progs/glsl/trirast.c

   1 /**
   2  * Demonstration of doing triangle rasterization with a fragment program.
   3  * Basic idea:
   4  *   1. Draw screen-aligned quad / bounding box around the triangle verts.
   5  *   2. For each pixel in the quad, determine if pixel is inside/outside
   6  *      the triangle edges.
   7  *
   8  * Brian Paul
   9  * 1 Aug 2007
  10  */
  11
  12
  13 #include <assert.h>
  14 #include <string.h>
  15 #include <stdio.h>
  16 #include <stdlib.h>
  17 #include <math.h>
  18 #include <GL/gl.h>
  19 #include <GL/glut.h>
  20 #include <GL/glext.h>
  21 #include "extfuncs.h"
  22
  23
  24 static GLint WinWidth = 300, WinHeight = 300;
  25 static char *FragProgFile = NULL;
  26 static char *VertProgFile = NULL;
  27 static GLuint fragShader;
  28 static GLuint vertShader;
  29 static GLuint program;
  30 static GLint win = 0;
  31 static GLboolean anim = GL_TRUE;
  32 static GLfloat Zrot = 0.0f;
  33 static GLint uv0, uv1, uv2;
  34
  35
  36 static const GLfloat TriVerts[3][2] = {
  37    { 50,  50 },
  38    { 250, 50 },
  39    { 150, 250 }
  40 };
  41
  42
  43 static void
  44 RotateVerts(GLfloat a,
  45             GLuint n, const GLfloat vertsIn[][2], GLfloat vertsOut[][2])
  46 {
  47    GLuint i;
  48    GLfloat cx = WinWidth / 2, cy = WinHeight / 2;
  49    for (i = 0; i < n; i++) {
  50       float x = vertsIn[i][0] - cx;
  51       float y = vertsIn[i][1] - cy;
  52
  53       vertsOut[i][0] =  x * cos(a) + y * sin(a)  + cx;
  54       vertsOut[i][1] = -x * sin(a) + y * cos(a)  + cy;
  55    }
  56 }
  57
  58 static void
  59 ComputeBounds(GLuint n, GLfloat vertsIn[][2],
  60               GLfloat *xmin, GLfloat *ymin,
  61               GLfloat *xmax, GLfloat *ymax)
  62 {
  63    GLuint i;
  64    *xmin = *xmax = vertsIn[0][0];
  65    *ymin = *ymax = vertsIn[0][1];
  66    for (i = 1; i < n; i++) {
  67       if (vertsIn[i][0] < *xmin)
  68          *xmin = vertsIn[i][0];
  69       else if (vertsIn[i][0] > *xmax)
  70          *xmax = vertsIn[i][0];
  71       if (vertsIn[i][1] < *ymin)
  72          *ymin = vertsIn[i][1];
  73       else if (vertsIn[i][1] > *ymax)
  74          *ymax = vertsIn[i][1];
  75    }
  76 }
  77
  78
  79 static void
  80 Redisplay(void)
  81 {
  82    GLfloat v[3][2], xmin, ymin, xmax, ymax;
  83
  84    RotateVerts(Zrot, 3, TriVerts, v);
  85    ComputeBounds(3, v, &xmin, &ymin, &xmax, &ymax);
  86
  87    glUniform2fv_func(uv0, 1, v[0]);
  88    glUniform2fv_func(uv1, 1, v[1]);
  89    glUniform2fv_func(uv2, 1, v[2]);
  90
  91    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
  92
  93    glPushMatrix();
  94    glBegin(GL_POLYGON);
  95    glVertex2f(xmin, ymin);
  96    glVertex2f(xmax, ymin);
  97    glVertex2f(xmax, ymax);
  98    glVertex2f(xmin, ymax);
  99    glEnd();
 100    glPopMatrix();
 101
 102    glutSwapBuffers();
 103 }
 104
 105
 106 static void
 107 Idle(void)
 108 {
 109    Zrot = glutGet(GLUT_ELAPSED_TIME) * 0.0005;
 110    glutPostRedisplay();
 111 }
 112
 113
 114 static void
 115 Reshape(int width, int height)
 116 {
 117    glViewport(0, 0, width, height);
 118    glMatrixMode(GL_PROJECTION);
 119    glLoadIdentity();
 120    glOrtho(0, width, 0, height, -1, 1);
 121
 122    glMatrixMode(GL_MODELVIEW);
 123    glLoadIdentity();
 124 }
 125
 126
 127 static void
 128 CleanUp(void)
 129 {
 130    glDeleteShader_func(fragShader);
 131    glDeleteShader_func(vertShader);
 132    glDeleteProgram_func(program);
 133    glutDestroyWindow(win);
 134 }
 135
 136
 137 static void
 138 Key(unsigned char key, int x, int y)
 139 {
 140   (void) x;
 141   (void) y;
 142
 143    switch(key) {
 144    case ' ':
 145    case 'a':
 146       anim = !anim;
 147       if (anim)
 148          glutIdleFunc(Idle);
 149       else
 150          glutIdleFunc(NULL);
 151       break;
 152    case 27:
 153       CleanUp();
 154       exit(0);
 155       break;
 156    }
 157    glutPostRedisplay();
 158 }
 159
 160
 161 static void
 162 LoadAndCompileShader(GLuint shader, const char *text)
 163 {
 164    GLint stat;
 165
 166    glShaderSource_func(shader, 1, (const GLchar **) &text, NULL);
 167
 168    glCompileShader_func(shader);
 169
 170    glGetShaderiv_func(shader, GL_COMPILE_STATUS, &stat);
 171    if (!stat) {
 172       GLchar log[1000];
 173       GLsizei len;
 174       glGetShaderInfoLog_func(shader, 1000, &len, log);
 175       fprintf(stderr, "fslight: problem compiling shader:\n%s\n", log);
 176       exit(1);
 177    }
 178 }
 179
 180
 181 /**
 182  * Read a shader from a file.
 183  */
 184 static void
 185 ReadShader(GLuint shader, const char *filename)
 186 {
 187    const int max = 100*1000;
 188    int n;
 189    char *buffer = (char*) malloc(max);
 190    FILE *f = fopen(filename, "r");
 191    if (!f) {
 192       fprintf(stderr, "fslight: Unable to open shader file %s\n", filename);
 193       exit(1);
 194    }
 195
 196    n = fread(buffer, 1, max, f);
 197    printf("fslight: read %d bytes from shader file %s\n", n, filename);
 198    if (n > 0) {
 199       buffer[n] = 0;
 200       LoadAndCompileShader(shader, buffer);
 201    }
 202
 203    fclose(f);
 204    free(buffer);
 205 }
 206
 207
 208 static void
 209 CheckLink(GLuint prog)
 210 {
 211    GLint stat;
 212    glGetProgramiv_func(prog, GL_LINK_STATUS, &stat);
 213    if (!stat) {
 214       GLchar log[1000];
 215       GLsizei len;
 216       glGetProgramInfoLog_func(prog, 1000, &len, log);
 217       fprintf(stderr, "Linker error:\n%s\n", log);
 218    }
 219 }
 220
 221
 222 static void
 223 Init(void)
 224 {
 225    static const char *fragShaderText =
 226       "uniform vec2 v0, v1, v2; \n"
 227       "float crs(const vec2 u, const vec2 v) \n"
 228       "{ \n"
 229       "   return u.x * v.y - u.y * v.x; \n"
 230       "} \n"
 231       "\n"
 232       "void main() {\n"
 233       "   vec2 p = gl_FragCoord.xy; \n"
 234       "   if (crs(v1 - v0, p - v0) >= 0 && \n"
 235       "       crs(v2 - v1, p - v1) >= 0 && \n"
 236       "       crs(v0 - v2, p - v2) >= 0) \n"
 237       "      gl_FragColor = vec4(1.0); \n"
 238       "   else \n"
 239       "      gl_FragColor = vec4(0.5); \n"
 240       "}\n";
 241    static const char *vertShaderText =
 242       "void main() {\n"
 243       "   gl_Position = gl_ModelViewProjectionMatrix * gl_Vertex;\n"
 244       "}\n";
 245    const char *version;
 246
 247    version = (const char *) glGetString(GL_VERSION);
 248    if (version[0] != '2' || version[1] != '.') {
 249       printf("This program requires OpenGL 2.x, found %s\n", version);
 250       exit(1);
 251    }
 252
 253    GetExtensionFuncs();
 254
 255    fragShader = glCreateShader_func(GL_FRAGMENT_SHADER);
 256    if (FragProgFile)
 257       ReadShader(fragShader, FragProgFile);
 258    else
 259       LoadAndCompileShader(fragShader, fragShaderText);
 260
 261    vertShader = glCreateShader_func(GL_VERTEX_SHADER);
 262    if (VertProgFile)
 263       ReadShader(vertShader, VertProgFile);
 264    else
 265       LoadAndCompileShader(vertShader, vertShaderText);
 266
 267    program = glCreateProgram_func();
 268    glAttachShader_func(program, fragShader);
 269    glAttachShader_func(program, vertShader);
 270    glLinkProgram_func(program);
 271    CheckLink(program);
 272    glUseProgram_func(program);
 273
 274    uv0 = glGetUniformLocation_func(program, "v0");
 275    uv1 = glGetUniformLocation_func(program, "v1");
 276    uv2 = glGetUniformLocation_func(program, "v2");
 277    printf("Uniforms: %d %d %d\n", uv0, uv1, uv2);
 278
 279    /*assert(glGetError() == 0);*/
 280
 281    glClearColor(0.3f, 0.3f, 0.3f, 0.0f);
 282    glEnable(GL_DEPTH_TEST);
 283
 284    printf("GL_RENDERER = %s\n",(const char *) glGetString(GL_RENDERER));
 285
 286    assert(glIsProgram_func(program));
 287    assert(glIsShader_func(fragShader));
 288    assert(glIsShader_func(vertShader));
 289
 290    glColor3f(1, 0, 0);
 291 }
 292
 293
 294 static void
 295 ParseOptions(int argc, char *argv[])
 296 {
 297    int i;
 298    for (i = 1; i < argc; i++) {
 299       if (strcmp(argv[i], "-fs") == 0) {
 300          FragProgFile = argv[i+1];
 301       }
 302       else if (strcmp(argv[i], "-vs") == 0) {
 303          VertProgFile = argv[i+1];
 304       }
 305    }
 306 }
 307
 308
 309 int
 310 main(int argc, char *argv[])
 311 {
 312    glutInit(&argc, argv);
 313    glutInitWindowPosition( 0, 0);
 314    glutInitWindowSize(WinWidth, WinHeight);
 315    glutInitDisplayMode(GLUT_RGB | GLUT_DOUBLE | GLUT_DEPTH);
 316    win = glutCreateWindow(argv[0]);
 317    glutReshapeFunc(Reshape);
 318    glutKeyboardFunc(Key);
 319    glutDisplayFunc(Redisplay);
 320    if (anim)
 321       glutIdleFunc(Idle);
 322    ParseOptions(argc, argv);
 323    Init();
 324    glutMainLoop();
 325    return 0;
 326 }