triangle rasterization with frag shader

1 files changed, 326 insertions, 0 deletions

diff --git a/progs/glsl/trirast.c b/progs/glsl/trirast.c
new file mode 100644
index 0000000000..e4325deb1f
--- /dev/null
+++ b/progs/glsl/trirast.c
@@ -0,0 +1,326 @@
+/**
+ * Demonstration of doing triangle rasterization with a fragment program.
+ * Basic idea:
+ *   1. Draw screen-aligned quad / bounding box around the triangle verts.
+ *   2. For each pixel in the quad, determine if pixel is inside/outside
+ *      the triangle edges.
+ *
+ * Brian Paul
+ * 1 Aug 2007
+ */
+
+
+#include <assert.h>
+#include <string.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <math.h>
+#include <GL/gl.h>
+#include <GL/glut.h>
+#include <GL/glext.h>
+#include "extfuncs.h"
+
+
+static GLint WinWidth = 300, WinHeight = 300;
+static char *FragProgFile = NULL;
+static char *VertProgFile = NULL;
+static GLuint fragShader;
+static GLuint vertShader;
+static GLuint program;
+static GLint win = 0;
+static GLboolean anim = GL_TRUE;
+static GLfloat Zrot = 0.0f;
+static GLint uv0, uv1, uv2;
+
+
+static const GLfloat TriVerts[3][2] = {
+   { 50,  50 },
+   { 250, 50 },
+   { 150, 250 }
+};
+
+
+static void
+RotateVerts(GLfloat a,
+            GLuint n, const GLfloat vertsIn[][2], GLfloat vertsOut[][2])
+{
+   GLuint i;
+   GLfloat cx = WinWidth / 2, cy = WinHeight / 2;
+   for (i = 0; i < n; i++) {
+      float x = vertsIn[i][0] - cx;
+      float y = vertsIn[i][1] - cy;
+      
+      vertsOut[i][0] =  x * cos(a) + y * sin(a)  + cx;
+      vertsOut[i][1] = -x * sin(a) + y * cos(a)  + cy;
+   }
+}
+
+static void
+ComputeBounds(GLuint n, GLfloat vertsIn[][2],
+              GLfloat *xmin, GLfloat *ymin,
+              GLfloat *xmax, GLfloat *ymax)
+{
+   GLuint i;
+   *xmin = *xmax = vertsIn[0][0];
+   *ymin = *ymax = vertsIn[0][1];
+   for (i = 1; i < n; i++) {
+      if (vertsIn[i][0] < *xmin)
+         *xmin = vertsIn[i][0];
+      else if (vertsIn[i][0] > *xmax)
+         *xmax = vertsIn[i][0];
+      if (vertsIn[i][1] < *ymin)
+         *ymin = vertsIn[i][1];
+      else if (vertsIn[i][1] > *ymax)
+         *ymax = vertsIn[i][1];
+   }
+}
+
+
+static void
+Redisplay(void)
+{
+   GLfloat v[3][2], xmin, ymin, xmax, ymax;
+
+   RotateVerts(Zrot, 3, TriVerts, v);
+   ComputeBounds(3, v, &xmin, &ymin, &xmax, &ymax);
+
+   glUniform2fv_func(uv0, 1, v[0]);
+   glUniform2fv_func(uv1, 1, v[1]);
+   glUniform2fv_func(uv2, 1, v[2]);
+
+   glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
+
+   glPushMatrix();
+   glBegin(GL_POLYGON);
+   glVertex2f(xmin, ymin);
+   glVertex2f(xmax, ymin);
+   glVertex2f(xmax, ymax);
+   glVertex2f(xmin, ymax);
+   glEnd();
+   glPopMatrix();
+
+   glutSwapBuffers();
+}
+
+
+static void
+Idle(void)
+{
+   Zrot = glutGet(GLUT_ELAPSED_TIME) * 0.0005;
+   glutPostRedisplay();
+}
+
+
+static void
+Reshape(int width, int height)
+{
+   glViewport(0, 0, width, height);
+   glMatrixMode(GL_PROJECTION);
+   glLoadIdentity();
+   glOrtho(0, width, 0, height, -1, 1);
+
+   glMatrixMode(GL_MODELVIEW);
+   glLoadIdentity();
+}
+
+
+static void
+CleanUp(void)
+{
+   glDeleteShader_func(fragShader);
+   glDeleteShader_func(vertShader);
+   glDeleteProgram_func(program);
+   glutDestroyWindow(win);
+}
+
+
+static void
+Key(unsigned char key, int x, int y)
+{
+  (void) x;
+  (void) y;
+
+   switch(key) {
+   case ' ':
+   case 'a':
+      anim = !anim;
+      if (anim)
+         glutIdleFunc(Idle);
+      else
+         glutIdleFunc(NULL);
+      break;
+   case 27:
+      CleanUp();
+      exit(0);
+      break;
+   }
+   glutPostRedisplay();
+}
+
+
+static void
+LoadAndCompileShader(GLuint shader, const char *text)
+{
+   GLint stat;
+
+   glShaderSource_func(shader, 1, (const GLchar **) &text, NULL);
+
+   glCompileShader_func(shader);
+
+   glGetShaderiv_func(shader, GL_COMPILE_STATUS, &stat);
+   if (!stat) {
+      GLchar log[1000];
+      GLsizei len;
+      glGetShaderInfoLog_func(shader, 1000, &len, log);
+      fprintf(stderr, "fslight: problem compiling shader:\n%s\n", log);
+      exit(1);
+   }
+}
+
+
+/**
+ * Read a shader from a file.
+ */
+static void
+ReadShader(GLuint shader, const char *filename)
+{
+   const int max = 100*1000;
+   int n;
+   char *buffer = (char*) malloc(max);
+   FILE *f = fopen(filename, "r");
+   if (!f) {
+      fprintf(stderr, "fslight: Unable to open shader file %s\n", filename);
+      exit(1);
+   }
+
+   n = fread(buffer, 1, max, f);
+   printf("fslight: read %d bytes from shader file %s\n", n, filename);
+   if (n > 0) {
+      buffer[n] = 0;
+      LoadAndCompileShader(shader, buffer);
+   }
+
+   fclose(f);
+   free(buffer);
+}
+
+
+static void
+CheckLink(GLuint prog)
+{
+   GLint stat;
+   glGetProgramiv_func(prog, GL_LINK_STATUS, &stat);
+   if (!stat) {
+      GLchar log[1000];
+      GLsizei len;
+      glGetProgramInfoLog_func(prog, 1000, &len, log);
+      fprintf(stderr, "Linker error:\n%s\n", log);
+   }
+}
+
+
+static void
+Init(void)
+{
+   static const char *fragShaderText =
+      "uniform vec2 v0, v1, v2; \n"
+      "float crs(const vec2 u, const vec2 v) \n"
+      "{ \n"
+      "   return u.x * v.y - u.y * v.x; \n"
+      "} \n"
+      "\n"
+      "void main() {\n"
+      "   vec2 p = gl_FragCoord.xy; \n"
+      "   if (crs(v1 - v0, p - v0) >= 0 && \n"
+      "       crs(v2 - v1, p - v1) >= 0 && \n"
+      "       crs(v0 - v2, p - v2) >= 0) \n"
+      "      gl_FragColor = vec4(1.0); \n"
+      "   else \n"
+      "      gl_FragColor = vec4(0.5); \n"
+      "}\n";
+   static const char *vertShaderText =
+      "void main() {\n"
+      "   gl_Position = gl_ModelViewProjectionMatrix * gl_Vertex;\n"
+      "}\n";
+   const char *version;
+
+   version = (const char *) glGetString(GL_VERSION);
+   if (version[0] != '2' || version[1] != '.') {
+      printf("This program requires OpenGL 2.x, found %s\n", version);
+      exit(1);
+   }
+
+   GetExtensionFuncs();
+
+   fragShader = glCreateShader_func(GL_FRAGMENT_SHADER);
+   if (FragProgFile)
+      ReadShader(fragShader, FragProgFile);
+   else
+      LoadAndCompileShader(fragShader, fragShaderText);
+
+   vertShader = glCreateShader_func(GL_VERTEX_SHADER);
+   if (VertProgFile)
+      ReadShader(vertShader, VertProgFile);
+   else
+      LoadAndCompileShader(vertShader, vertShaderText);
+
+   program = glCreateProgram_func();
+   glAttachShader_func(program, fragShader);
+   glAttachShader_func(program, vertShader);
+   glLinkProgram_func(program);
+   CheckLink(program);
+   glUseProgram_func(program);
+
+   uv0 = glGetUniformLocation_func(program, "v0");
+   uv1 = glGetUniformLocation_func(program, "v1");
+   uv2 = glGetUniformLocation_func(program, "v2");
+   printf("Uniforms: %d %d %d\n", uv0, uv1, uv2);
+
+   /*assert(glGetError() == 0);*/
+
+   glClearColor(0.3f, 0.3f, 0.3f, 0.0f);
+   glEnable(GL_DEPTH_TEST);
+
+   printf("GL_RENDERER = %s\n",(const char *) glGetString(GL_RENDERER));
+
+   assert(glIsProgram_func(program));
+   assert(glIsShader_func(fragShader));
+   assert(glIsShader_func(vertShader));
+
+   glColor3f(1, 0, 0);
+}
+
+
+static void
+ParseOptions(int argc, char *argv[])
+{
+   int i;
+   for (i = 1; i < argc; i++) {
+      if (strcmp(argv[i], "-fs") == 0) {
+         FragProgFile = argv[i+1];
+      }
+      else if (strcmp(argv[i], "-vs") == 0) {
+         VertProgFile = argv[i+1];
+      }
+   }
+}
+
+
+int
+main(int argc, char *argv[])
+{
+   glutInit(&argc, argv);
+   glutInitWindowPosition( 0, 0);
+   glutInitWindowSize(WinWidth, WinHeight);
+   glutInitDisplayMode(GLUT_RGB | GLUT_DOUBLE | GLUT_DEPTH);
+   win = glutCreateWindow(argv[0]);
+   glutReshapeFunc(Reshape);
+   glutKeyboardFunc(Key);
+   glutDisplayFunc(Redisplay);
+   if (anim)
+      glutIdleFunc(Idle);
+   ParseOptions(argc, argv);
+   Init();
+   glutMainLoop();
+   return 0;
+}