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402 lines
13 KiB
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<head><title>Mesa FAQ</title></head>
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<link rel="stylesheet" type="text/css" href="mesa.css"></head>
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<BODY>
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<center>
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<h1>Mesa Frequently Asked Questions</h1>
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Last updated: 21 August 2006
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</center>
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<br>
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<br>
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<h2>Index</h2>
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<a href="#part1">1. High-level Questions and Answers</a>
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<br>
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<a href="#part2">2. Compilation and Installation Problems</a>
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<br>
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<a href="#part3">3. Runtime / Rendering Problems</a>
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<br>
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<a href="#part4">4. Developer Questions</a>
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<br>
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<br>
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<br>
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<a name="part1">
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</a><h1><a name="part1">1. High-level Questions and Answers</a></h1>
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<h2><a name="part1">1.1 What is Mesa?</a></h2>
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<p>
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<a name="part1">Mesa is an open-source implementation of the OpenGL specification.
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OpenGL is a programming library for writing interactive 3D applications.
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See the </a><a href="http://www.opengl.org/">OpenGL website</a> for more
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information.
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</p>
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<p>
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Mesa 6.x supports the OpenGL 1.5 specification.
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</p>
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<h2>1.2 Does Mesa support/use graphics hardware?</h2>
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<p>
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Yes. Specifically, Mesa serves as the OpenGL core for the open-source DRI
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drivers for XFree86/X.org. See the <a href="http://dri.freedesktop.org/">DRI
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website</a> for more information.
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</p>
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<p>
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There have been other hardware drivers for Mesa over the years (such as
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the 3Dfx Glide/Voodoo driver, an old S3 driver, etc) but the DRI drivers
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are the modern ones.
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</p>
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<h2>1.3 What purpose does Mesa serve today?</h2>
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<p>
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Hardware-accelerated OpenGL implementations are available for most popular
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operating systems today.
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Still, Mesa serves at least these purposes:
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</p>
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<ul>
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<li>Mesa is used as the core of the open-source XFree86/X.org DRI
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hardware drivers.
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</li>
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<li>Mesa is quite portable and allows OpenGL to be used on systems
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that have no other OpenGL solution.
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</li>
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<li>Software rendering with Mesa serves as a reference for validating the
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hardware drivers.
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</li>
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<li>A software implementation of OpenGL is useful for experimentation,
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such as testing new rendering techniques.
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</li>
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<li>Mesa can render images with deep color channels: 16-bit integer
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and 32-bit floating point color channels are supported.
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This capability is only now appearing in hardware.
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</li>
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<li>Mesa's internal limits (max lights, clip planes, texture size, etc) can be
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changed for special needs (hardware limits are hard to overcome).
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</li>
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</ul>
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<h2>1.4 What's the difference between"Stand-Alone" Mesa and the DRI drivers?</h2>
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<p>
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<em>Stand-alone Mesa</em> is the original incarnation of Mesa.
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On systems running the X Window System it does all its rendering through
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the Xlib API:
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<ul>
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<li>The GLX API is supported, but it's really just an emulation of the
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real thing.
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<li>The GLX wire protocol is not supported and there's no OpenGL extension
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loaded by the X server.
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<li>There is no hardware acceleration.
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<li>The OpenGL library, libGL.so, contains everything (the programming API,
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the GLX functions and all the rendering code).
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</ul>
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</p>
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<p>
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Alternately, Mesa acts as the core for a number of OpenGL hardware drivers
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within the DRI (Direct Rendering Infrastructure):
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<ul>
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<li>The libGL.so library provides the GL and GLX API functions, a GLX
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protocol encoder, and a device driver loader.
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<li>The device driver modules (such as r200_dri.so) contain a built-in
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copy of the core Mesa code.
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<li>The X server loads the GLX module.
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The GLX module decodes incoming GLX protocol and dispatches the commands
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to a rendering module.
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For the DRI, this module is basically a software Mesa renderer.
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</ul>
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<h2>1.5 How do I upgrade my DRI installation to use a new Mesa release?</h2>
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<p>
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This wasn't easy in the past.
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Now, the DRI drivers are included in the Mesa tree and can be compiled
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separately from the X server.
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Just follow the Mesa <a href="install.html">compilation instructions</a>.
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</p>
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<h2>1.6 Are there other open-source implementations of OpenGL?</h2>
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<p>
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Yes, SGI's <a href="http://oss.sgi.com/projects/ogl-sample/index.html"
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target="_parent">
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OpenGL Sample Implemenation (SI)</a> is available.
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The SI was written during the time that OpenGL was originally designed.
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Unfortunately, development of the SI has stagnated.
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Mesa is much more up to date with modern features and extensions.
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</p>
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<p>
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<a href="http://ogl-es.sourceforge.net" target="_parent">Vincent</a> is
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an open-source implementation of OpenGL ES for mobile devices.
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<p>
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<a href="http://www.dsbox.com/minigl.html" target="_parent">miniGL</a>
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is a subset of OpenGL for PalmOS devices.
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<p>
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<a href="http://fabrice.bellard.free.fr/TinyGL/"
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target="_parent">TinyGL</a> is a subset of OpenGL.
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</p>
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<p>
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<a href="http://softgl.studierstube.org/" target="_parent">SoftGL</a>
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is an OpenGL subset for mobile devices.
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</p>
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<p>
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<a href="http://chromium.sourceforge.net/" target="_parent">Chromium</a>
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isn't a conventional OpenGL implementation (it's layered upon OpenGL),
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but it does export the OpenGL API. It allows tiled rendering, sort-last
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rendering, etc.
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</p>
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<p>
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<a href="http://www.ticalc.org/archives/files/fileinfo/361/36173.html"
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target="_parent">ClosedGL</a> is an OpenGL subset library for TI
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graphing calculators.
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</p>
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<p>
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There may be other open OpenGL implementations, but Mesa is the most
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popular and feature-complete.
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</p>
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<br>
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<br>
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<a name="part2">
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</a><h1><a name="part2">2. Compilation and Installation Problems</a></h1>
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<h2><a name="part2">2.1 What's the easiest way to install Mesa?</a></h2>
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<p>
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<a name="part2">If you're using a Linux-based system, your distro CD most likely already
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has Mesa packages (like RPM or DEB) which you can easily install.
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</a></p>
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<h2><a name="part2">2.2 Running <code>configure; make</code> doesn't Work</a></h2>
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<p>
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Mesa no longer supports GNU autoconf/automake. Why?
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<ul>
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<li>It seemed to seldom work on anything but Linux
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<li>The config files were hard to maintain and hard to understand
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<li>libtool caused a lot of grief
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</ul>
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<p>
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Now Mesa again uses a conventional Makefile system (as it did originally).
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Basically, each Makefile in the tree includes one of the configuration
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files from the config/ directory.
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The config files specify all the variables for a variety of popular systems.
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</p>
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<h2><a name="part2">2.3 I get undefined symbols such as bgnpolygon, v3f, etc...</a></h2>
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<p>
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<a name="part2">You're application is written in IRIS GL, not OpenGL.
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IRIS GL was the predecessor to OpenGL and is a different thing (almost)
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entirely.
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Mesa's not the solution.
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</a></p>
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<h2><a name="part2">2.4 Where is the GLUT library?</a></h2>
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<p>
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<a name="part2">GLUT (OpenGL Utility Toolkit) is in the separate MesaGLUT-x.y.z.tar.gz file.
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If you don't already have GLUT installed, you should grab the MesaGLUT
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package and compile it with the rest of Mesa.
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</a></p>
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<h2><a name="part2">2.5 What's the proper place for the libraries and headers?</a></h2>
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<p>
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<a name="part2">On Linux-based systems you'll want to follow the
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</a><a href="http://oss.sgi.com/projects/ogl-sample/ABI/index.html"
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target="_parent">Linux ABI</a> standard.
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Basically you'll want the following:
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</p>
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<ul>
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<li>/usr/include/GL/gl.h - the main OpenGL header
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</li><li>/usr/include/GL/glu.h - the OpenGL GLU (utility) header
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</li><li>/usr/include/GL/glx.h - the OpenGL GLX header
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</li><li>/usr/include/GL/glext.h - the OpenGL extensions header
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</li><li>/usr/include/GL/glxext.h - the OpenGL GLX extensions header
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</li><li>/usr/include/GL/osmesa.h - the Mesa off-screen rendering header
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</li><li>/usr/lib/libGL.so - a symlink to libGL.so.1
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</li><li>/usr/lib/libGL.so.1 - a symlink to libGL.so.1.xyz
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</li><li>/usr/lib/libGL.so.xyz - the actual OpenGL/Mesa library. xyz denotes the
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Mesa version number.
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</li><li>/usr/lib/libGLU.so - a symlink to libGLU.so.1
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</li><li>/usr/lib/libGLU.so.1 - a symlink to libGLU.so.1.3.xyz
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</li><li>/usr/lib/libGLU.so.xyz - the OpenGL Utility library. xyz denotes the Mesa
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version number.
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</li></ul>
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<p>
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After installing XFree86/X.org and the DRI drivers, some of these files
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may be symlinks into the /usr/X11R6/ tree.
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</p>
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<p>
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The old-style Makefile system doesn't install the Mesa libraries; it's
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up to you to copy them (and the headers) to the right place.
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</p>
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<p>
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The GLUT header and library should go in the same directories.
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</p>
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<br>
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<br>
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<a name="part3">
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</a><h1><a name="part3">3. Runtime / Rendering Problems</a></h1>
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<h2><a name="part3">3.1 Rendering is slow / why isn't my graphics hardware being used?</a></h2>
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<p>
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<a name="part3">Stand-alone Mesa (downloaded as MesaLib-x.y.z.tar.gz) doesn't have any
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support for hardware acceleration (with the exception of the 3DFX Voodoo
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driver).
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</a></p>
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<p>
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<a name="part3">What you really want is a DRI or NVIDIA (or another vendor's OpenGL) driver
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for your particular hardware.
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</a></p>
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<p>
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<a name="part3">You can run the <code>glxinfo</code> program to learn about your OpenGL
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library.
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Look for the GL_VENDOR and GL_RENDERER values.
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That will identify who's OpenGL library you're using and what sort of
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hardware it has detected.
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</a></p>
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<p>
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<a name="part3">If your DRI-based driver isn't working, go to the
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</a><a href="http://dri.sf.net/" target="_parent">DRI website</a> for trouble-shooting information.
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</p>
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<h2>3.2 I'm seeing errors in depth (Z) buffering. Why?</h2>
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<p>
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Make sure the ratio of the far to near clipping planes isn't too great.
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Look
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<a href="http://www.opengl.org/resources/faq/technical/depthbuffer.htm#0040"
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target="_parent"> here</a> for details.
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</p>
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<p>
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Mesa uses a 16-bit depth buffer by default which is smaller and faster
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to clear than a 32-bit buffer but not as accurate.
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If you need a deeper you can modify the parameters to
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<code> glXChooseVisual</code> in your code.
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</p>
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<h2>3.3 Why Isn't depth buffering working at all?</h2>
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<p>
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Be sure you're requesting a depth buffered-visual. If you set the MESA_DEBUG
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environment variable it will warn you about trying to enable depth testing
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when you don't have a depth buffer.
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</p>
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<p>Specifically, make sure <code>glutInitDisplayMode</code> is being called
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with <code>GLUT_DEPTH</code> or <code>glXChooseVisual</code> is being
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called with a non-zero value for GLX_DEPTH_SIZE.
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</p>
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<p>This discussion applies to stencil buffers, accumulation buffers and
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alpha channels too.
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</p>
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<h2>3.4 Why does glGetString() always return NULL?</h2>
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<p>
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Be sure you have an active/current OpenGL rendering context before
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calling glGetString.
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</p>
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<h2>3.5 GL_POINTS and GL_LINES don't touch the right pixels</h2>
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<p>
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If you're trying to draw a filled region by using GL_POINTS or GL_LINES
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and seeing holes or gaps it's because of a float-to-int rounding problem.
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But this is not a bug.
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See Appendix H of the OpenGL Programming Guide - "OpenGL Correctness Tips".
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Basically, applying a translation of (0.375, 0.375, 0.0) to your coordinates
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will fix the problem.
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</p>
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<br>
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<br>
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<a name="part4">
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</a><h1><a name="part4">4. Developer Questions</a></h1>
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<h2>4.1 How can I contribute?</a></h2>
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<p>
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First, join the <a href="http://www.mesa3d.org/lists.html>Mesa3d-dev
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mailing list</a>.
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That's where Mesa development is discussed.
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</a></p>
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<p>
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The </a><a href="http://www.opengl.org/documentation" target="_parent">
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OpenGL Specification</a> is the bible for OpenGL implemention work.
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You should read it.
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</p>
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<p>Most of the Mesa development work involves implementing new OpenGL
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extensions, writing hardware drivers (for the DRI), and code optimization.
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</p>
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<h2>4.2 How do I write a new device driver?</h2>
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<p>
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Unfortunately, writing a device driver isn't easy.
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It requires detailed understanding of OpenGL, the Mesa code, and your
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target hardware/operating system.
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3D graphics are not simple.
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</p>
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<p>
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The best way to get started is to use an existing driver as your starting
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point.
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For a software driver, the X11 and OSMesa drivers are good examples.
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For a hardware driver, the Radeon and R200 DRI drivers are good examples.
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</p>
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<p>The DRI website has more information about writing hardware drivers.
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The process isn't well document because the Mesa driver interface changes
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over time, and we seldome have spare time for writing documentation.
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That being said, many people have managed to figure out the process.
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</p>
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<p>
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Joining the appropriate mailing lists and asking questions (and searching
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the archives) is a good way to get information.
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</p>
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<h2>4.3 Why isn't GL_EXT_texture_compression_s3tc implemented in Mesa?</h2>
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<p>
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The <a href="http://oss.sgi.com/projects/ogl-sample/registry/EXT/texture_compression_s3tc.txt" target="_parent">specification for the extension</a>
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indicates that there are intellectual property (IP) and/or patent issues
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to be dealt with.
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</p>
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<p>We've been unsucessful in getting a response from S3 (or whoever owns
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the IP nowadays) to indicate whether or not an open source project can
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implement the extension (specifically the compression/decompression
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algorithms).
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</p>
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<p>
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In the mean time, a 3rd party <a href=
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"http://homepage.hispeed.ch/rscheidegger/dri_experimental/s3tc_index.html"
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target="_parent">plug-in library</a> is available.
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</p>
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</body>
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</html>
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