261 lines
5.7 KiB
C
261 lines
5.7 KiB
C
/**
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* Implement smooth (AA) points with shaders.
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* A simple variation could be used for sprite points.
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* Brian Paul
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* 29 July 2007
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*/
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#include <assert.h>
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#include <string.h>
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#include <stdio.h>
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#include <stdlib.h>
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#include <math.h>
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#include <GL/gl.h>
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#include <GL/glut.h>
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#include <GL/glext.h>
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#include "extfuncs.h"
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#include "shaderutil.h"
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static GLuint FragShader;
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static GLuint VertShader;
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static GLuint Program;
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static GLint Win = 0;
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static GLint WinWidth = 500, WinHeight = 200;
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static GLfloat Xpos = 0.0f, Ypos = 0.0f;
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static GLint uViewportInv;
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static GLboolean Smooth = GL_TRUE, Blend = GL_TRUE;
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/**
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* Issue vertices for a "shader point".
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* The position is duplicated, only texcoords (or other vertex attrib) change.
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* The vertex program will compute the "real" quad corners.
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*/
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static void
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PointVertex3f(GLfloat x, GLfloat y, GLfloat z)
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{
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glTexCoord2f(-1, -1);
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glVertex3f(x, y, z);
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glTexCoord2f( 1, -1);
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glVertex3f(x, y, z);
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glTexCoord2f( 1, 1);
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glVertex3f(x, y, z);
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glTexCoord2f(-1, 1);
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glVertex3f(x, y, z);
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}
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static void
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DrawPoints(GLboolean shaderPoints)
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{
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int i;
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for (i = 0; i < 9; i++) {
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GLfloat x = i - 4, y = 0, z = 0;
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/* note: can't call glPointSize inside Begin/End :( */
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glPointSize( 2 + i * 5 );
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if (shaderPoints) {
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glBegin(GL_QUADS);
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PointVertex3f(x, y, z);
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glEnd();
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}
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else {
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glBegin(GL_POINTS);
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glVertex3f(x, y, z);
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glEnd();
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}
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}
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}
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/**
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* Top row of points rendered convetionally,
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* bottom row rendered with shaders.
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*/
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static void
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Redisplay(void)
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{
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glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
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if (Smooth)
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glEnable(GL_POINT_SMOOTH);
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else
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glDisable(GL_POINT_SMOOTH);
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if (Blend)
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glEnable(GL_BLEND);
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else
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glDisable(GL_BLEND);
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glPushMatrix();
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glTranslatef(Xpos, Ypos, 0);
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/*
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* regular points
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*/
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glPushMatrix();
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glTranslatef(0, 1.2, 0);
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glUseProgram_func(0);
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DrawPoints(GL_FALSE);
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glPopMatrix();
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/*
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* shader points
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*/
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glPushMatrix();
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glTranslatef(0, -1.2, 0);
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glUseProgram_func(Program);
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if (uViewportInv != -1) {
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glUniform2f_func(uViewportInv, 1.0 / WinWidth, 1.0 / WinHeight);
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}
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DrawPoints(GL_TRUE);
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glPopMatrix();
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glPopMatrix();
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glutSwapBuffers();
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}
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static void
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Reshape(int width, int height)
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{
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WinWidth = width;
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WinHeight = height;
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glViewport(0, 0, width, height);
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glMatrixMode(GL_PROJECTION);
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glLoadIdentity();
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glFrustum(-1.0, 1.0, -1.0, 1.0, 4.0, 30.0);
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glMatrixMode(GL_MODELVIEW);
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glLoadIdentity();
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glTranslatef(0.0f, 0.0f, -20.0f);
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}
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static void
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Key(unsigned char key, int x, int y)
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{
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(void) x;
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(void) y;
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switch(key) {
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case 'b':
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Blend = !Blend;
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break;
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case 's':
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Smooth = !Smooth;
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break;
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case 27:
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glDeleteShader_func(FragShader);
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glDeleteShader_func(VertShader);
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glDeleteProgram_func(Program);
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glutDestroyWindow(Win);
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exit(0);
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}
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glutPostRedisplay();
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}
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static void
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SpecialKey(int key, int x, int y)
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{
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const GLfloat step = 1/100.0;
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switch(key) {
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case GLUT_KEY_UP:
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Ypos += step;
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break;
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case GLUT_KEY_DOWN:
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Ypos -= step;
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break;
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case GLUT_KEY_LEFT:
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Xpos -= step;
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break;
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case GLUT_KEY_RIGHT:
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Xpos += step;
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break;
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}
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glutPostRedisplay();
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}
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static void
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Init(void)
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{
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/* Fragment shader: compute distance of fragment from center of point
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* (we're using texcoords but another varying could be used).
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* if dist > 1, discard (coverage==0)
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* if dist < k, coverage = 1
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* else, coverage = func(dist)
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* Note: length() uses sqrt() and may be expensive. The distance could
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* be squared instead (with adjustments to the threshold (k) test)
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*/
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static const char *fragShaderText =
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"void main() {\n"
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" float cover; \n"
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" float k = 2.0 / gl_Point.size; \n"
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" float d = length(gl_TexCoord[0].xy); \n"
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" if (d >= 1.0) \n"
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" discard; \n"
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" if (d < 1.0 - k) \n"
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" cover = 1.0; \n"
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" else \n"
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" cover = (1.0 - d) * 0.5 * gl_Point.size; \n"
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" gl_FragColor.rgb = gl_Color.rgb; \n"
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" gl_FragColor.a = cover; \n"
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"}\n";
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/* Vertex shader: compute new vertex position based on incoming vertex pos,
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* texcoords, point size, and inverse viewport scale factor.
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* Note: should compute point size attenuation here too.
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*/
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static const char *vertShaderText =
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"uniform vec2 viewportInv; \n"
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"void main() {\n"
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" vec4 pos = gl_ModelViewProjectionMatrix * gl_Vertex;\n"
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" gl_Position.xy = pos.xy + gl_MultiTexCoord0.xy * viewportInv \n"
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" * gl_Point.size * pos.w; \n"
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" gl_Position.zw = pos.zw; \n"
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" gl_TexCoord[0] = gl_MultiTexCoord0; \n"
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" gl_FrontColor = gl_Color; \n"
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"}\n";
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if (!ShadersSupported())
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exit(1);
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GetExtensionFuncs();
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VertShader = CompileShaderText(GL_VERTEX_SHADER, vertShaderText);
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FragShader = CompileShaderText(GL_FRAGMENT_SHADER, fragShaderText);
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Program = LinkShaders(VertShader, FragShader);
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glUseProgram_func(Program);
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uViewportInv = glGetUniformLocation_func(Program, "viewportInv");
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glUseProgram_func(0);
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glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
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}
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int
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main(int argc, char *argv[])
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{
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glutInit(&argc, argv);
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glutInitWindowSize(WinWidth, WinHeight);
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glutInitDisplayMode(GLUT_RGB | GLUT_DOUBLE | GLUT_DEPTH);
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Win = glutCreateWindow(argv[0]);
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glutReshapeFunc(Reshape);
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glutKeyboardFunc(Key);
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glutSpecialFunc(SpecialKey);
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glutDisplayFunc(Redisplay);
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Init();
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glutMainLoop();
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return 0;
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}
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