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triangle rasterization with frag shader
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Brian
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commit
261eac3c79
1 changed files with 326 additions and 0 deletions
326
progs/glsl/trirast.c
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326
progs/glsl/trirast.c
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/**
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* Demonstration of doing triangle rasterization with a fragment program.
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* Basic idea:
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* 1. Draw screen-aligned quad / bounding box around the triangle verts.
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* 2. For each pixel in the quad, determine if pixel is inside/outside
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* the triangle edges.
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*
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* Brian Paul
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* 1 Aug 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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static GLint WinWidth = 300, WinHeight = 300;
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static char *FragProgFile = NULL;
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static char *VertProgFile = NULL;
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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 GLboolean anim = GL_TRUE;
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static GLfloat Zrot = 0.0f;
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static GLint uv0, uv1, uv2;
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static const GLfloat TriVerts[3][2] = {
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{ 50, 50 },
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{ 250, 50 },
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{ 150, 250 }
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};
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static void
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RotateVerts(GLfloat a,
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GLuint n, const GLfloat vertsIn[][2], GLfloat vertsOut[][2])
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{
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GLuint i;
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GLfloat cx = WinWidth / 2, cy = WinHeight / 2;
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for (i = 0; i < n; i++) {
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float x = vertsIn[i][0] - cx;
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float y = vertsIn[i][1] - cy;
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vertsOut[i][0] = x * cos(a) + y * sin(a) + cx;
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vertsOut[i][1] = -x * sin(a) + y * cos(a) + cy;
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}
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}
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static void
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ComputeBounds(GLuint n, GLfloat vertsIn[][2],
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GLfloat *xmin, GLfloat *ymin,
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GLfloat *xmax, GLfloat *ymax)
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{
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GLuint i;
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*xmin = *xmax = vertsIn[0][0];
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*ymin = *ymax = vertsIn[0][1];
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for (i = 1; i < n; i++) {
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if (vertsIn[i][0] < *xmin)
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*xmin = vertsIn[i][0];
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else if (vertsIn[i][0] > *xmax)
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*xmax = vertsIn[i][0];
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if (vertsIn[i][1] < *ymin)
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*ymin = vertsIn[i][1];
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else if (vertsIn[i][1] > *ymax)
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*ymax = vertsIn[i][1];
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}
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}
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static void
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Redisplay(void)
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{
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GLfloat v[3][2], xmin, ymin, xmax, ymax;
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RotateVerts(Zrot, 3, TriVerts, v);
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ComputeBounds(3, v, &xmin, &ymin, &xmax, &ymax);
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glUniform2fv_func(uv0, 1, v[0]);
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glUniform2fv_func(uv1, 1, v[1]);
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glUniform2fv_func(uv2, 1, v[2]);
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glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
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glPushMatrix();
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glBegin(GL_POLYGON);
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glVertex2f(xmin, ymin);
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glVertex2f(xmax, ymin);
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glVertex2f(xmax, ymax);
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glVertex2f(xmin, ymax);
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glEnd();
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glPopMatrix();
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glutSwapBuffers();
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}
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static void
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Idle(void)
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{
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Zrot = glutGet(GLUT_ELAPSED_TIME) * 0.0005;
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glutPostRedisplay();
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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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glViewport(0, 0, width, height);
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glMatrixMode(GL_PROJECTION);
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glLoadIdentity();
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glOrtho(0, width, 0, height, -1, 1);
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glMatrixMode(GL_MODELVIEW);
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glLoadIdentity();
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}
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static void
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CleanUp(void)
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{
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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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}
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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 ' ':
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case 'a':
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anim = !anim;
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if (anim)
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glutIdleFunc(Idle);
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else
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glutIdleFunc(NULL);
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break;
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case 27:
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CleanUp();
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exit(0);
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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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LoadAndCompileShader(GLuint shader, const char *text)
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{
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GLint stat;
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glShaderSource_func(shader, 1, (const GLchar **) &text, NULL);
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glCompileShader_func(shader);
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glGetShaderiv_func(shader, GL_COMPILE_STATUS, &stat);
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if (!stat) {
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GLchar log[1000];
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GLsizei len;
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glGetShaderInfoLog_func(shader, 1000, &len, log);
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fprintf(stderr, "fslight: problem compiling shader:\n%s\n", log);
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exit(1);
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}
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}
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/**
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* Read a shader from a file.
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*/
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static void
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ReadShader(GLuint shader, const char *filename)
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{
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const int max = 100*1000;
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int n;
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char *buffer = (char*) malloc(max);
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FILE *f = fopen(filename, "r");
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if (!f) {
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fprintf(stderr, "fslight: Unable to open shader file %s\n", filename);
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exit(1);
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}
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n = fread(buffer, 1, max, f);
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printf("fslight: read %d bytes from shader file %s\n", n, filename);
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if (n > 0) {
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buffer[n] = 0;
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LoadAndCompileShader(shader, buffer);
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}
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fclose(f);
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free(buffer);
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}
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static void
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CheckLink(GLuint prog)
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{
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GLint stat;
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glGetProgramiv_func(prog, GL_LINK_STATUS, &stat);
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if (!stat) {
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GLchar log[1000];
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GLsizei len;
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glGetProgramInfoLog_func(prog, 1000, &len, log);
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fprintf(stderr, "Linker error:\n%s\n", log);
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}
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}
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static void
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Init(void)
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{
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static const char *fragShaderText =
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"uniform vec2 v0, v1, v2; \n"
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"float crs(const vec2 u, const vec2 v) \n"
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"{ \n"
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" return u.x * v.y - u.y * v.x; \n"
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"} \n"
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"\n"
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"void main() {\n"
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" vec2 p = gl_FragCoord.xy; \n"
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" if (crs(v1 - v0, p - v0) >= 0 && \n"
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" crs(v2 - v1, p - v1) >= 0 && \n"
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" crs(v0 - v2, p - v2) >= 0) \n"
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" gl_FragColor = vec4(1.0); \n"
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" else \n"
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" gl_FragColor = vec4(0.5); \n"
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"}\n";
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static const char *vertShaderText =
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"void main() {\n"
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" gl_Position = gl_ModelViewProjectionMatrix * gl_Vertex;\n"
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"}\n";
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const char *version;
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version = (const char *) glGetString(GL_VERSION);
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if (version[0] != '2' || version[1] != '.') {
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printf("This program requires OpenGL 2.x, found %s\n", version);
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exit(1);
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}
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GetExtensionFuncs();
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fragShader = glCreateShader_func(GL_FRAGMENT_SHADER);
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if (FragProgFile)
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ReadShader(fragShader, FragProgFile);
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else
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LoadAndCompileShader(fragShader, fragShaderText);
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vertShader = glCreateShader_func(GL_VERTEX_SHADER);
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if (VertProgFile)
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ReadShader(vertShader, VertProgFile);
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else
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LoadAndCompileShader(vertShader, vertShaderText);
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program = glCreateProgram_func();
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glAttachShader_func(program, fragShader);
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glAttachShader_func(program, vertShader);
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glLinkProgram_func(program);
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CheckLink(program);
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glUseProgram_func(program);
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uv0 = glGetUniformLocation_func(program, "v0");
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uv1 = glGetUniformLocation_func(program, "v1");
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uv2 = glGetUniformLocation_func(program, "v2");
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printf("Uniforms: %d %d %d\n", uv0, uv1, uv2);
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/*assert(glGetError() == 0);*/
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glClearColor(0.3f, 0.3f, 0.3f, 0.0f);
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glEnable(GL_DEPTH_TEST);
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printf("GL_RENDERER = %s\n",(const char *) glGetString(GL_RENDERER));
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assert(glIsProgram_func(program));
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assert(glIsShader_func(fragShader));
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assert(glIsShader_func(vertShader));
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glColor3f(1, 0, 0);
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}
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static void
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ParseOptions(int argc, char *argv[])
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{
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int i;
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for (i = 1; i < argc; i++) {
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if (strcmp(argv[i], "-fs") == 0) {
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FragProgFile = argv[i+1];
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}
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else if (strcmp(argv[i], "-vs") == 0) {
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VertProgFile = argv[i+1];
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}
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}
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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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glutInitWindowPosition( 0, 0);
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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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glutDisplayFunc(Redisplay);
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if (anim)
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glutIdleFunc(Idle);
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ParseOptions(argc, argv);
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Init();
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glutMainLoop();
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return 0;
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}
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