels around the texture coordinate in the
|
||
|
|
level 0 texture image. The four texels are linearly weighted to
|
||
|
|
compute the final texel value.<br>
|
||
|
|
<br>
|
||
|
|
GL_NEAREST_MIPMAP_NEAREST samples the texel nearest the texture
|
||
|
|
coordinate in the level N texture image. N is the level of detail
|
||
|
|
and is computed by the partial derivatives of the texture coordinates
|
||
|
|
with respect to the window coordinates.<br>
|
||
|
|
<br>
|
||
|
|
GL_NEAREST_MIPMAP_LINEAR samples two texels nearest the texture
|
||
|
|
coordinates in the level N and N+1 texture images. The two texels
|
||
|
|
are linearly weighted to compute the final texel value. N is the
|
||
|
|
level of detail and is computed by the partial derivatives of the
|
||
|
|
texture coordinates with respect to the window coordinates.<br>
|
||
|
|
<br>
|
||
|
|
GL_LINEAR_MIPMAP_NEAREST samples four texels around the texture
|
||
|
|
coordinate in the level N texture image. The four texels are
|
||
|
|
linearly weighted to compute the final texel value. N is the level
|
||
|
|
of detail and is computed by the partial derivatives of the texture
|
||
|
|
coordinates with respect to the window coordinates.<br>
|
||
|
|
<br>
|
||
|
|
GL_LINEAR_MIPMAP_LINEAR samples four texels around the texture
|
||
|
|
coordinate in the level N texture image and four texels around the
|
||
|
|
texture coordinate in the level N+1 texture image. The eight
|
||
|
|
texels are linearly weighted to compute the final texel value. N
|
||
|
|
is the level of detail and is computed by the partial derivatives of the
|
||
|
|
texture coordinates with respect to the window coordinates.<br>
|
||
|
|
<br>
|
||
|
|
Filter modes other than GL_LINEAR and GL_NEAREST requires that the
|
||
|
|
texture have a complete set of mipmaps. If the mipmap is
|
||
|
|
incomplete, it is as if texturing is disabled.<br>
|
||
|
|
<br>
|
||
|
|
<h3>5.3.2 Texture Magnification</h3>
|
||
|
|
The texture magnification filter is set with the <span
|
||
|
|
style="font-weight: bold;">glTexParameteri </span><span
|
||
|
|
style="font-style: italic;"></span><span style="font-weight: bold;"></span>command
|
||
|
|
by setting <span style="font-style: italic;">target</span> to
|
||
|
|
GL_TEXTURE_2D, setting <span style="font-style: italic;">pname</span> to
|
||
|
|
GL_TEXTURE_MAG_FILTER and setting <span style="font-style: italic;">value</span>
|
||
|
|
to GL_NEAREST or GL_LINEAR.<br>
|
||
|
|
<br>
|
||
|
|
GL_NEAREST samples the texel nearest the texture coordinate in the
|
||
|
|
level 0 texture image.<br>
|
||
|
|
<br>
|
||
|
|
GL_LINEAR samples the four texels around the texture coordinate in the
|
||
|
|
level 0 texture image. The four texels are linearly weighted to
|
||
|
|
compute the final texel value.<br>
|
||
|
|
<br>
|
||
|
|
<h2>5.4 Texture Application</h2>
|
||
|
|
The sampled texture value is combined with the incoming fragment color
|
||
|
|
to produce a new fragment color. The fragment and texture colors
|
||
|
|
are combined according to the texture environment mode and the current
|
||
|
|
texture's base internal format. The texture environment mode is
|
||
|
|
set with the command<br>
|
||
|
|
<br>
|
||
|
|
<div style="margin-left: 40px;">void<span style="font-weight: bold;">
|
||
|
|
glTexEnvi</span>(GLenum <span style="font-style: italic;">target</span>,
|
||
|
|
GLenum <span style="font-style: italic;">pname</span>, GLint <span
|
||
|
|
style="font-style: italic;">value</span>)<br>
|
||
|
|
</div>
|
||
|
|
<br>
|
||
|
|
<span style="font-style: italic;">target</span> must be GL_TEXTURE_ENV.
|
||
|
|
If <span style="font-style: italic;">pname</span> is
|
||
|
|
GL_TEXTURE_ENV_MODE then <span style="font-style: italic;">value</span>
|
||
|
|
must be one of GL_REPLACE, GL_MODULATE, GL_DECAL, or GL_BLEND.<br>
|
||
|
|
<br>
|
||
|
|
There is also a <span style="font-style: italic;">texture environment
|
||
|
|
color</span> that can factor into texture application. The texture
|
||
|
|
environment color can be set with the command<br>
|
||
|
|
<br>
|
||
|
|
<div style="margin-left: 40px;">void<span style="font-weight: bold;">
|
||
|
|
glTexEnvfv</span>(GLenum <span style="font-style: italic;">target</span>,
|
||
|
|
GLenum <span style="font-style: italic;">pname</span>, const GLfloat *<span
|
||
|
|
style="font-style: italic;">value</span>)<br>
|
||
|
|
</div>
|
||
|
|
<span style="font-style: italic;"></span><br>
|
||
|
|
<span style="font-style: italic;">target</span> must be GL_TEXTURE_ENV.
|
||
|
|
If <span style="font-style: italic;">pname</span> is
|
||
|
|
GL_TEXTURE_ENV_COLOR then <span style="font-style: italic;">value </span>must
|
||
|
|
point to an array of four values which specify the red, green, blue,
|
||
|
|
and alpha values of the texture environment color. The values are
|
||
|
|
clamped to the range [0, 1]. The default color is (0, 0, 0, 0).<br>
|
||
|
|
<span style="font-style: italic;"></span><br>
|
||
|
|
The following table describes the arithmetic used for each combination
|
||
|
|
of environment mode and base internal format. (Rf, Gf, Bf, Af) is
|
||
|
|
the incoming fragment color. (Rt, Gt, Bt, At) is the sampled
|
||
|
|
texture color. Lt is the sampled texture luminance. <span
|
||
|
|
style="font-style: italic;"></span>'It' is the sampled texture
|
||
|
|
intensity. (Rc, Gc, Bc, Ac) is the texture environment color.
|
||
|
|
(Rv, Gv, Bv, Av) is the resulting value.<br>
|
||
|
|
<br>
|
||
|
|
<br>
|
||
|
|
<table cellpadding="2" cellspacing="2" border="1"
|
||
|
|
style="text-align: left; width: 90%; margin-left: auto; margin-right: auto;">
|
||
|
|
<tbody>
|
||
|
|
<tr>
|
||
|
|
<td style="vertical-align: top;">Base Internal Format<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">GL_REPLACE<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">GL_MODULATE<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">GL_DECAL<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">GL_BLEND<br>
|
||
|
|
</td>
|
||
|
|
</tr>
|
||
|
|
<tr>
|
||
|
|
<td style="vertical-align: top;">GL_INTENSITY<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">Rv = It<br>
|
||
|
|
Gv = It<br>
|
||
|
|
Bv = It<br>
|
||
|
|
Bf = It<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">Rv = Rf * It<br>
|
||
|
|
Gv = Gf * It<br>
|
||
|
|
Bv = Bf * It<br>
|
||
|
|
Av = Af * It</td>
|
||
|
|
<td style="vertical-align: top;">undefined<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">Rv = Rf*(1-It) + Rc*It<br>
|
||
|
|
Gv = Gf*(1-It) + Gc*It<br>
|
||
|
|
Bv = Bf*(1-It) + Bc*It<br>
|
||
|
|
Av = Af*(1-It) + Ac*It</td>
|
||
|
|
</tr>
|
||
|
|
<tr>
|
||
|
|
<td style="vertical-align: top;">GL_RGB<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">Rv = Rt<br>
|
||
|
|
Gv = Gt<br>
|
||
|
|
Bv = Bt<br>
|
||
|
|
Av = Af<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">Rv = Rf * Rt<br>
|
||
|
|
Gv = Gf * Gt<br>
|
||
|
|
Bv = Bf * Bt<br>
|
||
|
|
Av = Af<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">Rv = Rt<br>
|
||
|
|
Gv = Gt<br>
|
||
|
|
Bv = Bt<br>
|
||
|
|
Av = Af</td>
|
||
|
|
<td style="vertical-align: top;">Rv = Rf*(1-Rt) + Rc*Rt<br>
|
||
|
|
Gv = Gf*(1-Gt) + Gc*Gt<br>
|
||
|
|
Bv = Bf*(1-Bt) + Bc*Bt<br>
|
||
|
|
Av = Af</td>
|
||
|
|
</tr>
|
||
|
|
<tr>
|
||
|
|
<td style="vertical-align: top;">GL_RGBA<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">Rv = Rt<br>
|
||
|
|
Gv = Gt<br>
|
||
|
|
Bv = Bt<br>
|
||
|
|
Av = At<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">Rv = Rf * Rt<br>
|
||
|
|
Gv = Gf * Gt<br>
|
||
|
|
Bv = Bf * Bt<br>
|
||
|
|
Av = Af * At</td>
|
||
|
|
<td style="vertical-align: top;">Rv = Rf*(1-At) + Rt*At<br>
|
||
|
|
Gv = Gf*(1-At) + Gt*At<br>
|
||
|
|
Bv = Bf*(1-At) + Bt*At<br>
|
||
|
|
Av = Af<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">Rv = Rf*(1-Rt) + Rc*Rt<br>
|
||
|
|
Gv = Gf*(1-Gt) + Gc*Gt<br>
|
||
|
|
Bv = Bf*(1-Bt) + Bc*Bt<br>
|
||
|
|
Av = Af*At</td>
|
||
|
|
</tr>
|
||
|
|
</tbody>
|
||
|
|
</table>
|
||
|
|
<br>
|
||
|
|
<br>
|
||
|
|
<br>
|
||
|
|
<h2>5.5 Texture Objects</h2>
|
||
|
|
Texture objects encapsulate a set of texture images (mipmap) and
|
||
|
|
related state into a named object. This facilitates use of
|
||
|
|
multiple textures in an application. Texture objects are named
|
||
|
|
with GLuints (unsigned integers). There is a default texture
|
||
|
|
object with the name/identifier zero which can never be deleted.<br>
|
||
|
|
<br>
|
||
|
|
<h3>5.5.1 Creating Texture Objects</h3>
|
||
|
|
A texture object is created by binding a new GLuint identifier to the
|
||
|
|
GL_TEXTURE_2D target with the command:<br>
|
||
|
|
<br>
|
||
|
|
<div style="margin-left: 40px;">void <span style="font-weight: bold;">glBindTexture</span>(GLenum<span
|
||
|
|
style="font-style: italic;"> target</span>, GLuint <span
|
||
|
|
style="font-style: italic;">textureID</span>)<br>
|
||
|
|
</div>
|
||
|
|
<br>
|
||
|
|
<span style="font-style: italic;">target</span> must be GL_TEXTURE_2D.
|
||
|
|
<span style="font-style: italic;">textureID</span> may be any
|
||
|
|
unsigned integer. If <span style="font-style: italic;">textureID</span>
|
||
|
|
does not name an existing texture object, a new texture object with that
|
||
|
|
ID will be created, initialized to the default state. Whether the
|
||
|
|
ID is new or existed previously, that named texture object is bound as
|
||
|
|
the <span style="font-style: italic;">current texture object</span>.
|
||
|
|
Subsequent <span style="font-weight: bold;">glTexParameter </span>and<span
|
||
|
|
style="font-weight: bold;">glTexImage2D<span
|
||
|
|
style="font-style: italic;"> </span></span>calls will effect the
|
||
|
|
current texture object.<br>
|
||
|
|
<span style="font-style: italic;"></span><span
|
||
|
|
style="font-weight: bold;"><span style="font-style: italic;"> </span></span><br>
|
||
|
|
<h3>5.5.2 Deleting Texture Objects</h3>
|
||
|
|
One or more texture objects may be deleted with the command:<br>
|
||
|
|
<br>
|
||
|
|
<div style="margin-left: 40px;">void <span style="font-weight: bold;">glDeleteTextures</span>(GLsizei<span
|
||
|
|
style="font-style: italic;">n</span>, const GLuint *<span
|
||
|
|
style="font-style: italic;">textureIDs</span>)<br>
|
||
|
|
</div>
|
||
|
|
<br>
|
||
|
|
<span style="font-style: italic;">textureIDs</span> is an array of <span
|
||
|
|
style="font-style: italic;">n</span> texture IDs. The named
|
||
|
|
texture objects will be deleted. If the current texture object is
|
||
|
|
deleted the default texture object (number 0) will be bound as the
|
||
|
|
current texture object.<br>
|
||
|
|
<br>
|
||
|
|
<h3>5.5.3 Allocating Texture Object Identifiers</h3>
|
||
|
|
A list of new, unused texture IDs can be obtained by calling the command<br>
|
||
|
|
<br>
|
||
|
|
<div style="margin-left: 40px;">void <span style="font-weight: bold;">glGenTextures</span>(GLsizei<span
|
||
|
|
style="font-style: italic;"> n</span>, GLuint *<span
|
||
|
|
style="font-style: italic;">textureIDs</span>)<br>
|
||
|
|
</div>
|
||
|
|
<br>
|
||
|
|
An array of <span style="font-style: italic;">n</span> unused texture
|
||
|
|
IDs will be returned in the <span style="font-style: italic;">textureIDs</span>
|
||
|
|
array.<br>
|
||
|
|
<br>
|
||
|
|
<br>
|
||
|
|
<h1>6. Per-fragment Operations</h1>
|
||
|
|
The fragments produced by rasterization are subjected to a number of
|
||
|
|
operations which either modify the fragment or test the fragment
|
||
|
|
(discarding the fragment if the test fails.) This chapter
|
||
|
|
describes the per-fragment operations. They are presented in the
|
||
|
|
order in which they're performed. If a fragment fails a test it is
|
||
|
|
discarded and not subjected to subsequent tests or modifications.<br>
|
||
|
|
<br>
|
||
|
|
<h2>6.1 Scissor Test</h2>
|
||
|
|
The scissor test limits rendering to a 2-D rectangular region of the
|
||
|
|
framebuffer. The command<br>
|
||
|
|
<br>
|
||
|
|
<div style="margin-left: 40px;">void <span style="font-weight: bold;">glScissor</span>(GLint<span
|
||
|
|
style="font-style: italic;">x</span>, GLint <span
|
||
|
|
style="font-style: italic;">y</span>, GLsizei <span
|
||
|
|
style="font-style: italic;">width</span>, GLsizei<span
|
||
|
|
style="font-style: italic;"> height</span>)<br>
|
||
|
|
</div>
|
||
|
|
<br>
|
||
|
|
defines a clipping region with the lower-left corner at (<span
|
||
|
|
style="font-style: italic;">x, y</span>) and the given <span
|
||
|
|
style="font-style: italic;">width</span> and <span
|
||
|
|
style="font-style: italic;">height</span>. The scissor test is
|
||
|
|
enabled and disabled with the command <span style="font-weight: bold;">glEnable</span>(GL_SCISSOR_TEST)
|
||
|
|
and <span style="font-weight: bold;">glDisable</span>(GL_SCISSOR_TEST).<br>
|
||
|
|
<br>
|
||
|
|
If the incoming fragment's position is (x<sub>f</sub>, y<sub>f</sub>)
|
||
|
|
then the fragment will pass the test if <span
|
||
|
|
style="font-style: italic;">x</span> <= x<sub>f</sub> < <span
|
||
|
|
style="font-style: italic;">x</span> + <span
|
||
|
|
style="font-style: italic;">width</span> and <span
|
||
|
|
style="font-style: italic;">y</span> <= y<sub>f</sub> < <span
|
||
|
|
style="font-style: italic;">y</span> + <span
|
||
|
|
style="font-style: italic;">height. </span>Otherwise, the
|
||
|
|
fragment is discarded.<br>
|
||
|
|
<br>
|
||
|
|
If <span style="font-style: italic;">width</span> or <span
|
||
|
|
style="font-style: italic;">height</span> is less than zero the error
|
||
|
|
GL_INVALID_VALUE is raised. The default scissor rectangle bounds
|
||
|
|
are (0, 0, w, h) where w is the initial window width and h is the
|
||
|
|
initial window height. The scissor test is disabled by default.<br>
|
||
|
|
<br>
|
||
|
|
<h2>6.2 Alpha Test</h2>
|
||
|
|
The alpha test compares the fragment's alpha value against a reference
|
||
|
|
value and discards the fragment if the comparison fails. The test
|
||
|
|
is specified by the command<br>
|
||
|
|
<br>
|
||
|
|
<div style="margin-left: 40px;">void <span style="font-weight: bold;">glAlphaFunc</span>(GLenum<span
|
||
|
|
style="font-style: italic;">mode</span>, GLclampf <span
|
||
|
|
style="font-style: italic;">reference</span>)<br>
|
||
|
|
</div>
|
||
|
|
<br>
|
||
|
|
<span style="font-style: italic;">mode</span> specifies an inequality
|
||
|
|
and <span style="font-style: italic;">reference</span> specifies a value
|
||
|
|
to compare against. The following table lists all possible
|
||
|
|
modes <span style="font-style: italic;"></span>and the
|
||
|
|
corresponding test:<br>
|
||
|
|
<br>
|
||
|
|
<table cellpadding="2" cellspacing="2" border="1"
|
||
|
|
style="text-align: left; width: 50%; margin-left: auto; margin-right: auto;">
|
||
|
|
<tbody>
|
||
|
|
<tr>
|
||
|
|
<td style="vertical-align: top;">Comparison mode<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">The test passes if<br>
|
||
|
|
</td>
|
||
|
|
</tr>
|
||
|
|
<tr>
|
||
|
|
<td style="vertical-align: top;">GL_LESS<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">alpha < <span
|
||
|
|
style="font-style: italic;">reference</span><br>
|
||
|
|
</td>
|
||
|
|
</tr>
|
||
|
|
<tr>
|
||
|
|
<td style="vertical-align: top;">GL_LEQUAL<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">alpha <= <span
|
||
|
|
style="font-style: italic;">reference</span></td>
|
||
|
|
</tr>
|
||
|
|
<tr>
|
||
|
|
<td style="vertical-align: top;">GL_GREATER<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">alpha > <span
|
||
|
|
style="font-style: italic;">reference</span></td>
|
||
|
|
</tr>
|
||
|
|
<tr>
|
||
|
|
<td style="vertical-align: top;">GL_GEQUAL<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">alpha >= <span
|
||
|
|
style="font-style: italic;">reference</span></td>
|
||
|
|
</tr>
|
||
|
|
<tr>
|
||
|
|
<td style="vertical-align: top;">GL_EQUAL<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">alpha == <span
|
||
|
|
style="font-style: italic;">reference</span></td>
|
||
|
|
</tr>
|
||
|
|
<tr>
|
||
|
|
<td style="vertical-align: top;">GL_NOTEQUAL<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">alpha != <span
|
||
|
|
style="font-style: italic;">reference</span></td>
|
||
|
|
</tr>
|
||
|
|
<tr>
|
||
|
|
<td style="vertical-align: top;">GL_NEVER<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">never pass<br>
|
||
|
|
</td>
|
||
|
|
</tr>
|
||
|
|
<tr>
|
||
|
|
<td style="vertical-align: top;">GL_ALWAYS<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">always passes<br>
|
||
|
|
</td>
|
||
|
|
</tr>
|
||
|
|
</tbody>
|
||
|
|
</table>
|
||
|
|
<br>
|
||
|
|
The <span style="font-style: italic;">reference</span> parameter is
|
||
|
|
clamped to the range [0, 1].<br>
|
||
|
|
<br>
|
||
|
|
The alpha test is enabled and disabled with the commands <span
|
||
|
|
style="font-weight: bold;">glEnable</span>(GL_ALPHA_TEST) and <span
|
||
|
|
style="font-weight: bold;">glDisable</span>(GL_ALPHA_TEST).<br>
|
||
|
|
<br>
|
||
|
|
The default mode is GL_ALWAYS and the default reference value is 0.<br>
|
||
|
|
<br>
|
||
|
|
<h2>6.3 Stencil Test</h2>
|
||
|
|
The stencil buffer stores an N-bit integer value for each pixel in the
|
||
|
|
frame buffer. The stencil test compares the stencil buffer value
|
||
|
|
at the fragment's position to a reference value and possibly discards
|
||
|
|
the fragment based on the outcome. Furthermore, the stencil buffer
|
||
|
|
value may be updated or modified depending on the outcome. If
|
||
|
|
there is no stencil buffer the stencil test is bypassed.<br>
|
||
|
|
<br>
|
||
|
|
Stenciling is controlled by the commands<br>
|
||
|
|
<br>
|
||
|
|
<div style="margin-left: 40px;">void <span style="font-weight: bold;">glStencilFunc</span>(GLenum<span
|
||
|
|
style="font-style: italic;">func</span>, GLint <span
|
||
|
|
style="font-style: italic;">ref</span>, GLuint <span
|
||
|
|
style="font-style: italic;">mask</span>)<br>
|
||
|
|
void <span style="font-weight: bold;">glStencilOp</span>(GLenum <span
|
||
|
|
style="font-style: italic;">stencilFail</span>, GLenum <span
|
||
|
|
style="font-style: italic;">depthTestFail</span>, GLenum <span
|
||
|
|
style="font-style: italic;">depthTestPass</span>)<br>
|
||
|
|
</div>
|
||
|
|
<br>
|
||
|
|
The <span style="font-weight: bold;">glStencilFunc<span
|
||
|
|
style="font-style: italic;"> </span></span>command controls the
|
||
|
|
stencil test while <span style="font-weight: bold;">glStencilOp</span>
|
||
|
|
command controls the how the stencil buffer is updated/modified after
|
||
|
|
the test.<br>
|
||
|
|
<br>
|
||
|
|
<span style="font-style: italic;">ref</span> is clamped to the range [0,
|
||
|
|
2<sup>N</sup>-1] where N is the number of bits per stencil value in the
|
||
|
|
stencil buffer.<span style="font-style: italic;"></span><br>
|
||
|
|
<br>
|
||
|
|
The following table lists all possible values for the <span
|
||
|
|
style="font-style: italic;">func</span> parameter and when the stencil
|
||
|
|
test will pass. Both the stencil buffer value and the stencil
|
||
|
|
reference value are bit-wise ANDed with the <span
|
||
|
|
style="font-style: italic;">mask</span> parameter before the test.<br>
|
||
|
|
<br>
|
||
|
|
<span style="font-style: italic;"></span><span
|
||
|
|
style="font-style: italic;"></span><span style="font-style: italic;"></span>
|
||
|
|
<table
|
||
|
|
style="text-align: left; margin-left: auto; margin-right: auto; width: 70%;"
|
||
|
|
border="1" cellspacing="2" cellpadding="2">
|
||
|
|
<tbody>
|
||
|
|
<tr>
|
||
|
|
<td style="vertical-align: top;">Stencil <span
|
||
|
|
style="font-style: italic;">func</span> value<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">Stencil test passes if<br>
|
||
|
|
</td>
|
||
|
|
</tr>
|
||
|
|
<tr>
|
||
|
|
<td style="vertical-align: top;">GL_LESS<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;"><span style="font-style: italic;">(ref</span>&<span
|
||
|
|
style="font-style: italic;">mask)</span> < (stencil buffer value
|
||
|
|
& <span style="font-style: italic;">mask)</span><br>
|
||
|
|
</td>
|
||
|
|
</tr>
|
||
|
|
<tr>
|
||
|
|
<td style="vertical-align: top;">GL_LEQUAL<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;"><span style="font-style: italic;">(ref</span>
|
||
|
|
& <span style="font-style: italic;">mask) </span><= (stencil
|
||
|
|
buffer value & <span style="font-style: italic;">mask)</span></td>
|
||
|
|
</tr>
|
||
|
|
<tr>
|
||
|
|
<td style="vertical-align: top;">GL_GREATER<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;"><span style="font-style: italic;">(ref</span>
|
||
|
|
& <span style="font-style: italic;">mask) </span>> (stencil
|
||
|
|
buffer value & <span style="font-style: italic;">mask)</span></td>
|
||
|
|
</tr>
|
||
|
|
<tr>
|
||
|
|
<td style="vertical-align: top;">GL_GEQUAL<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;"><span style="font-style: italic;">(ref</span>
|
||
|
|
& <span style="font-style: italic;">mask) </span>>= (stencil
|
||
|
|
buffer value & <span style="font-style: italic;">mask)</span></td>
|
||
|
|
</tr>
|
||
|
|
<tr>
|
||
|
|
<td style="vertical-align: top;">GL_EQUAL<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;"><span style="font-style: italic;">(ref</span>
|
||
|
|
& <span style="font-style: italic;">mask) </span>== (stencil
|
||
|
|
buffer value & <span style="font-style: italic;">mask)</span></td>
|
||
|
|
</tr>
|
||
|
|
<tr>
|
||
|
|
<td style="vertical-align: top;">GL_NOTEQUAL<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;"><span style="font-style: italic;">(ref</span>
|
||
|
|
& <span style="font-style: italic;">mask) </span>!= (stencil
|
||
|
|
buffer value & <span style="font-style: italic;">mask)</span></td>
|
||
|
|
</tr>
|
||
|
|
<tr>
|
||
|
|
<td style="vertical-align: top;">GL_NEVER<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">never passes<br>
|
||
|
|
</td>
|
||
|
|
</tr>
|
||
|
|
<tr>
|
||
|
|
<td style="vertical-align: top;">GL_ALWAYS<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">always passes<br>
|
||
|
|
</td>
|
||
|
|
</tr>
|
||
|
|
</tbody>
|
||
|
|
</table>
|
||
|
|
<br>
|
||
|
|
<span style="font-style: italic;"></span><br>
|
||
|
|
If the stencil test passes, the fragment is passed to the next
|
||
|
|
per-fragment operation. Otherwise, if the stencil test fails, the
|
||
|
|
value in the stencil buffer is updated according to the value of the <span
|
||
|
|
style="font-style: italic;">stencilFail</span> parameter to <span
|
||
|
|
style="font-weight: bold;">glStencilOp</span>.<br>
|
||
|
|
<br>
|
||
|
|
<table cellpadding="2" cellspacing="2" border="1"
|
||
|
|
style="text-align: left; width: 70%; margin-left: auto; margin-right: auto;">
|
||
|
|
<tbody>
|
||
|
|
<tr>
|
||
|
|
<td style="vertical-align: top;"><span style="font-style: italic;">stencilFail</span>
|
||
|
|
value<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">New stencil buffer value<br>
|
||
|
|
</td>
|
||
|
|
</tr>
|
||
|
|
<tr>
|
||
|
|
<td style="vertical-align: top;">GL_KEEP<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">originalValue<br>
|
||
|
|
</td>
|
||
|
|
</tr>
|
||
|
|
<tr>
|
||
|
|
<td style="vertical-align: top;">GL_ZERO<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">0<br>
|
||
|
|
</td>
|
||
|
|
</tr>
|
||
|
|
<tr>
|
||
|
|
<td style="vertical-align: top;">GL_INVERT<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">BitWiseInvert(originalValue)
|
||
|
|
i.e. ~originalValue<br>
|
||
|
|
</td>
|
||
|
|
</tr>
|
||
|
|
<tr>
|
||
|
|
<td style="vertical-align: top;">GL_REPLACE<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;"><span style="font-style: italic;">ref</span><br>
|
||
|
|
</td>
|
||
|
|
</tr>
|
||
|
|
<tr>
|
||
|
|
<td style="vertical-align: top;">GL_INCR<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">originalValue + 1, clamped to
|
||
|
|
[0, 2<sup>N</sup>-1]</td>
|
||
|
|
</tr>
|
||
|
|
<tr>
|
||
|
|
<td style="vertical-align: top;">GL_DECR<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">originalValue - 1, clamped to
|
||
|
|
[0, 2<sup>N</sup>-1]</td>
|
||
|
|
</tr>
|
||
|
|
</tbody>
|
||
|
|
</table>
|
||
|
|
<span style="font-style: italic;"></span><span
|
||
|
|
style="font-style: italic;"></span><br>
|
||
|
|
<br>
|
||
|
|
The <span style="font-style: italic;">depthTestFail</span> and <span
|
||
|
|
style="font-style: italic;">depthTestPass</span> parameters to <span
|
||
|
|
style="font-weight: bold;">glStencilOp</span> are ignored. Values
|
||
|
|
for <span style="font-style: italic;">func</span> and <span
|
||
|
|
style="font-style: italic;">stencilFail</span> other than those listed
|
||
|
|
in the table will cause the error GL_INVALID_ENUM to be raised.<br>
|
||
|
|
<br>
|
||
|
|
The stencil test is enabled and disabled with the commands <span
|
||
|
|
style="font-weight: bold;">glEnable</span>(GL_STENCIL_TEST) and <span
|
||
|
|
style="font-weight: bold;">glDisable</span>(GL_STENCIL_TEST).<br>
|
||
|
|
<br>
|
||
|
|
The default stencil function is GL_ALWAYS. The default stencil
|
||
|
|
reference value is 0. The default stencil mask is ~0. The
|
||
|
|
default stencil fail operation is GL_KEEP.<br>
|
||
|
|
<br>
|
||
|
|
Values written into the stencil buffer are masked with the command<br>
|
||
|
|
<br>
|
||
|
|
<div style="margin-left: 40px;">void <span style="font-weight: bold;">glStencilMask</span>(GLuint<span
|
||
|
|
style="font-style: italic;">mask</span>)<br>
|
||
|
|
</div>
|
||
|
|
<br>
|
||
|
|
Only the bits which are set in <span style="font-style: italic;">mask</span>
|
||
|
|
will be modified in the stencil buffer when written to. If each
|
||
|
|
stencil buffer value has N bits, only the least significant N bits of <span
|
||
|
|
style="font-style: italic;">mask</span> are relevant. The default
|
||
|
|
stencil mask is ~0.<br>
|
||
|
|
<br>
|
||
|
|
<h2>6.4 Blending and Logicop</h2>
|
||
|
|
Blending or a logic operation combines the incoming fragment color with
|
||
|
|
the destination frame buffer color according to a blending equation or
|
||
|
|
bit-wise Boolean logical operation.<br>
|
||
|
|
<br>
|
||
|
|
Blending is enabled and disabled with the commands <span
|
||
|
|
style="font-weight: bold;">glEnable</span>(GL_BLEND) and <span
|
||
|
|
style="font-weight: bold;">glDisable</span>(GL_BLEND).<br>
|
||
|
|
<br>
|
||
|
|
The logic operation is enabled and disabled with the commands <span
|
||
|
|
style="font-weight: bold;">glEnable</span>(GL_LOGIC_OP) and <span
|
||
|
|
style="font-weight: bold;">glDisable</span>(GL_LOGIC_OP).<br>
|
||
|
|
<br>
|
||
|
|
If both blending and the logic operation are enabled, the logic
|
||
|
|
operation has higher priority; blending is bypassed.<br>
|
||
|
|
<br>
|
||
|
|
<h3>6.4.1 Logic Op</h3>
|
||
|
|
The command<br>
|
||
|
|
<br>
|
||
|
|
<div style="margin-left: 40px;">void <span style="font-weight: bold;">glLogicop</span>(GLenum<span
|
||
|
|
style="font-style: italic;">mode</span>)<br>
|
||
|
|
<br>
|
||
|
|
</div>
|
||
|
|
Specifies the Boolean logic operation for combining the incoming
|
||
|
|
fragment color with the destination frame buffer color. Both the
|
||
|
|
incoming fragment color and destination frame buffer colors are
|
||
|
|
interpreted as four-tuples of unsigned integer color components in the
|
||
|
|
range [0, 2<sup>N</sup>-1] where N is the number of bits per color
|
||
|
|
channel. N may not be the same for all color channels.<br>
|
||
|
|
<br>
|
||
|
|
The following table lists all values for <span
|
||
|
|
style="font-style: italic;">mode</span> and the boolean arithmetic used
|
||
|
|
to combine the incoming fragment color value (src)<span
|
||
|
|
style="font-style: italic;"></span><span style="font-style: italic;"></span><span
|
||
|
|
style="font-style: italic;"></span><span style="font-style: italic;"></span><span
|
||
|
|
style="font-style: italic;"></span> with the destination framebuffer
|
||
|
|
color value (dst). Standard ANSI C operators used.<br>
|
||
|
|
<br>
|
||
|
|
<table cellpadding="2" cellspacing="2" border="1"
|
||
|
|
style="text-align: left; width: 50%; margin-left: auto; margin-right: auto;">
|
||
|
|
<tbody>
|
||
|
|
<tr>
|
||
|
|
<td style="vertical-align: top;">LogicOp <span
|
||
|
|
style="font-style: italic;">mode</span><br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">Resulting channel value<br>
|
||
|
|
</td>
|
||
|
|
</tr>
|
||
|
|
<tr>
|
||
|
|
<td style="vertical-align: top;">GL_CLEAR<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">0<br>
|
||
|
|
</td>
|
||
|
|
</tr>
|
||
|
|
<tr>
|
||
|
|
<td style="vertical-align: top;">GL_SET<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">~0<br>
|
||
|
|
</td>
|
||
|
|
</tr>
|
||
|
|
<tr>
|
||
|
|
<td style="vertical-align: top;">GL_COPY<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">src<br>
|
||
|
|
</td>
|
||
|
|
</tr>
|
||
|
|
<tr>
|
||
|
|
<td style="vertical-align: top;">GL_COPY_INVERTED<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">~s<br>
|
||
|
|
</td>
|
||
|
|
</tr>
|
||
|
|
<tr>
|
||
|
|
<td style="vertical-align: top;">GL_NOOP<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">dst<br>
|
||
|
|
</td>
|
||
|
|
</tr>
|
||
|
|
<tr>
|
||
|
|
<td style="vertical-align: top;">GL_INVERT<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">~dst<br>
|
||
|
|
</td>
|
||
|
|
</tr>
|
||
|
|
<tr>
|
||
|
|
<td style="vertical-align: top;">GL_AND<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">src & dst<br>
|
||
|
|
</td>
|
||
|
|
</tr>
|
||
|
|
<tr>
|
||
|
|
<td style="vertical-align: top;">GL_NAND<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">~(src & dst)<br>
|
||
|
|
</td>
|
||
|
|
</tr>
|
||
|
|
<tr>
|
||
|
|
<td style="vertical-align: top;">GL_AND_REVERSE<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">src & ~dst<br>
|
||
|
|
</td>
|
||
|
|
</tr>
|
||
|
|
<tr>
|
||
|
|
<td style="vertical-align: top;">GL_AND_INVERTED<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">~src & dst<br>
|
||
|
|
</td>
|
||
|
|
</tr>
|
||
|
|
<tr>
|
||
|
|
<td style="vertical-align: top;">GL_OR<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">src | dst<br>
|
||
|
|
</td>
|
||
|
|
</tr>
|
||
|
|
<tr>
|
||
|
|
<td style="vertical-align: top;">GL_NOR<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">~(src | dst)<br>
|
||
|
|
</td>
|
||
|
|
</tr>
|
||
|
|
<tr>
|
||
|
|
<td style="vertical-align: top;">GL_OR_REVERSE<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">src | ~dst<br>
|
||
|
|
</td>
|
||
|
|
</tr>
|
||
|
|
<tr>
|
||
|
|
<td style="vertical-align: top;">GL_OR_INVERTED<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">~src | dst<br>
|
||
|
|
</td>
|
||
|
|
</tr>
|
||
|
|
<tr>
|
||
|
|
<td style="vertical-align: top;">GL_XOR<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">src ^ dst<br>
|
||
|
|
</td>
|
||
|
|
</tr>
|
||
|
|
<tr>
|
||
|
|
<td style="vertical-align: top;">GL_EQUIV<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">~(src ^ dst)<br>
|
||
|
|
</td>
|
||
|
|
</tr>
|
||
|
|
</tbody>
|
||
|
|
</table>
|
||
|
|
<br>
|
||
|
|
The fragment's color is replaced by the result of the logic operation.<br>
|
||
|
|
<br>
|
||
|
|
Specifying any value for <span style="font-style: italic;">mode</span>
|
||
|
|
other than those listed in the above table will cause the error
|
||
|
|
GL_INVALID_ENUM to be raised.<br>
|
||
|
|
<br>
|
||
|
|
The default value for <span style="font-style: italic;">mode</span> is
|
||
|
|
GL_COPY. The logic operation is disabled by default.<br>
|
||
|
|
<br>
|
||
|
|
<h3>6.4.2 Blending</h3>
|
||
|
|
The command<br>
|
||
|
|
<br>
|
||
|
|
<div style="margin-left: 40px;">void <span style="font-weight: bold;">glBlendFunc</span>(GLenum<span
|
||
|
|
style="font-style: italic;">srcTerm</span>, GLenum <span
|
||
|
|
style="font-style: italic;">dstTerm</span>)<br>
|
||
|
|
</div>
|
||
|
|
<br>
|
||
|
|
specifies the terms of the blending equation. If Cf = (Rf, Gf,
|
||
|
|
Bf, Af) is the incoming fragment color and Cb = (Rb, Gb, Bb, Ab) is the
|
||
|
|
frame buffer color, then the resulting color Cv = (Rv, Gv, Bv, Av) is
|
||
|
|
computed by:<br>
|
||
|
|
<br>
|
||
|
|
<div style="margin-left: 40px;">Cv = Cf * <span
|
||
|
|
style="font-style: italic;">srcTerm</span> + Cb * <span
|
||
|
|
style="font-style: italic;">dstTerm</span><br>
|
||
|
|
<span style="font-style: italic;"></span></div>
|
||
|
|
<span style="font-style: italic;"> </span><br>
|
||
|
|
All possible values for <span style="font-style: italic;">srcTerm</span>
|
||
|
|
and the corresponding arithmetic term are listed in the following table:<br>
|
||
|
|
<br>
|
||
|
|
<table cellpadding="2" cellspacing="2" border="1"
|
||
|
|
style="text-align: left; width: 70%; margin-left: auto; margin-right: auto;">
|
||
|
|
<tbody>
|
||
|
|
<tr>
|
||
|
|
<td style="vertical-align: top;"><span style="font-style: italic;">srcTerm</span><br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;"><span style="font-style: italic;">srcTerm</span>Arithmetic<br>
|
||
|
|
</td>
|
||
|
|
</tr>
|
||
|
|
<tr>
|
||
|
|
<td style="vertical-align: top;">GL_ZERO<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">(0, 0, 0, 0)<br>
|
||
|
|
</td>
|
||
|
|
</tr>
|
||
|
|
<tr>
|
||
|
|
<td style="vertical-align: top;">GL_ONE<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">(1, 1, 1, 1)<br>
|
||
|
|
</td>
|
||
|
|
</tr>
|
||
|
|
<tr>
|
||
|
|
<td style="vertical-align: top;">GL_DST_COLOR<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">(Rb, Gb, Bb, Ab)<br>
|
||
|
|
</td>
|
||
|
|
</tr>
|
||
|
|
<tr>
|
||
|
|
<td style="vertical-align: top;">GL_ONE_MINUS_DST_COLOR<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">(1-Rb, 1-Gb, 1-Bb, 1-Ab)<br>
|
||
|
|
</td>
|
||
|
|
</tr>
|
||
|
|
<tr>
|
||
|
|
<td style="vertical-align: top;">GL_SRC_ALPHA<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">(Af, Af, Af, AF)<br>
|
||
|
|
</td>
|
||
|
|
</tr>
|
||
|
|
<tr>
|
||
|
|
<td style="vertical-align: top;">GL_ONE_MINUS_SRC_ALPHA<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">(1-Af, 1-Af, 1-Af, 1-Af)<br>
|
||
|
|
</td>
|
||
|
|
</tr>
|
||
|
|
<tr>
|
||
|
|
<td style="vertical-align: top;">GL_DST_ALPHA<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">(Ab, Ab, Ab, Ab)<br>
|
||
|
|
</td>
|
||
|
|
</tr>
|
||
|
|
<tr>
|
||
|
|
<td style="vertical-align: top;">GL_ONE_MINUS_DST_ALPHA<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">(1-Ab, 1-Ab, 1-Ab, 1-Ab)<br>
|
||
|
|
</td>
|
||
|
|
</tr>
|
||
|
|
<tr>
|
||
|
|
<td style="vertical-align: top;">GL_SRC_ALPHA_SATURATE<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">(m, m, m, 1) where m = MIN(Af,
|
||
|
|
1-Ab)<br>
|
||
|
|
</td>
|
||
|
|
</tr>
|
||
|
|
</tbody>
|
||
|
|
</table>
|
||
|
|
<br>
|
||
|
|
All possible values for <span style="font-style: italic;">srcTerm</span>
|
||
|
|
and the corresponding arithmetic term are listed in the following table:<br>
|
||
|
|
<br>
|
||
|
|
<table cellpadding="2" cellspacing="2" border="1"
|
||
|
|
style="text-align: left; width: 70%; margin-left: auto; margin-right: auto;">
|
||
|
|
<tbody>
|
||
|
|
<tr>
|
||
|
|
<td style="vertical-align: top;"><span style="font-style: italic;">dstTerm</span><br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;"><span style="font-style: italic;">dstTerm</span>Arithmetic<br>
|
||
|
|
</td>
|
||
|
|
</tr>
|
||
|
|
<tr>
|
||
|
|
<td style="vertical-align: top;">GL_ZERO<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">(0, 0, 0, 0)<br>
|
||
|
|
</td>
|
||
|
|
</tr>
|
||
|
|
<tr>
|
||
|
|
<td style="vertical-align: top;">GL_ONE<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">(1, 1, 1, 1)<br>
|
||
|
|
</td>
|
||
|
|
</tr>
|
||
|
|
<tr>
|
||
|
|
<td style="vertical-align: top;">GL_SRC_COLOR<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">(Rf, Gf, Bf, Af)<br>
|
||
|
|
</td>
|
||
|
|
</tr>
|
||
|
|
<tr>
|
||
|
|
<td style="vertical-align: top;">GL_ONE_MINUS_SRC_COLOR<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">(1-Rf, 1-Gf, 1-Bf, 1-Af)<br>
|
||
|
|
</td>
|
||
|
|
</tr>
|
||
|
|
<tr>
|
||
|
|
<td style="vertical-align: top;">GL_SRC_ALPHA<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">(Af, Af, Af, AF)<br>
|
||
|
|
</td>
|
||
|
|
</tr>
|
||
|
|
<tr>
|
||
|
|
<td style="vertical-align: top;">GL_ONE_MINUS_SRC_ALPHA<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">(1-Af, 1-Af, 1-Af, 1-Af)<br>
|
||
|
|
</td>
|
||
|
|
</tr>
|
||
|
|
<tr>
|
||
|
|
<td style="vertical-align: top;">GL_DST_ALPHA<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">(Ab, Ab, Ab, Ab)<br>
|
||
|
|
</td>
|
||
|
|
</tr>
|
||
|
|
<tr>
|
||
|
|
<td style="vertical-align: top;">GL_ONE_MINUS_DST_ALPHA<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">(1-Ab, 1-Ab, 1-Ab, 1-Ab)<br>
|
||
|
|
</td>
|
||
|
|
</tr>
|
||
|
|
</tbody>
|
||
|
|
</table>
|
||
|
|
<br>
|
||
|
|
The fragment's color is replaced by the result of the blending equation.<br>
|
||
|
|
<br>
|
||
|
|
Values for <span style="font-style: italic;">srcTerm</span> and <span
|
||
|
|
style="font-style: italic;">dstTerm</span> other than those listed in
|
||
|
|
the table will cause the error GL_INVALID_ENUM to be raised.<br>
|
||
|
|
<br>
|
||
|
|
The default value for <span style="font-style: italic;">srcTerm</span>
|
||
|
|
is GL_ONE. The default value for <span style="font-style: italic;">dstTerm</span>
|
||
|
|
is GL_ZERO. Blending is disabled by default.<br>
|
||
|
|
<br>
|
||
|
|
<h2>6.5 Color Mask</h2>
|
||
|
|
The final fragment color is written into the current color buffer at
|
||
|
|
the end of the per-fragment operations. Normally, all color
|
||
|
|
channels in the frame buffer are replaced with the final fragment color.
|
||
|
|
However, the command<br>
|
||
|
|
<br>
|
||
|
|
<div style="margin-left: 40px;">void <span style="font-weight: bold;">glColorMask</span>(GLboolean<span
|
||
|
|
style="font-style: italic;">redMask</span>, GLboolean <span
|
||
|
|
style="font-style: italic;">greenMask</span>, GLboolean <span
|
||
|
|
style="font-style: italic;">blueMask</span>, GLboolean <span
|
||
|
|
style="font-style: italic;">alphaMask</span>)<br>
|
||
|
|
</div>
|
||
|
|
<br>
|
||
|
|
allows selective writing to individual color channels. If <span
|
||
|
|
style="font-style: italic;">redMask</span> is GL_TRUE then writing to
|
||
|
|
the red color channel is enabled, otherwise it's disabled.
|
||
|
|
Similarly, the green, blue and alpha channels can also be masked.<br>
|
||
|
|
<br>
|
||
|
|
Initially all four mask values are GL_TRUE.<br>
|
||
|
|
<br>
|
||
|
|
Color masking is not enabled/disabled with the <span
|
||
|
|
style="font-weight: bold;">glEnable</span>/<span
|
||
|
|
style="font-weight: bold;">glDisable</span> commands.<br>
|
||
|
|
<br>
|
||
|
|
<h1>7. Frame Buffer Operations</h1>
|
||
|
|
The frame buffer is considered to be a two-dimensional array of pixels.
|
||
|
|
The frame buffer is also organized into layers or logical buffers.
|
||
|
|
There may be a front color buffer, back color buffer and stencil
|
||
|
|
buffer. A double-buffered frame buffer has both a front color
|
||
|
|
buffer and back color buffer. A single-buffered framebuffer only
|
||
|
|
has a front color buffer. Each pixel in a color buffer has a red,
|
||
|
|
green and blue value and an optional alpha value.<br>
|
||
|
|
<br>
|
||
|
|
<h2>7.1 Clearing Buffers</h2>
|
||
|
|
Buffers are cleared (set to uniform values) with the command<br>
|
||
|
|
<br>
|
||
|
|
<div style="margin-left: 40px;">void <span style="font-weight: bold;">glClear</span>(GLbitfield<span
|
||
|
|
style="font-style: italic;">buffers</span>)<br>
|
||
|
|
</div>
|
||
|
|
<br>
|
||
|
|
<span style="font-style: italic;">buffers</span> is a bitmask for which
|
||
|
|
the value may be the bitwise-OR of the values GL_COLOR_BUFFER_BIT and
|
||
|
|
GL_STENCIL_BUFFER_BIT. If the GL_COLOR_BUFFER_BIT bit is
|
||
|
|
specified, the current color buffer will be cleared. If the
|
||
|
|
GL_STENCIL_BUFFER_BIT bit is specified, the stencil buffer will be
|
||
|
|
cleared.<br>
|
||
|
|
<br>
|
||
|
|
The current color buffer is specified with the command<br>
|
||
|
|
<br>
|
||
|
|
<div style="margin-left: 40px;">void <span style="font-weight: bold;">glDrawBuffer</span>(GLenum<span
|
||
|
|
style="font-style: italic;"> buffer</span>)<br>
|
||
|
|
</div>
|
||
|
|
<br>
|
||
|
|
<span style="font-style: italic;">buffer</span> may be either GL_FRONT,
|
||
|
|
GL_BACK or GL_NONE. GL_FRONT indicates that the front color buffer
|
||
|
|
will be modified by <span style="font-weight: bold;">glClear</span> and
|
||
|
|
any drawing command. GL_BACK indicates that the back color buffer
|
||
|
|
will be modified by <span style="font-weight: bold;">glClear</span> and
|
||
|
|
any drawing command. GL_NONE indicates that neither color buffer
|
||
|
|
will be modified by <span style="font-weight: bold;">glClear</span> or
|
||
|
|
any drawing command. GL_BACK is only valid for double-buffered
|
||
|
|
frame buffers.<br>
|
||
|
|
<br>
|
||
|
|
The current scissor rectangle, set by the <span
|
||
|
|
style="font-weight: bold;">glScissor</span> command, effects <span
|
||
|
|
style="font-weight: bold;">glClear</span><span
|
||
|
|
style="font-style: italic;">,</span><span style="font-style: italic;"> </span>limiting
|
||
|
|
the clear to the scissor rectangle, if it's enabled. Furthermore, <span
|
||
|
|
style="font-weight: bold;"></span>only the color channels enabled by <span
|
||
|
|
style="font-weight: bold;">glColorMask</span> will be effected by <span
|
||
|
|
style="font-weight: bold;">glClear</span>(GL_COLOR_BUFFER_BIT).
|
||
|
|
Likewise, only the stencil bits enabled by <span
|
||
|
|
style="font-weight: bold;">glStencilMask</span> will be effected by <span
|
||
|
|
style="font-weight: bold;">glClear</span>(GL_STENCIL_BUFFER_BIT).<br>
|
||
|
|
<br>
|
||
|
|
The current clear color is set with the command<br>
|
||
|
|
<br>
|
||
|
|
<div style="margin-left: 40px;">void <span style="font-weight: bold;">glClearColor</span>(GLclampf<span
|
||
|
|
style="font-style: italic;">red</span>, GLclampf <span
|
||
|
|
style="font-style: italic;">green</span>, GLclampf <span
|
||
|
|
style="font-style: italic;">blue</span>, GLclampf <span
|
||
|
|
style="font-style: italic;">alpha</span>)<br>
|
||
|
|
</div>
|
||
|
|
<br>
|
||
|
|
Subsequent calls to <span style="font-weight: bold;">glClear</span>
|
||
|
|
will use the color (<span style="font-style: italic;">red, green, blue,
|
||
|
|
alpha</span>) to clear the front or back color buffers.<br>
|
||
|
|
<span style="font-style: italic;"></span><br>
|
||
|
|
The current stencil clear value is set with the command<br>
|
||
|
|
<br>
|
||
|
|
<div style="margin-left: 40px;">void <span style="font-weight: bold;">glClearStencil</span>(GLint<span
|
||
|
|
style="font-style: italic;">clearValue</span>)<br>
|
||
|
|
</div>
|
||
|
|
<br>
|
||
|
|
If the stencil buffer is N bits deep, the least significant N bits of <span
|
||
|
|
style="font-style: italic;">clearValue</span> will be used to clear the
|
||
|
|
stencil buffer.<br>
|
||
|
|
<br>
|
||
|
|
<br>
|
||
|
|
<h1>8. Other Features</h1>
|
||
|
|
<h2>8.1 Frame Buffer Readback</h2>
|
||
|
|
A rectangular region of pixels can be read from the frame buffer and
|
||
|
|
placed in client memory with the command<br>
|
||
|
|
<br>
|
||
|
|
<div style="margin-left: 40px;">void <span style="font-weight: bold;">glReadPixels</span>(GLint<span
|
||
|
|
style="font-style: italic;">x</span>, GLint <span
|
||
|
|
style="font-style: italic;">y</span>, GLsizei <span
|
||
|
|
style="font-style: italic;">width</span>, GLsizei <span
|
||
|
|
style="font-style: italic;">height</span>, GLenum <span
|
||
|
|
style="font-style: italic;">format</span>, GLenum <span
|
||
|
|
style="font-style: italic;">type</span>, GLvoid *<span
|
||
|
|
style="font-style: italic;">data</span>)<br>
|
||
|
|
</div>
|
||
|
|
<br>
|
||
|
|
<span style="font-style: italic;">x</span> and <span
|
||
|
|
style="font-style: italic;">y</span> specify the coordinate of the
|
||
|
|
lower-left corner of the region to read and <span
|
||
|
|
style="font-style: italic;">width</span> and <span
|
||
|
|
style="font-style: italic;">height</span> specify the size of the
|
||
|
|
rectangular region to read. <span style="font-style: italic;">format</span>
|
||
|
|
specifies the format of image data and must be either GL_RGB or
|
||
|
|
GL_RGBA. <span style="font-style: italic;">type</span> specify the
|
||
|
|
data type of the image data and must be either GL_UNSIGNED_BYTE or
|
||
|
|
GL_FLOAT. Other values for <span style="font-style: italic;">format</span>
|
||
|
|
or <span style="font-style: italic;">type</span> will cause the error
|
||
|
|
GL_INVALID_ENUM to be raised.<br>
|
||
|
|
<br>
|
||
|
|
The framebuffer may contain 3-component colors (red, green, blue) or
|
||
|
|
4-component colors (red, green, blue, alpha). If an alpha channel
|
||
|
|
is not present, alpha values default to 1.0.<br>
|
||
|
|
<br>
|
||
|
|
The frame buffer color components (red, green, blue, alpha) are either
|
||
|
|
converted to 8-bit unsigned integers in the range[0, 255] if <span
|
||
|
|
style="font-style: italic;">type </span>is GL_UNSIGNED_BYTE or
|
||
|
|
converted to floating point values in the range [0, 1] if <span
|
||
|
|
style="font-style: italic;">type</span> is GL_FLOAT. The (red,
|
||
|
|
green, blue, alpha) tuples are then stored as GL_RGB triplets (by
|
||
|
|
dropping the alpha component) or GL_RGBA quadruples in client memory.<br>
|
||
|
|
<br>
|
||
|
|
Image data is <span style="font-style: italic;">packed</span> into
|
||
|
|
client memory according to the pixel packing parameters which are set by
|
||
|
|
the command<br>
|
||
|
|
<br>
|
||
|
|
<div style="margin-left: 40px;">void <span style="font-weight: bold;">glPixelStorei</span>(GLenum<span
|
||
|
|
style="font-style: italic;"> pname</span>, GLint <span
|
||
|
|
style="font-style: italic;">value</span>)<br>
|
||
|
|
</div>
|
||
|
|
<br>
|
||
|
|
<span style="font-style: italic;">pname</span> must be
|
||
|
|
GL_PACK_ROW_LENGTH. <span style="font-style: italic;">value</span>
|
||
|
|
indicates the stride (in pixels) between subsequent rows in the
|
||
|
|
destination image. If GL_PACK_ROW_LENGTH is zero (the default)
|
||
|
|
then the <span style="font-style: italic;">width</span> parameter to <span
|
||
|
|
style="font-weight: bold;">glReadPixels</span> indicates the row stride.<br>
|
||
|
|
<br>
|
||
|
|
Pixel readback takes place as follows:<br>
|
||
|
|
<br>
|
||
|
|
<div style="margin-left: 40px;">if (GL_PACK_ROW_LENGTH == 0)<br>
|
||
|
|
rowLength = <span style="font-style: italic;">width</span>;<br>
|
||
|
|
else<br>
|
||
|
|
rowLength = GL_PACK_ROW_LENGTH<br>
|
||
|
|
<br>
|
||
|
|
if (<span style="font-style: italic;">format</span> == GL_RGB) {<br>
|
||
|
|
for (i = 0; i < <span style="font-style: italic;">height</span>;
|
||
|
|
i++) {<br>
|
||
|
|
for (j = 0; j < <span
|
||
|
|
style="font-style: italic;">width</span>; j++) {<br>
|
||
|
|
k = (i *
|
||
|
|
rowLength + j) * 3;<br>
|
||
|
|
<span
|
||
|
|
style="font-style: italic;">data</span>[k+0] = FrameBuffer(<span
|
||
|
|
style="font-style: italic;">x</span> + j, <span
|
||
|
|
style="font-style: italic;">y</span> + i).red;<br>
|
||
|
|
<span
|
||
|
|
style="font-style: italic;">data</span>[k+1] = FrameBuffer(<span
|
||
|
|
style="font-style: italic;">x</span> + j, <span
|
||
|
|
style="font-style: italic;">y</span> + i).green;<br>
|
||
|
|
<span
|
||
|
|
style="font-style: italic;">data</span>[k+2] = FrameBuffer(<span
|
||
|
|
style="font-style: italic;">x</span> + j, <span
|
||
|
|
style="font-style: italic;">y</span> + i).blue;<span
|
||
|
|
style="font-style: italic;"></span><br>
|
||
|
|
}<br>
|
||
|
|
}<br>
|
||
|
|
}<br>
|
||
|
|
else {<br>
|
||
|
|
for (i = 0; i < <span style="font-style: italic;">height</span>;
|
||
|
|
i++) {<br>
|
||
|
|
for (j = 0; j < <span
|
||
|
|
style="font-style: italic;">width</span>; j++) {<br>
|
||
|
|
k = (i *
|
||
|
|
rowLength + j) * 4;<br>
|
||
|
|
<span
|
||
|
|
style="font-style: italic;">data</span>[k+0] = FrameBuffer(<span
|
||
|
|
style="font-style: italic;">x</span> + j, <span
|
||
|
|
style="font-style: italic;">y</span> + i).red;<br>
|
||
|
|
<span
|
||
|
|
style="font-style: italic;">data</span>[k+1] = FrameBuffer(<span
|
||
|
|
style="font-style: italic;">x</span> + j, <span
|
||
|
|
style="font-style: italic;">y</span> + i).green;<br>
|
||
|
|
<span
|
||
|
|
style="font-style: italic;">data</span>[k+2] = FrameBuffer(<span
|
||
|
|
style="font-style: italic;">x</span> + j, <span
|
||
|
|
style="font-style: italic;">y</span> + i).blue;<span
|
||
|
|
style="font-style: italic;"></span><br>
|
||
|
|
<span
|
||
|
|
style="font-style: italic;">data</span>[k+3] = FrameBuffer(<span
|
||
|
|
style="font-style: italic;">x</span> + j, <span
|
||
|
|
style="font-style: italic;">y</span> + i).alpha;<span
|
||
|
|
style="font-style: italic;"></span><br>
|
||
|
|
}<br>
|
||
|
|
}<br>
|
||
|
|
}<br>
|
||
|
|
</div>
|
||
|
|
<br>
|
||
|
|
The function FrameBuffer(<span style="font-style: italic;">c, r</span>)
|
||
|
|
returns the pixel in the frame buffer at column <span
|
||
|
|
style="font-style: italic;">c</span> of row <span
|
||
|
|
style="font-style: italic;">r. </span><span
|
||
|
|
style="font-style: italic;">data</span> is considered to be either a
|
||
|
|
GLubyte pointer or a GLfloat pointer, depending on the <span
|
||
|
|
style="font-style: italic;">type</span> parameter. Similarly, the
|
||
|
|
FrameBuffer function returns either GLubyte values in the range [0, 255]
|
||
|
|
or GLfloat values in the range [0,1], depending on the <span
|
||
|
|
style="font-style: italic;">type</span> parameter.<br>
|
||
|
|
<br>
|
||
|
|
Pixels may be read from either the front or back color buffer.
|
||
|
|
The command<br>
|
||
|
|
<br>
|
||
|
|
<div style="margin-left: 40px;">void <span style="font-weight: bold;">glReadBuffer</span>(GLenum<span
|
||
|
|
style="font-style: italic;">buffer</span>)<br>
|
||
|
|
</div>
|
||
|
|
<br>
|
||
|
|
specifies the source for reading images with <span
|
||
|
|
style="font-weight: bold;">glReadPixels</span>. If <span
|
||
|
|
style="font-style: italic;">buffer</span> is GL_FRONT then front color
|
||
|
|
buffer is the source. If <span style="font-style: italic;">buffer</span>
|
||
|
|
is GL_BACK then the back color buffer is the source. It is illegal
|
||
|
|
to specify GL_BACK when the color buffer is not double buffered.
|
||
|
|
Any invalid value for <span style="font-style: italic;">buffer</span>
|
||
|
|
will raise the error GL_INVALID_ENUM.<br>
|
||
|
|
<br>
|
||
|
|
The default read source is GL_BACK if the frame buffer is double
|
||
|
|
buffered. Otherwise, the default read source is GL_FRONT.<br>
|
||
|
|
<br>
|
||
|
|
<h2>8.2 Selection Mode</h2>
|
||
|
|
Selection mode is typically used to implement <span
|
||
|
|
style="font-style: italic;">picking</span>: determining which
|
||
|
|
primitive(s) are present at particular window positions. The
|
||
|
|
command<br>
|
||
|
|
<br>
|
||
|
|
<div style="margin-left: 40px;">GLint <span style="font-weight: bold;">glRenderMode</span>(GLenum<span
|
||
|
|
style="font-style: italic;">mode</span>)<br>
|
||
|
|
</div>
|
||
|
|
<br>
|
||
|
|
is used to enable selection mode. If <span
|
||
|
|
style="font-style: italic;">mode</span> is GL_SELECTION the graphics
|
||
|
|
library is put into selection mode. If <span
|
||
|
|
style="font-style: italic;">mode</span> is GL_RENDER the graphic
|
||
|
|
library is put into normal rendering mode. Any other value for <span
|
||
|
|
style="font-style: italic;">mode</span> will raise the error
|
||
|
|
GL_INVALID_ENUM.<br>
|
||
|
|
<br>
|
||
|
|
When in selection mode rendering commands will not effect the
|
||
|
|
framebuffer. Instead, a record of the primitives that would have
|
||
|
|
been drawn is placed in the <span style="font-style: italic;">selection</span> <span
|
||
|
|
style="font-style: italic;">buffer</span>. The selection buffer
|
||
|
|
is specified with the command<br>
|
||
|
|
<br>
|
||
|
|
<div style="margin-left: 40px;">void <span style="font-weight: bold;">glSelectionBuffer</span>(GLsizei<span
|
||
|
|
style="font-style: italic;">n</span>, GLuint *<span
|
||
|
|
style="font-style: italic;">buffer</span>)<br>
|
||
|
|
</div>
|
||
|
|
<span style="font-style: italic;"></span><span
|
||
|
|
style="font-style: italic;"><br>
|
||
|
|
buffer</span> is an array of <span style="font-style: italic;">n</span>
|
||
|
|
unsigned integers. No more than <span style="font-style: italic;">n</span>
|
||
|
|
values will be placed in the buffer.<br>
|
||
|
|
<br>
|
||
|
|
The <span style="font-style: italic;">name stack</span> is a stack
|
||
|
|
(LIFO) of unsigned integer names. The following commands
|
||
|
|
manipulate the name stack:<br>
|
||
|
|
<br>
|
||
|
|
<div style="margin-left: 40px;">void <span style="font-weight: bold;">glInitNames</span>(void)<br>
|
||
|
|
void <span style="font-weight: bold;">glPushName</span>(GLuint <span
|
||
|
|
style="font-style: italic;">name</span>)<br>
|
||
|
|
void <span style="font-weight: bold;">glPopName</span>(void)<br>
|
||
|
|
void <span style="font-weight: bold;">glLoadName</span>(GLuint <span
|
||
|
|
style="font-style: italic;">name</span>)<br>
|
||
|
|
</div>
|
||
|
|
<br>
|
||
|
|
<span style="font-weight: bold;">glInitNames</span> resets the name
|
||
|
|
stack to an empty state. <span style="font-weight: bold;">glPushName<span
|
||
|
|
style="font-style: italic;"> </span></span>pushes the given <span
|
||
|
|
style="font-style: italic;">name</span> value onto the stack. <span
|
||
|
|
style="font-weight: bold;">glPopName</span> pops the top name from the
|
||
|
|
stack. <span style="font-weight: bold;">glLoadName<span
|
||
|
|
style="font-style: italic;"> </span></span>replaces the top value on
|
||
|
|
the stack with the specified <span style="font-style: italic;">name</span>.
|
||
|
|
Stack underflow and overflow conditions cause the errors
|
||
|
|
GL_STACK_OVERFLOW and GL_STACK_UNDERFLOW to be raised.<br>
|
||
|
|
<br>
|
||
|
|
While in selection mode, primitives (points, lines, polygons) are
|
||
|
|
transformed and clip-tested normally. Primitives which aren't
|
||
|
|
discarded by clipping cause the <span style="font-style: italic;">hit</span> <span
|
||
|
|
style="font-style: italic;">data</span> to be updated. The hit
|
||
|
|
data consists of three pieces of information: a hit flag, a minimum Z
|
||
|
|
value and a maximum Z value. First, the hit flag is set.
|
||
|
|
Then, for each of the primitive's vertices, the vertex Z value is
|
||
|
|
compared to the minimum and maximum Z values. The minimum Z value
|
||
|
|
is updated if the vertex's Z value is less than the minimum Z value.
|
||
|
|
The maximum Z value is updated if the vertex's Z value is greater
|
||
|
|
than the maximum Z value.<br>
|
||
|
|
<br>
|
||
|
|
When any of <span style="font-weight: bold;">glInitNames</span><span
|
||
|
|
style="font-style: italic;"><span style="font-style: italic;">, </span></span><span
|
||
|
|
style="font-weight: bold;">glPushName</span>, <span
|
||
|
|
style="font-weight: bold;">glPopName</span>, <span
|
||
|
|
style="font-weight: bold;">glLoadName</span> or <span
|
||
|
|
style="font-weight: bold;">glRenderMode</span> are called and the hit
|
||
|
|
flag is set, a <span style="font-style: italic;">hit record</span> is
|
||
|
|
written to the selection buffer.<br>
|
||
|
|
<br>
|
||
|
|
A hit record consists of a sequence of unsigned integers. The
|
||
|
|
first value is the size of the name stack. The second value is the
|
||
|
|
minimum Z value multiplied by 2<sup>32</sup>-1. The third value is
|
||
|
|
the maximum Z value multiplied by 2<sup>32</sup>-1. The remaining
|
||
|
|
values are the values in the name stack, in bottom to top order.
|
||
|
|
The hit flag is cleared after a hit record is written to the
|
||
|
|
selection buffer. Hit records are places sequentially into the
|
||
|
|
selection buffer until it is full or selection mode is terminated.<br>
|
||
|
|
<br>
|
||
|
|
Selection mode is terminated by calling <span
|
||
|
|
style="font-weight: bold;">glRenderMode</span>(GL_RENDER). The
|
||
|
|
return value of <span style="font-weight: bold;">glRenderMode</span>
|
||
|
|
will be -1 if the selection buffer overflowed. Otherwise, the
|
||
|
|
return value will indicate the number of values written into the
|
||
|
|
selection buffer.<br>
|
||
|
|
<br>
|
||
|
|
<h2>8.3 Synchronization</h2>
|
||
|
|
The command<br>
|
||
|
|
<br>
|
||
|
|
<div style="margin-left: 40px;">void <span style="font-weight: bold;">glFlush</span>(void)<br>
|
||
|
|
</div>
|
||
|
|
<br>
|
||
|
|
makes the graphics library to flush all pending graphics commands.
|
||
|
|
The command<br>
|
||
|
|
<div style="margin-left: 40px;"><br>
|
||
|
|
void <span style="font-weight: bold;">glFinish</span>(void)<br>
|
||
|
|
</div>
|
||
|
|
<br>
|
||
|
|
makes the graphics library flush the command queue and wait until those
|
||
|
|
commands are completed. <span style="font-weight: bold;">glFlush</span>
|
||
|
|
will not return until all previous graphics commands have been fully
|
||
|
|
completed.<br>
|
||
|
|
<br>
|
||
|
|
These commands are typically used to force completion of rendering to
|
||
|
|
the front color buffer. Otherwise, rendering to the front color
|
||
|
|
buffer may not appear. The <span style="font-style: italic;">swapbuffers</span>
|
||
|
|
command (part of the window system binding library) does an implicit
|
||
|
|
flush before swapping the front and back color buffers. The <span
|
||
|
|
style="font-weight: bold;">glReadPixels</span> command also does an
|
||
|
|
implicit flush before reading pixel data from the frame buffer.<br>
|
||
|
|
<br>
|
||
|
|
<h1>9. State Queries</h1>
|
||
|
|
The current value of nearly all library state variables can be queried.
|
||
|
|
This chapter describes the commands used for querying the value of
|
||
|
|
state variables.<br>
|
||
|
|
<br>
|
||
|
|
<h2>9.1 General State Queries</h2>
|
||
|
|
The command<br>
|
||
|
|
<br>
|
||
|
|
<div style="margin-left: 40px;">void <span style="font-weight: bold;">glGetFloatv</span>(GLenum<span
|
||
|
|
style="font-style: italic;">pname</span>, GLfloat *<span
|
||
|
|
style="font-style: italic;">values</span>)<br>
|
||
|
|
</div>
|
||
|
|
<br>
|
||
|
|
returns the value(s) of the state variable specified by <span
|
||
|
|
style="font-style: italic;">pname</span>. The following table
|
||
|
|
lists all accepted values for <span style="font-style: italic;">pname</span>
|
||
|
|
and a description of the value(s). Specifying any other value for <span
|
||
|
|
style="font-style: italic;">pname</span> causes the error
|
||
|
|
GL_INVALID_ENUM to be raised.<br>
|
||
|
|
<br>
|
||
|
|
<table cellpadding="2" cellspacing="2" border="1"
|
||
|
|
style="text-align: left; width: 90%; margin-left: auto; margin-right: auto;">
|
||
|
|
<tbody>
|
||
|
|
<tr>
|
||
|
|
<td style="vertical-align: top;">Variable (<span
|
||
|
|
style="font-style: italic;">pname)</span><br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">Number of values<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">Value(s) Description<br>
|
||
|
|
</td>
|
||
|
|
</tr>
|
||
|
|
<tr>
|
||
|
|
<td style="vertical-align: top;">GL_ALPHA_BITS<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">1<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">Number of bits per alpha value
|
||
|
|
in the frame buffer.<br>
|
||
|
|
</td>
|
||
|
|
</tr>
|
||
|
|
<tr>
|
||
|
|
<td style="vertical-align: top;">GL_ALPHA_TEST<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">1<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">Zero if the alpha test is
|
||
|
|
disabled.<br>
|
||
|
|
One if the alpha test is enabled.<br>
|
||
|
|
</td>
|
||
|
|
</tr>
|
||
|
|
<tr>
|
||
|
|
<td style="vertical-align: top;">GL_ALPHA_TEST_FUNC<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">1<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">The alpha test function.<br>
|
||
|
|
</td>
|
||
|
|
</tr>
|
||
|
|
<tr>
|
||
|
|
<td style="vertical-align: top;">GL_BLEND<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">1<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">Zero if blending is disabled.<br>
|
||
|
|
One if blending is enabled.<br>
|
||
|
|
</td>
|
||
|
|
</tr>
|
||
|
|
<tr>
|
||
|
|
<td style="vertical-align: top;">GL_BLEND_DST<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">1<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">Blend destination function/term.<br>
|
||
|
|
</td>
|
||
|
|
</tr>
|
||
|
|
<tr>
|
||
|
|
<td style="vertical-align: top;">GL_BLEND_SRC<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">1<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">Blend source function/term.<br>
|
||
|
|
</td>
|
||
|
|
</tr>
|
||
|
|
<tr>
|
||
|
|
<td style="vertical-align: top;">GL_BLUE_BITS<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">1<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">Number of bits per blue value in
|
||
|
|
the frame buffer.<br>
|
||
|
|
</td>
|
||
|
|
</tr>
|
||
|
|
<tr>
|
||
|
|
<td style="vertical-align: top;">GL_COLOR_CLEAR_VALUE<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">4<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">Clear color (red, green, blue,
|
||
|
|
alpha).<br>
|
||
|
|
</td>
|
||
|
|
</tr>
|
||
|
|
<tr>
|
||
|
|
<td style="vertical-align: top;">GL_COLOR_WRITE_MASK<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">4<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">Color buffer writemask (red,
|
||
|
|
green, blue, alpha).<br>
|
||
|
|
Zero if writing is disabled.<br>
|
||
|
|
One if writing is enabled.<br>
|
||
|
|
</td>
|
||
|
|
</tr>
|
||
|
|
<tr>
|
||
|
|
<td style="vertical-align: top;">GL_CULL_FACE<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">1<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">Zero if polygon culling is
|
||
|
|
disabled.<br>
|
||
|
|
One if polygon culling is enabled.<br>
|
||
|
|
</td>
|
||
|
|
</tr>
|
||
|
|
<tr>
|
||
|
|
<td style="vertical-align: top;">GL_CULL_FACE_MODE<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">1<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">Polygon cull mode: GL_FRONT,
|
||
|
|
GL_BACK or GL_FRONT_AND_BACK.<br>
|
||
|
|
</td>
|
||
|
|
</tr>
|
||
|
|
<tr>
|
||
|
|
<td style="vertical-align: top;">GL_CURRENT_COLOR<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">4<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">Current color (red, green, blue,
|
||
|
|
alpha).<br>
|
||
|
|
</td>
|
||
|
|
</tr>
|
||
|
|
<tr>
|
||
|
|
<td style="vertical-align: top;">GL_CURRENT_RASTER_COLOR<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">4<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">Current raster position color
|
||
|
|
(red, green, blue, alpha).<br>
|
||
|
|
</td>
|
||
|
|
</tr>
|
||
|
|
<tr>
|
||
|
|
<td style="vertical-align: top;">GL_CURRENT_RASTER_TEXTURE_COORDS<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">4<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">Current raster position texture
|
||
|
|
coordinates (s, t, r, q).<br>
|
||
|
|
</td>
|
||
|
|
</tr>
|
||
|
|
<tr>
|
||
|
|
<td style="vertical-align: top;">GL_CURRENT_RASTER_POSITION<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">4<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">Current raster position (x, y,
|
||
|
|
z, w).<br>
|
||
|
|
</td>
|
||
|
|
</tr>
|
||
|
|
<tr>
|
||
|
|
<td style="vertical-align: top;">GL_CURRENT_POSITION_VALID<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">1<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">Zero if current raster position
|
||
|
|
is invalid.<br>
|
||
|
|
One if current raster position is valid.<br>
|
||
|
|
</td>
|
||
|
|
</tr>
|
||
|
|
<tr>
|
||
|
|
<td style="vertical-align: top;">GL_CURRENT_TEXTURE_COORDS<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">4<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">Current texture coordinates (s,
|
||
|
|
t, r, q)<br>
|
||
|
|
</td>
|
||
|
|
</tr>
|
||
|
|
<tr>
|
||
|
|
<td style="vertical-align: top;">GL_DOUBLEBUFFER<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">1<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">Zero if color buffer is
|
||
|
|
single-buffered.<br>
|
||
|
|
One if color buffer is double-buffered.<br>
|
||
|
|
</td>
|
||
|
|
</tr>
|
||
|
|
<tr>
|
||
|
|
<td style="vertical-align: top;">GL_DRAW_BUFFER<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">1<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">Current color draw buffer:
|
||
|
|
GL_FRONT or GL_BACK.<br>
|
||
|
|
</td>
|
||
|
|
</tr>
|
||
|
|
<tr>
|
||
|
|
<td style="vertical-align: top;">GL_FRONT_FACE</td>
|
||
|
|
<td style="vertical-align: top;">1<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">Polygon front-face winding:
|
||
|
|
GL_CW or GL_CCW.<br>
|
||
|
|
</td>
|
||
|
|
</tr>
|
||
|
|
<tr>
|
||
|
|
<td style="vertical-align: top;">GL_GREEN_BITS<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">1<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">Number of bits per green value
|
||
|
|
in the frame buffer.<br>
|
||
|
|
</td>
|
||
|
|
</tr>
|
||
|
|
<tr>
|
||
|
|
<td style="vertical-align: top;">GL_LINE_SMOOTH<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">1<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">Zero if line smoothing is
|
||
|
|
disabled.<br>
|
||
|
|
One if line smoothing is enabled.<br>
|
||
|
|
</td>
|
||
|
|
</tr>
|
||
|
|
<tr>
|
||
|
|
<td style="vertical-align: top;">GL_LINE_STIPPLE<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">1<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">Zero if line stippling is
|
||
|
|
disabled.<br>
|
||
|
|
One if line stippling is enabled.<br>
|
||
|
|
</td>
|
||
|
|
</tr>
|
||
|
|
<tr>
|
||
|
|
<td style="vertical-align: top;">GL_LINE_STIPPLE_PATTERN<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">1<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">Line stipple pattern.<br>
|
||
|
|
</td>
|
||
|
|
</tr>
|
||
|
|
<tr>
|
||
|
|
<td style="vertical-align: top;">GL_LINE_STIPPLE_REPEAT<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">1<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">Line stipple repeat factor.<br>
|
||
|
|
</td>
|
||
|
|
</tr>
|
||
|
|
<tr>
|
||
|
|
<td style="vertical-align: top;">GL_LINE_WIDTH<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">1<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">Line width in pixels.<br>
|
||
|
|
</td>
|
||
|
|
</tr>
|
||
|
|
<tr>
|
||
|
|
<td style="vertical-align: top;">GL_LINE_WIDTH_GRANULARITY<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">1<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">Aliased line width granularity.<br>
|
||
|
|
</td>
|
||
|
|
</tr>
|
||
|
|
<tr>
|
||
|
|
<td style="vertical-align: top;">GL_LINE_WIDTH_RANGE<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">2<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">Minimum and maximum aliased line
|
||
|
|
widths.<br>
|
||
|
|
</td>
|
||
|
|
</tr>
|
||
|
|
<tr>
|
||
|
|
<td style="vertical-align: top;">GL_ALIASED_LINE_WIDTH_RANGE<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">2<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">Minimum and maximum antialiased
|
||
|
|
line widths.</td>
|
||
|
|
</tr>
|
||
|
|
<tr>
|
||
|
|
<td style="vertical-align: top;">GL_COLOR_LOGIC_OP<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">1<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">Zero if logicop is disabled.<br>
|
||
|
|
One if logicop is enabled.<br>
|
||
|
|
</td>
|
||
|
|
</tr>
|
||
|
|
<tr>
|
||
|
|
<td style="vertical-align: top;">GL_LOGIC_OP_MODE<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">1<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">Logicop function.<br>
|
||
|
|
</td>
|
||
|
|
</tr>
|
||
|
|
<tr>
|
||
|
|
<td style="vertical-align: top;">GL_MATRIX_MODE<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">1<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">Matrix mode: GL_MODELVIEW or
|
||
|
|
GL_PROJECTION.<br>
|
||
|
|
</td>
|
||
|
|
</tr>
|
||
|
|
<tr>
|
||
|
|
<td style="vertical-align: top;">GL_MAX_MODELVIEW_STACK_DEPTH<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">1<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">Maximum size of the modelview
|
||
|
|
matrix stack.<br>
|
||
|
|
</td>
|
||
|
|
</tr>
|
||
|
|
<tr>
|
||
|
|
<td style="vertical-align: top;">GL_MAX_NAME_STACK_DEPTH<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">1<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">Maximum size of the selection
|
||
|
|
name stack.<br>
|
||
|
|
</td>
|
||
|
|
</tr>
|
||
|
|
<tr>
|
||
|
|
<td style="vertical-align: top;">GL_MAX_PROJECTION_STACK_DEPTH<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">1<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">Maximum size of the projection
|
||
|
|
matrix stack.<br>
|
||
|
|
</td>
|
||
|
|
</tr>
|
||
|
|
<tr>
|
||
|
|
<td style="vertical-align: top;">GL_MAX_TEXTURE_SIZE<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">1<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">Maximum 2D texture image width
|
||
|
|
and height.<br>
|
||
|
|
</td>
|
||
|
|
</tr>
|
||
|
|
<tr>
|
||
|
|
<td style="vertical-align: top;">GL_MAX_VIEWPORT_DIMS<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">2</td>
|
||
|
|
<td style="vertical-align: top;">Maximum viewport width and
|
||
|
|
height in pixels.<br>
|
||
|
|
</td>
|
||
|
|
</tr>
|
||
|
|
<tr>
|
||
|
|
<td style="vertical-align: top;">GL_MODELVIEW_MATRIX<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">16<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">Current/top modelview matrix
|
||
|
|
values.<br>
|
||
|
|
</td>
|
||
|
|
</tr>
|
||
|
|
<tr>
|
||
|
|
<td style="vertical-align: top;">GL_MODELVIEW_MATRIX_STACK_DEPTH<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">1<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">Current size of the modelview
|
||
|
|
matrix stack.<br>
|
||
|
|
</td>
|
||
|
|
</tr>
|
||
|
|
<tr>
|
||
|
|
<td style="vertical-align: top;">GL_NAME_STACK_DEPTH<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">1<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">Current size of the selection
|
||
|
|
name stack.<br>
|
||
|
|
</td>
|
||
|
|
</tr>
|
||
|
|
<tr>
|
||
|
|
<td style="vertical-align: top;">GL_PACK_ROW_LENGTH<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">1<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">Pixel packing row length.<br>
|
||
|
|
</td>
|
||
|
|
</tr>
|
||
|
|
<tr>
|
||
|
|
<td style="vertical-align: top;">GL_POLYGON_SMOOTH<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">1<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">Zero if polygon smoothing is
|
||
|
|
disabled.<br>
|
||
|
|
One if polygon smoothing is enabled.<br>
|
||
|
|
</td>
|
||
|
|
</tr>
|
||
|
|
<tr>
|
||
|
|
<td style="vertical-align: top;">GL_PROJECTION_MATRIX<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">16<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">Current/top projection matrix
|
||
|
|
values.<br>
|
||
|
|
</td>
|
||
|
|
</tr>
|
||
|
|
<tr>
|
||
|
|
<td style="vertical-align: top;">GL_PROJECTION_STACK_DEPTH<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">1<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">Current size of projection
|
||
|
|
matrix stack.<br>
|
||
|
|
</td>
|
||
|
|
</tr>
|
||
|
|
<tr>
|
||
|
|
<td style="vertical-align: top;">GL_READ_BUFFER<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">1<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">Current read buffer: GL_FRONT or
|
||
|
|
GL_BACK.<br>
|
||
|
|
</td>
|
||
|
|
</tr>
|
||
|
|
<tr>
|
||
|
|
<td style="vertical-align: top;">GL_RED_BITS<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">1<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">Number of bits per red value in
|
||
|
|
the frame buffer.<br>
|
||
|
|
</td>
|
||
|
|
</tr>
|
||
|
|
<tr>
|
||
|
|
<td style="vertical-align: top;">GL_RENDER_MODE<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">1<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">Current rendering mode:
|
||
|
|
GL_RENDER or GL_SELECTION.<br>
|
||
|
|
</td>
|
||
|
|
</tr>
|
||
|
|
<tr>
|
||
|
|
<td style="vertical-align: top;">GL_RGBA_MODE<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">1<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">Always one.<br>
|
||
|
|
</td>
|
||
|
|
</tr>
|
||
|
|
<tr>
|
||
|
|
<td style="vertical-align: top;">GL_SCISSOR_BOX<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">4<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">Scissor box (x, y, width,
|
||
|
|
height).<br>
|
||
|
|
</td>
|
||
|
|
</tr>
|
||
|
|
<tr>
|
||
|
|
<td style="vertical-align: top;">GL_SCISSOR_TEST<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">1<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">Zero if scissor test is disabled.<br>
|
||
|
|
One if scissor test is enabled.<br>
|
||
|
|
</td>
|
||
|
|
</tr>
|
||
|
|
<tr>
|
||
|
|
<td style="vertical-align: top;">GL_SELECTION_BUFFER_SIZE<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">1<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">Size of selection buffer.<br>
|
||
|
|
</td>
|
||
|
|
</tr>
|
||
|
|
<tr>
|
||
|
|
<td style="vertical-align: top;">GL_SHADE_MODEL<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">1<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">Shade model: GL_FLAT or
|
||
|
|
GL_SMOOTH.<br>
|
||
|
|
</td>
|
||
|
|
</tr>
|
||
|
|
<tr>
|
||
|
|
<td style="vertical-align: top;">GL_STENCIL_BITS<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">1<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">Number of bits per stencil value
|
||
|
|
in the frame buffer.<br>
|
||
|
|
</td>
|
||
|
|
</tr>
|
||
|
|
<tr>
|
||
|
|
<td style="vertical-align: top;">GL_STENCIL_CLEAR_VALUE<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">1<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">Stencil buffer clear value.<br>
|
||
|
|
</td>
|
||
|
|
</tr>
|
||
|
|
<tr>
|
||
|
|
<td style="vertical-align: top;">GL_STENCIL_FAIL<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">1<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">Stencil fail operation.<br>
|
||
|
|
</td>
|
||
|
|
</tr>
|
||
|
|
<tr>
|
||
|
|
<td style="vertical-align: top;">GL_STENCIL_FUNC<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">1<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">Stencil function.<br>
|
||
|
|
</td>
|
||
|
|
</tr>
|
||
|
|
<tr>
|
||
|
|
<td style="vertical-align: top;">GL_STENCIL_REF<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">1<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">Stencil reference value.<br>
|
||
|
|
</td>
|
||
|
|
</tr>
|
||
|
|
<tr>
|
||
|
|
<td style="vertical-align: top;">GL_STENCIL_TEST<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">1<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">Zero if stencil test is disabled.<br>
|
||
|
|
One if stencil test is enabled.<br>
|
||
|
|
</td>
|
||
|
|
</tr>
|
||
|
|
<tr>
|
||
|
|
<td style="vertical-align: top;">GL_STENCIL_VALUE_MASK<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">1<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">Stencil mask value.<br>
|
||
|
|
</td>
|
||
|
|
</tr>
|
||
|
|
<tr>
|
||
|
|
<td style="vertical-align: top;">GL_STENCIL_WRITE_MASK<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">1<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">Stencil buffer write mask.<br>
|
||
|
|
</td>
|
||
|
|
</tr>
|
||
|
|
<tr>
|
||
|
|
<td style="vertical-align: top;">GL_TEXTURE_2D<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">1<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">Zero if 2D texture mapping is
|
||
|
|
disabled.<br>
|
||
|
|
One if 2D texture mapping is enabled.<br>
|
||
|
|
</td>
|
||
|
|
</tr>
|
||
|
|
<tr>
|
||
|
|
<td style="vertical-align: top;">GL_TEXTURE_BINDING_2D</td>
|
||
|
|
<td style="vertical-align: top;">1<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">Name of currently bound 2D
|
||
|
|
texture object.<br>
|
||
|
|
</td>
|
||
|
|
</tr>
|
||
|
|
<tr>
|
||
|
|
<td style="vertical-align: top;">GL_TEXTURE_ENV_COLOR<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">4<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">Texture environment color (red,
|
||
|
|
green, blue, alpha).<br>
|
||
|
|
</td>
|
||
|
|
</tr>
|
||
|
|
<tr>
|
||
|
|
<td style="vertical-align: top;">GL_TEXTURE_ENV_MODE<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">1<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">Texture environment mode.<br>
|
||
|
|
</td>
|
||
|
|
</tr>
|
||
|
|
<tr>
|
||
|
|
<td style="vertical-align: top;">GL_UNPACK_ROW_LENGTH<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">1<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">Pixel unpacking row length.<br>
|
||
|
|
</td>
|
||
|
|
</tr>
|
||
|
|
<tr>
|
||
|
|
<td style="vertical-align: top;">GL_UNPACK_LSB_FIRST<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">1<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">Zero if most significant bit is
|
||
|
|
unpacked first for bitmaps.<br>
|
||
|
|
One if least significant bit is unpacked first for bitmaps.<br>
|
||
|
|
</td>
|
||
|
|
</tr>
|
||
|
|
<tr>
|
||
|
|
<td style="vertical-align: top;">GL_VIEWPORT<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">4<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">Current viewport (x, y, width,
|
||
|
|
height).<br>
|
||
|
|
</td>
|
||
|
|
</tr>
|
||
|
|
</tbody>
|
||
|
|
</table>
|
||
|
|
<br>
|
||
|
|
<br>
|
||
|
|
<h2>9.2 String Queries</h2>
|
||
|
|
The command<br>
|
||
|
|
<br>
|
||
|
|
<div style="margin-left: 40px;">const GLubyte *<span
|
||
|
|
style="font-weight: bold;">glGetString</span>(GLenum <span
|
||
|
|
style="font-style: italic;">name</span>)<br>
|
||
|
|
</div>
|
||
|
|
<br>
|
||
|
|
is used to query string-valued values. The legal values for <span
|
||
|
|
style="font-style: italic;">name</span> are described in the following
|
||
|
|
table:<br>
|
||
|
|
<br>
|
||
|
|
<table cellpadding="2" cellspacing="2" border="1"
|
||
|
|
style="text-align: left; width: 80%; margin-left: auto; margin-right: auto;">
|
||
|
|
<tbody>
|
||
|
|
<tr>
|
||
|
|
<td style="vertical-align: top;"><span style="font-style: italic;">name</span><br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">Return value<br>
|
||
|
|
</td>
|
||
|
|
</tr>
|
||
|
|
<tr>
|
||
|
|
<td style="vertical-align: top;">GL_VERSION<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">The library version, such as
|
||
|
|
"1.2".<br>
|
||
|
|
</td>
|
||
|
|
</tr>
|
||
|
|
<tr>
|
||
|
|
<td style="vertical-align: top;">GL_RENDERER<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">The renderer, such as "Mesa DRI
|
||
|
|
Radeon".<br>
|
||
|
|
</td>
|
||
|
|
</tr>
|
||
|
|
<tr>
|
||
|
|
<td style="vertical-align: top;">GL_VENDOR<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">The vendor of this
|
||
|
|
implementation, such as "Tungsten Graphics, Inc."<br>
|
||
|
|
</td>
|
||
|
|
</tr>
|
||
|
|
<tr>
|
||
|
|
<td style="vertical-align: top;">GL_EXTENSIONS<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">A white-space separated list of
|
||
|
|
the supported extensions. </td>
|
||
|
|
</tr>
|
||
|
|
</tbody>
|
||
|
|
</table>
|
||
|
|
<br>
|
||
|
|
<h2>9.3 Error Queries</h2>
|
||
|
|
The command<br>
|
||
|
|
<br>
|
||
|
|
<div style="margin-left: 40px;">GLenum <span style="font-weight: bold;">glGetError</span>(void)<br>
|
||
|
|
</div>
|
||
|
|
<br>
|
||
|
|
returns the current error code. The current error code will be
|
||
|
|
set by a GL command when an error condition has been detected. If
|
||
|
|
the current error code is already set, subsequent errors will not be
|
||
|
|
recorded. The error code is reset/cleared to GL_NO_ERROR when <span
|
||
|
|
style="font-weight: bold;">glGetError</span> returns. The
|
||
|
|
following error codes are possible:<br>
|
||
|
|
<br>
|
||
|
|
<table cellpadding="2" cellspacing="2" border="1"
|
||
|
|
style="text-align: left; width: 80%; margin-left: auto; margin-right: auto;">
|
||
|
|
<tbody>
|
||
|
|
<tr>
|
||
|
|
<td style="vertical-align: top;">Error code<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">Meaning<br>
|
||
|
|
</td>
|
||
|
|
</tr>
|
||
|
|
<tr>
|
||
|
|
<td style="vertical-align: top;">GL_NO_ERROR<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">No error has been recorded.<br>
|
||
|
|
</td>
|
||
|
|
</tr>
|
||
|
|
<tr>
|
||
|
|
<td style="vertical-align: top;">GL_INVALID_ENUM<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">An enum parameter had an invalid
|
||
|
|
value.<br>
|
||
|
|
</td>
|
||
|
|
</tr>
|
||
|
|
<tr>
|
||
|
|
<td style="vertical-align: top;">GL_INVALID_VALUE<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">A numeric parameter had an
|
||
|
|
invalid value.<br>
|
||
|
|
</td>
|
||
|
|
</tr>
|
||
|
|
<tr>
|
||
|
|
<td style="vertical-align: top;">GL_INVALID_OPERATION<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">A function was called when not
|
||
|
|
legal to do so.<br>
|
||
|
|
</td>
|
||
|
|
</tr>
|
||
|
|
<tr>
|
||
|
|
<td style="vertical-align: top;">GL_STACK_OVERFLOW<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">The current transformation
|
||
|
|
matrix stack is full.<br>
|
||
|
|
</td>
|
||
|
|
</tr>
|
||
|
|
<tr>
|
||
|
|
<td style="vertical-align: top;">GL_STACK_UNDERFLOW<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">The current transformation
|
||
|
|
matrix stack is empty.<br>
|
||
|
|
</td>
|
||
|
|
</tr>
|
||
|
|
<tr>
|
||
|
|
<td style="vertical-align: top;">GL_OUT_OF_MEMORY<br>
|
||
|
|
</td>
|
||
|
|
<td style="vertical-align: top;">The system ran out of dynamic
|
||
|
|
memory.<br>
|
||
|
|
</td>
|
||
|
|
</tr>
|
||
|
|
</tbody>
|
||
|
|
</table>
|
||
|
|
<br>
|
||
|
|
<br>
|
||
|
|
<h1>10. Unsupported Features</h1>
|
||
|
|
This section lists other features and functions which are not supported
|
||
|
|
and not previously discussed.<br>
|
||
|
|
<br>
|
||
|
|
<h2>10.1 Feedback Mode</h2>
|
||
|
|
Feedback mode and the following related functions are not supported.<br>
|
||
|
|
<br>
|
||
|
|
<div style="margin-left: 40px;"><span style="font-weight: bold;">glFeedbackBuffer</span><br>
|
||
|
|
<span style="font-weight: bold;">glPassThrough</span><br>
|
||
|
|
</div>
|
||
|
|
<br>
|
||
|
|
<h2>10.2 1D and 3D Textures<br>
|
||
|
|
</h2>
|
||
|
|
Only 2D texture images are supported. The following functions
|
||
|
|
used to specify 1D and 3D texture images are not supported:<br>
|
||
|
|
<br>
|
||
|
|
<div style="margin-left: 40px;"><span style="font-weight: bold;">glTexImage1D</span><br
|
||
|
|
style="font-weight: bold;">
|
||
|
|
<span style="font-weight: bold;">glTexImage3D</span><br
|
||
|
|
style="font-weight: bold;">
|
||
|
|
<span style="font-weight: bold;">glTexSubImage1D</span><br
|
||
|
|
style="font-weight: bold;">
|
||
|
|
<span style="font-weight: bold;"> glTexSubImage3D</span><br
|
||
|
|
style="font-weight: bold;">
|
||
|
|
<span style="font-weight: bold;">glCopyTexImage1D</span><br
|
||
|
|
style="font-weight: bold;">
|
||
|
|
<span style="font-weight: bold;"> glCopyTexSubImage1D</span><br
|
||
|
|
style="font-weight: bold;">
|
||
|
|
<span style="font-weight: bold;"> glCopyTexSubImage3D</span><br>
|
||
|
|
</div>
|
||
|
|
<br>
|
||
|
|
<h2>10.3 Alternate Texture Image Commands<br>
|
||
|
|
</h2>
|
||
|
|
Texture images may only be specified with <span
|
||
|
|
style="font-weight: bold;">glTexImage2D</span>. The following
|
||
|
|
alternate texture image commands are not supported:<br>
|
||
|
|
<br>
|
||
|
|
<div style="margin-left: 40px; font-weight: bold;">glTexSubImage2D<br>
|
||
|
|
glCopyTexImage2D<br>
|
||
|
|
glCopyTexSubImage2D<br>
|
||
|
|
</div>
|
||
|
|
<br>
|
||
|
|
<h2>10.4 Proxy Textures</h2>
|
||
|
|
Proxy textures are not supported and the GL_PROXY_TEXTURE_2D token is
|
||
|
|
not supported by any function.<br>
|
||
|
|
<br>
|
||
|
|
<br>
|
||
|
|
<h2>10.5 Other Texture Commands</h2>
|
||
|
|
The following commands related to texture mapping are not supported by
|
||
|
|
the subset:<br>
|
||
|
|
<br>
|
||
|
|
<div style="margin-left: 40px; font-weight: bold;"> glPrioritizeTextures<br>
|
||
|
|
glAreTexturesResident<br>
|
||
|
|
glIsTexture<br>
|
||
|
|
glTexEnviv<br>
|
||
|
|
glTexEnvf<br>
|
||
|
|
glTexParameterf<br>
|
||
|
|
glTexParameteriv<br>
|
||
|
|
glTexParameterfv<br>
|
||
|
|
</div>
|
||
|
|
<br>
|
||
|
|
<br>
|
||
|
|
<h2>10.6 Copy and Draw Pixels<br>
|
||
|
|
</h2>
|
||
|
|
The following commands are not supported:<br>
|
||
|
|
<br>
|
||
|
|
<div style="margin-left: 40px;"><span style="font-weight: bold;">glDrawPixels<br>
|
||
|
|
glCopyPixels<br>
|
||
|
|
glPixelZoom<br>
|
||
|
|
<br>
|
||
|
|
</span></div>
|
||
|
|
<h2>10.7 Color Index Mode<br>
|
||
|
|
</h2>
|
||
|
|
Color index mode and the following related commands are not supported:<br>
|
||
|
|
<br>
|
||
|
|
<span style="font-weight: bold;"></span>
|
||
|
|
<div style="margin-left: 40px;"><span style="font-weight: bold;">glIndexub<br>
|
||
|
|
</span><span style="font-weight: bold;">glIndexi</span><br>
|
||
|
|
<span style="font-weight: bold;">glIndexs<br>
|
||
|
|
glIndexf<br>
|
||
|
|
glIndexd<br>
|
||
|
|
</span><span style="font-weight: bold;">glIndexubv<br>
|
||
|
|
</span><span style="font-weight: bold;">glIndexiv</span><br>
|
||
|
|
<span style="font-weight: bold;">glIndexsv<br>
|
||
|
|
glIndexfv<br>
|
||
|
|
glIndexdv</span><span style="font-weight: bold;"><br>
|
||
|
|
glIndexMask<br>
|
||
|
|
</span><span style="font-weight: bold;">glClearIndex<br>
|
||
|
|
glIndexPointer</span><br style="font-weight: bold;">
|
||
|
|
<br>
|
||
|
|
</div>
|
||
|
|
<h2>10.8 Pixel Transfer Operations</h2>
|
||
|
|
The pixel transfer operations (scale, bias, look-up table, etc) are not
|
||
|
|
supported and the following commands are omitted:<br>
|
||
|
|
<br style="font-weight: bold;">
|
||
|
|
<div style="margin-left: 40px;"><span style="font-weight: bold;">glPixelTransferf</span><br
|
||
|
|
style="font-weight: bold;">
|
||
|
|
<span style="font-weight: bold;">glPixelTransferi</span><br
|
||
|
|
style="font-weight: bold;">
|
||
|
|
<span style="font-weight: bold;">glPixelMapfv</span><br
|
||
|
|
style="font-weight: bold;">
|
||
|
|
<span style="font-weight: bold;">glPixelMapuiv</span><br
|
||
|
|
style="font-weight: bold;">
|
||
|
|
<span style="font-weight: bold;">glPixelMapusv</span><br
|
||
|
|
style="font-weight: bold;">
|
||
|
|
<span style="font-weight: bold;">glGetPixelMapfv</span><br
|
||
|
|
style="font-weight: bold;">
|
||
|
|
<span style="font-weight: bold;">glGetPixelMapuiv</span><br
|
||
|
|
style="font-weight: bold;">
|
||
|
|
<span style="font-weight: bold;">glGetPixelMapusv</span><br>
|
||
|
|
</div>
|
||
|
|
<br>
|
||
|
|
<h2>10.9 Hints</h2>
|
||
|
|
Hints and the following related command is not supported:<br>
|
||
|
|
<br>
|
||
|
|
<div style="margin-left: 40px;"><span style="font-weight: bold;">glHint<br>
|
||
|
|
</span><br>
|
||
|
|
</div>
|
||
|
|
<h2>10.10 State Query Commands<br>
|
||
|
|
</h2>
|
||
|
|
The following state query commands are not supported:<br>
|
||
|
|
<br>
|
||
|
|
<div style="margin-left: 40px; font-weight: bold;">glGetBooleanv<br>
|
||
|
|
glGetIntegerv<br>
|
||
|
|
glGetDoublev<br>
|
||
|
|
glGetPointerv<br>
|
||
|
|
glGetTexEnvi<br>
|
||
|
|
glGetTexEnvf<br>
|
||
|
|
glGetTexParameteriv<br>
|
||
|
|
glGetTexParameterfv<br>
|
||
|
|
glGetTexLevelParameteriv<br>
|
||
|
|
glGetTexLevelParameterfv<br>
|
||
|
|
glGetTexImage<br>
|
||
|
|
glGetClipPlane<br>
|
||
|
|
</div>
|
||
|
|
<br>
|
||
|
|
<h2>10.11 Attribute Stacks</h2>
|
||
|
|
State attribute stacks and the following related commands are not
|
||
|
|
supported:<br>
|
||
|
|
<br>
|
||
|
|
<div style="margin-left: 40px;"><span style="font-weight: bold;">glPushAttrib</span><br
|
||
|
|
style="font-weight: bold;">
|
||
|
|
<span style="font-weight: bold;">glPopAtttrib</span><br>
|
||
|
|
<br style="font-weight: bold;">
|
||
|
|
</div>
|
||
|
|
<h2>10.12 Double-Valued Functions</h2>
|
||
|
|
All functions which take double-precision floating point values, but
|
||
|
|
for which there is an equivalent single-precision valued function, are
|
||
|
|
omitted. This includes, but is not limited to:<br>
|
||
|
|
<br>
|
||
|
|
<div style="margin-left: 40px;"><span style="font-weight: bold;">glVertex2d</span><br
|
||
|
|
style="font-weight: bold;">
|
||
|
|
<span style="font-weight: bold;">glVertex2dv</span><br
|
||
|
|
style="font-weight: bold;">
|
||
|
|
<span style="font-weight: bold;">glVertex3d</span><br
|
||
|
|
style="font-weight: bold;">
|
||
|
|
<span style="font-weight: bold;"> glVertex3dv</span><br
|
||
|
|
style="font-weight: bold;">
|
||
|
|
<span style="font-weight: bold;">glVertex4d</span><br
|
||
|
|
style="font-weight: bold;">
|
||
|
|
<span style="font-weight: bold;"> glVertex4dv</span><br
|
||
|
|
style="font-weight: bold;">
|
||
|
|
<span style="font-weight: bold;">glColor3d</span><br
|
||
|
|
style="font-weight: bold;">
|
||
|
|
<span style="font-weight: bold;">glColor3d</span><span
|
||
|
|
style="font-weight: bold;">v</span><br style="font-weight: bold;">
|
||
|
|
<span style="font-weight: bold;">glColor4d</span><br
|
||
|
|
style="font-weight: bold;">
|
||
|
|
<span style="font-weight: bold;"> glColor4dv</span><br
|
||
|
|
style="font-weight: bold;">
|
||
|
|
<span style="font-weight: bold;">glTexCoord1d</span><br
|
||
|
|
style="font-weight: bold;">
|
||
|
|
<span style="font-weight: bold;">glTexCoord1d</span><span
|
||
|
|
style="font-weight: bold;">v</span><br style="font-weight: bold;">
|
||
|
|
<span style="font-weight: bold;">glTexCoord2d</span><br
|
||
|
|
style="font-weight: bold;">
|
||
|
|
<span style="font-weight: bold;"> glTexCoord2dv</span><br
|
||
|
|
style="font-weight: bold;">
|
||
|
|
<span style="font-weight: bold;">glTexCoord3d</span><br
|
||
|
|
style="font-weight: bold;">
|
||
|
|
<span style="font-weight: bold;"> glTexCoord3dv</span><br
|
||
|
|
style="font-weight: bold;">
|
||
|
|
<span style="font-weight: bold;">glTexCoord4d</span><br
|
||
|
|
style="font-weight: bold;">
|
||
|
|
<span style="font-weight: bold;"> glTexCoord4dv</span><br
|
||
|
|
style="font-weight: bold;">
|
||
|
|
<span style="font-weight: bold;">glRasterPos2d</span><br
|
||
|
|
style="font-weight: bold;">
|
||
|
|
<span style="font-weight: bold;"> glRasterPos2dv</span><br
|
||
|
|
style="font-weight: bold;">
|
||
|
|
<span style="font-weight: bold;">glRasterPos3d</span><br
|
||
|
|
style="font-weight: bold;">
|
||
|
|
<span style="font-weight: bold;"> glRasterPos3dv</span><br
|
||
|
|
style="font-weight: bold;">
|
||
|
|
<span style="font-weight: bold;">glRasterPos4d</span><br
|
||
|
|
style="font-weight: bold;">
|
||
|
|
<span style="font-weight: bold;"> glRasterPos4dv</span><br
|
||
|
|
style="font-weight: bold;">
|
||
|
|
<span style="font-weight: bold;">glLoadMatrixd</span><br
|
||
|
|
style="font-weight: bold;">
|
||
|
|
<span style="font-weight: bold;">glMultMatrixd</span><br
|
||
|
|
style="font-weight: bold;">
|
||
|
|
<span style="font-weight: bold;">glScaled</span><br
|
||
|
|
style="font-weight: bold;">
|
||
|
|
<span style="font-weight: bold;">glRotated</span><br
|
||
|
|
style="font-weight: bold;">
|
||
|
|
<span style="font-weight: bold;">glTranslated<br>
|
||
|
|
glRectd<br>
|
||
|
|
glRectdv<br>
|
||
|
|
</span> <span style="font-weight: bold;"><br>
|
||
|
|
</span> </div>
|
||
|
|
<h2>10.13 Evaluators</h2>
|
||
|
|
Evaluators and the following related commands are not supported:<br>
|
||
|
|
<br>
|
||
|
|
<div style="margin-left: 40px;"><span style="font-weight: bold;">glMap1f</span><br
|
||
|
|
style="font-weight: bold;">
|
||
|
|
<span style="font-weight: bold;">glMap2d</span><br
|
||
|
|
style="font-weight: bold;">
|
||
|
|
<span style="font-weight: bold;">glMap2f</span><br
|
||
|
|
style="font-weight: bold;">
|
||
|
|
<span style="font-weight: bold;">glGetMapdv</span><br
|
||
|
|
style="font-weight: bold;">
|
||
|
|
<span style="font-weight: bold;">glGetMapfv</span><br
|
||
|
|
style="font-weight: bold;">
|
||
|
|
<span style="font-weight: bold;">glGetMapiv</span><br
|
||
|
|
style="font-weight: bold;">
|
||
|
|
<span style="font-weight: bold;">glEvalCoord1d</span><br
|
||
|
|
style="font-weight: bold;">
|
||
|
|
<span style="font-weight: bold;">glEvalCoord1f</span><br
|
||
|
|
style="font-weight: bold;">
|
||
|
|
<span style="font-weight: bold;">glEvalCoord1dv</span><br
|
||
|
|
style="font-weight: bold;">
|
||
|
|
<span style="font-weight: bold;">glEvalCoord1fv</span><br
|
||
|
|
style="font-weight: bold;">
|
||
|
|
<span style="font-weight: bold;">glEvalCoord2d</span><br
|
||
|
|
style="font-weight: bold;">
|
||
|
|
<span style="font-weight: bold;">glEvalCoord2f</span><br
|
||
|
|
style="font-weight: bold;">
|
||
|
|
<span style="font-weight: bold;">glEvalCoord2dv</span><br
|
||
|
|
style="font-weight: bold;">
|
||
|
|
<span style="font-weight: bold;">glEvalCoord2fv</span><br
|
||
|
|
style="font-weight: bold;">
|
||
|
|
<span style="font-weight: bold;">glMapGrid1d</span><br
|
||
|
|
style="font-weight: bold;">
|
||
|
|
<span style="font-weight: bold;">glMapGrid1f</span><br
|
||
|
|
style="font-weight: bold;">
|
||
|
|
<span style="font-weight: bold;">glMapGrid2d</span><br
|
||
|
|
style="font-weight: bold;">
|
||
|
|
<span style="font-weight: bold;">glMapGrid2f</span><br
|
||
|
|
style="font-weight: bold;">
|
||
|
|
<span style="font-weight: bold;">glEvalPoint1</span><br
|
||
|
|
style="font-weight: bold;">
|
||
|
|
<span style="font-weight: bold;">glEvalPoint2</span><br
|
||
|
|
style="font-weight: bold;">
|
||
|
|
<span style="font-weight: bold;">glEvalMesh1</span><br
|
||
|
|
style="font-weight: bold;">
|
||
|
|
<span style="font-weight: bold;">glEvalMesh2</span><br
|
||
|
|
style="font-weight: bold;">
|
||
|
|
</div>
|
||
|
|
<br>
|
||
|
|
<h2>10.14 Display Lists</h2>
|
||
|
|
Display lists and the following related commands are not supported:<br>
|
||
|
|
<br>
|
||
|
|
<div style="margin-left: 40px; font-weight: bold;">glIsList<br>
|
||
|
|
glDeleteLists<br>
|
||
|
|
glGenLists<br>
|
||
|
|
glNewList<br>
|
||
|
|
glEndList<br>
|
||
|
|
glCallList<br>
|
||
|
|
glCallLists<br>
|
||
|
|
glListBase<br>
|
||
|
|
</div>
|
||
|
|
<br>
|
||
|
|
<h2>10.15 Accumulation Buffer</h2>
|
||
|
|
The accumulation buffer and the following related commands are not
|
||
|
|
supported:<br>
|
||
|
|
<br style="font-weight: bold;">
|
||
|
|
<div style="margin-left: 40px;"><span style="font-weight: bold;">glAccum</span><br
|
||
|
|
style="font-weight: bold;">
|
||
|
|
<span style="font-weight: bold;">glClearAccum</span><br>
|
||
|
|
</div>
|
||
|
|
<br>
|
||
|
|
<h2>10.16 Fog</h2>
|
||
|
|
Fog and the following related commands are not supported:<br>
|
||
|
|
<br>
|
||
|
|
<div style="margin-left: 40px; font-weight: bold;"> glFogi<br>
|
||
|
|
glFogf<br>
|
||
|
|
glFogiv<br>
|
||
|
|
glFogfv<br>
|
||
|
|
</div>
|
||
|
|
<br>
|
||
|
|
<h2>10.17 Depth Test</h2>
|
||
|
|
Depth testing and the following related commands are not supported:<br>
|
||
|
|
<br>
|
||
|
|
<div style="margin-left: 40px;"><span style="font-weight: bold;">glDepthFunc</span><br
|
||
|
|
style="font-weight: bold;">
|
||
|
|
<span style="font-weight: bold;">glDepthMask</span><br
|
||
|
|
style="font-weight: bold;">
|
||
|
|
<span style="font-weight: bold;">glDepthRange</span><br
|
||
|
|
style="font-weight: bold;">
|
||
|
|
<span style="font-weight: bold;">glClearDepth</span><br>
|
||
|
|
</div>
|
||
|
|
<br>
|
||
|
|
<h2>10.18 Imaging Subset</h2>
|
||
|
|
The OpenGL imaging subset (which implements features such as
|
||
|
|
convolution, histogram, min/max recording, color matrix and color
|
||
|
|
tables) is not supported.<br>
|
||
|
|
<br>
|
||
|
|
<br>
|
||
|
|
<h1>Appendix A: Issues</h1>
|
||
|
|
This appendix lists documentation and subset issues with their current
|
||
|
|
status. For items which are still open, the documentation (above)
|
||
|
|
follows the recommended solution.<br>
|
||
|
|
<br>
|
||
|
|
<h2>A.1 Vertex Arrays</h2>
|
||
|
|
Should vertex arrays be supported? Is there a performance
|
||
|
|
advantage?<br>
|
||
|
|
<br>
|
||
|
|
RESOLUTION: No, there isn't enough of a performance advantage to
|
||
|
|
justify them.<br>
|
||
|
|
<br>
|
||
|
|
<h2>A.2 Polygon Antialiasing and Edge Flags</h2>
|
||
|
|
Should edge flags be supported for antialiasing?<br>
|
||
|
|
<br>
|
||
|
|
Edge flags don't effect antialiasing, at least not normally. A
|
||
|
|
number of approaches to antialiasing have been summarized in email.<br>
|
||
|
|
<br>
|
||
|
|
RECOMMENDATION: don't support edge flags. They don't effect
|
||
|
|
polygon antialiasing.<br>
|
||
|
|
<br>
|
||
|
|
RESOLUTION: closed, as of 26 Feb 2003.<br>
|
||
|
|
<br>
|
||
|
|
<h2>A.3 glRasterPos vs. glWindowPos</h2>
|
||
|
|
Should glRasterPos and/or glWindowPos commands be supported?<br>
|
||
|
|
<br>
|
||
|
|
RESOLUTION: Closed: implement glRasterPos commands, but not glWindowPos
|
||
|
|
commands.<br>
|
||
|
|
<br>
|
||
|
|
<h2>A.4 GL_IBM_rasterpos_clip extension</h2>
|
||
|
|
Should the GL_IBM_rasterpos_clip extension be implemented?<br>
|
||
|
|
<br>
|
||
|
|
RESOLUTION: No. It's not required.<br>
|
||
|
|
<br>
|
||
|
|
<h2>A.5 Image Formats and Types</h2>
|
||
|
|
Which image formats and types should be supported for <span
|
||
|
|
style="font-weight: bold;">glTexImage2D</span> and <span
|
||
|
|
style="font-weight: bold;">glReadPixels</span>?<br>
|
||
|
|
<br>
|
||
|
|
OpenGL specifies a <span style="font-weight: bold;">large</span>
|
||
|
|
variety of image formats and data types. Only a few are commonly
|
||
|
|
used.<br>
|
||
|
|
<br>
|
||
|
|
RECOMMENDATION: we propose a subset:<br>
|
||
|
|
<br>
|
||
|
|
For <span style="font-weight: bold;">glTexImage2D</span> only allow <span
|
||
|
|
style="font-style: italic;">type</span>=GL_UNSIGNED_BYTE and <span
|
||
|
|
style="font-style: italic;">format</span>=GL_RGBA, GL_RGB,
|
||
|
|
GL_INTENSITY. Only allow <span style="font-style: italic;">internalFormat</span>
|
||
|
|
to be GL_RGBA, GL_RGB or GL_INTENSITY as well. Basically, only
|
||
|
|
support image formats/types that are directly supported by the Radeon
|
||
|
|
hardware. This will allow <span style="font-weight: bold;">glTexImage2D</span>
|
||
|
|
to basically just use <span style="font-weight: bold;">memcpy</span> to
|
||
|
|
copy texture images.<br>
|
||
|
|
<br>
|
||
|
|
For <span style="font-weight: bold;">glReadPixels</span>, only allow <span
|
||
|
|
style="font-style: italic;">type</span> = GL_UNSIGNED_BYTE or GL_FLOAT.
|
||
|
|
Only allow <span style="font-style: italic;">format</span> =
|
||
|
|
GL_RGB or GL_RGBA. This is just enough to support the OpenGL
|
||
|
|
conformance tests.<br>
|
||
|
|
<br>
|
||
|
|
RESOLUTION: open<br>
|
||
|
|
<br>
|
||
|
|
<h2>A.6 Texture Environment Modes</h2>
|
||
|
|
Which texture environment modes should be supported? OpenGL 1.2
|
||
|
|
has GL_REPLACE, GL_MODULATE, GL_DECAL and GL_BLEND. GL_DECAL isn't
|
||
|
|
defined for all base internal texture formats. GL_ADD is another
|
||
|
|
useful mode. Perhaps drop GL_DECAL mode and add GL_ADD mode.<br>
|
||
|
|
<br>
|
||
|
|
RECOMMENDATION: implement the standard modes GL_REPLACE, GL_MODULATE,
|
||
|
|
GL_DECAL and GL_BLEND.<br>
|
||
|
|
<br>
|
||
|
|
RESOLUTION: open<br>
|
||
|
|
<br>
|
||
|
|
<h2>A.7 Truncated Mipmaps and LOD Control</h2>
|
||
|
|
Should we support the GL_TEXTURE_BASE_LEVEL, GL_TEXTURE_MAX_LEVEL,
|
||
|
|
GL_TEXTURE_MIN_LOD and GL_TEXTURE_MAX_LOD texture parameters?<br>
|
||
|
|
<br>
|
||
|
|
RECOMMENDATION: We propose omitting these features at this time,
|
||
|
|
in the interest of simplifying the driver.<br>
|
||
|
|
<br>
|
||
|
|
RESOLUTION: open<br>
|
||
|
|
<br>
|
||
|
|
<h2>A.8 Texture Priorities and Residency</h2>
|
||
|
|
Should the subset support texture priorities via <span
|
||
|
|
style="font-weight: bold;">glPrioritizeTextures</span> and the <span
|
||
|
|
style="font-weight: bold;">glAreTexturesResident</span> command?<br>
|
||
|
|
<br>
|
||
|
|
RECOMMENDATION: Few applications use these features and
|
||
|
|
functions. We propose omitting them to simplify the driver.<br>
|
||
|
|
<br>
|
||
|
|
RESOLUTION: open<br>
|
||
|
|
<br>
|
||
|
|
<h2>A.9 Pixel Pack/Unpack Alignment Control</h2>
|
||
|
|
Should we support the GL_PACK_ALIGNMENT and GL_UNPACK_ALIGNMENT options?<br>
|
||
|
|
<br>
|
||
|
|
These are used to align pixel data addresses to 1, 2 and 4-byte
|
||
|
|
multiples for <span style="font-weight: bold;">glBitmap, glTexImage2D</span>
|
||
|
|
and <span style="font-weight: bold;">glReadPixels</span>. These
|
||
|
|
aren't strictly needed since the user can provide a 1, 2 or 4-byte
|
||
|
|
aligned address and appropriate GL_PACK_ROW_LENGTH or
|
||
|
|
GL_UNPACK_ROW_LENGTH values instead.<br>
|
||
|
|
<br>
|
||
|
|
RECOMMENDATION: We recommend omitting them to simplify the driver.<br>
|
||
|
|
<br>
|
||
|
|
RESOLUTION: open<br>
|
||
|
|
<br>
|
||
|
|
<h2>A.10 Pixel Pack/Unpack Skip Rows/Pixels Control</h2>
|
||
|
|
Should we support the GL_UNPACK_SKIP_PIXELS, GL_UNPACK_SKIP_ROWS,
|
||
|
|
GL_PACK_SKIP_PIXELS and GL_PACK_SKIP_ROWS options for pixel
|
||
|
|
unpacking/packing?<br>
|
||
|
|
<br>
|
||
|
|
These options aren't really needed since the user can adjust the start
|
||
|
|
address and GL_PACK/UNPACK_ROW_LENGTH parameters to achieve the same
|
||
|
|
effect.<br>
|
||
|
|
<br>
|
||
|
|
RECOMMENDATION: omit these parameters.<br>
|
||
|
|
<br>
|
||
|
|
RESOLUTION: open<br>
|
||
|
|
<br>
|
||
|
|
<h2>A.11 Texture State Queries</h2>
|
||
|
|
Should we support the command <span style="font-weight: bold;">glGetTexEnvi/fv,
|
||
|
|
glGetTexParameteri/fv</span> and <span style="font-weight: bold;">glGetTexLevelParameteri/fv</span>?<br>
|
||
|
|
<br>
|
||
|
|
RECOMMENDATION: No. They're seldom needed and their
|
||
|
|
implementation is several hundred lines of code in length.<br>
|
||
|
|
<br>
|
||
|
|
RESOLUTION: open<br>
|
||
|
|
<br>
|
||
|
|
<h2>A.12 glGetIntegerv, glGetBooleanv and glGetDoublev</h2>
|
||
|
|
Should we support the commands <span style="font-weight: bold;">glGetIntegerv,
|
||
|
|
glGetBooleanv </span>and <span style="font-weight: bold;">glGetDoublev</span>
|
||
|
|
in addition to <span style="font-weight: bold;">glGetFloatv</span>?<br>
|
||
|
|
<br>
|
||
|
|
RECOMMENDATION: Omit the boolean, integer and double-valued
|
||
|
|
functions. All state values which can be queried by these commands can
|
||
|
|
be expressed as floating point values and queried with <span
|
||
|
|
style="font-weight: bold;">glGetFloatv</span>. The
|
||
|
|
implementation of the other three commands involves many lines of code.<br>
|
||
|
|
<br>
|
||
|
|
RESOLUTION: open<br>
|
||
|
|
<br>
|
||
|
|
<h2>A.13 glBitmap and Per-Fragment Operations</h2>
|
||
|
|
Should bitmaps rendered with <span style="font-weight: bold;">glBitmap</span>
|
||
|
|
be subjected to the per-fragment operations?<br>
|
||
|
|
<br>
|
||
|
|
If bitmaps are implemented with points it will be easy to implement the
|
||
|
|
per-fragment operations. Otherwise, it could be difficult.<br>
|
||
|
|
<br>
|
||
|
|
RECOMMENDATION: Implement glBitmap by drawing points/pixels with
|
||
|
|
the hardware. This will make supporting the per-fragments
|
||
|
|
trivially easy. Also, it makes portrait-mode display relatively
|
||
|
|
easy.<br>
|
||
|
|
<br>
|
||
|
|
RESOLUTION: open<br>
|
||
|
|
<br>
|
||
|
|
<h2>A.14 Reduced gl.h Header File</h2>
|
||
|
|
Should we produce a reduced gl.h header file which only defines the
|
||
|
|
tokens and functions which are implemented by the subset?<br>
|
||
|
|
<br>
|
||
|
|
RECOMMENDATION: yes. It would be a useful reference to
|
||
|
|
programmers to quickly determine which functions and tokens are
|
||
|
|
supported.<br>
|
||
|
|
<br>
|
||
|
|
RESOLUTION: open<br>
|
||
|
|
<br>
|
||
|
|
<h2>A.15 glPolygonMode</h2>
|
||
|
|
Is <span style="font-weight: bold;">glPolygonMode</span> needed?<br>
|
||
|
|
<br>
|
||
|
|
RECOMMENDATION: No. Omit it.<br>
|
||
|
|
<br>
|
||
|
|
RESOLUTION: closed, as of 26 Feb 2003<br>
|
||
|
|
<br>
|
||
|
|
<br>
|
||
|
|
<p> </p>
|
||
|
|
</body>
|
||
|
|
</html>
|