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    if (anim) {
 110       Zrot = glutGet(GLUT_ELAPSED_TIME) * 0.0005;
 111       glutPostRedisplay();
 112    }
 113    else
 114       abort();
 115 }
 116
 117
 118 static void
 119 Reshape(int width, int height)
 120 {
 121    glViewport(0, 0, width, height);
 122    glMatrixMode(GL_PROJECTION);
 123    glLoadIdentity();
 124    glOrtho(0, width, 0, height, -1, 1);
 125
 126    glMatrixMode(GL_MODELVIEW);
 127    glLoadIdentity();
 128 }
 129
 130
 131 static void
 132 CleanUp(void)
 133 {
 134    glDeleteShader_func(fragShader);
 135    glDeleteShader_func(vertShader);
 136    glDeleteProgram_func(program);
 137    glutDestroyWindow(win);
 138 }
 139
 140
 141 static void
 142 Key(unsigned char key, int x, int y)
 143 {
 144   (void) x;
 145   (void) y;
 146
 147    switch(key) {
 148    case ' ':
 149    case 'a':
 150       anim = !anim;
 151       if (anim)
 152          glutIdleFunc(Idle);
 153       else
 154          glutIdleFunc(NULL);
 155       break;
 156    case 'z':
 157       Zrot = 0;
 158       break;
 159    case 's':
 160       Zrot += 0.05;
 161       break;
 162    case 27:
 163       CleanUp();
 164       exit(0);
 165       break;
 166    }
 167    glutPostRedisplay();
 168 }
 169
 170
 171 static void
 172 LoadAndCompileShader(GLuint shader, const char *text)
 173 {
 174    GLint stat;
 175
 176    glShaderSource_func(shader, 1, (const GLchar **) &text, NULL);
 177
 178    glCompileShader_func(shader);
 179
 180    glGetShaderiv_func(shader, GL_COMPILE_STATUS, &stat);
 181    if (!stat) {
 182       GLchar log[1000];
 183       GLsizei len;
 184       glGetShaderInfoLog_func(shader, 1000, &len, log);
 185       fprintf(stderr, "fslight: problem compiling shader:\n%s\n", log);
 186       exit(1);
 187    }
 188 }
 189
 190
 191 /**
 192  * Read a shader from a file.
 193  */
 194 static void
 195 ReadShader(GLuint shader, const char *filename)
 196 {
 197    const int max = 100*1000;
 198    int n;
 199    char *buffer = (char*) malloc(max);
 200    FILE *f = fopen(filename, "r");
 201    if (!f) {
 202       fprintf(stderr, "fslight: Unable to open shader file %s\n", filename);
 203       exit(1);
 204    }
 205
 206    n = fread(buffer, 1, max, f);
 207    printf("fslight: read %d bytes from shader file %s\n", n, filename);
 208    if (n > 0) {
 209       buffer[n] = 0;
 210       LoadAndCompileShader(shader, buffer);
 211    }
 212
 213    fclose(f);
 214    free(buffer);
 215 }
 216
 217
 218 static void
 219 CheckLink(GLuint prog)
 220 {
 221    GLint stat;
 222    glGetProgramiv_func(prog, GL_LINK_STATUS, &stat);
 223    if (!stat) {
 224       GLchar log[1000];
 225       GLsizei len;
 226       glGetProgramInfoLog_func(prog, 1000, &len, log);
 227       fprintf(stderr, "Linker error:\n%s\n", log);
 228    }
 229 }
 230
 231
 232 static void
 233 Init(void)
 234 {
 235    static const char *fragShaderText =
 236       "uniform vec2 v0, v1, v2; \n"
 237       "float crs(const vec2 u, const vec2 v) \n"
 238       "{ \n"
 239       "   return u.x * v.y - u.y * v.x; \n"
 240       "} \n"
 241       "\n"
 242       "void main() {\n"
 243       "   vec2 p = gl_FragCoord.xy; \n"
 244       "   if (crs(v1 - v0, p - v0) >= 0 && \n"
 245       "       crs(v2 - v1, p - v1) >= 0 && \n"
 246       "       crs(v0 - v2, p - v2) >= 0) \n"
 247       "      gl_FragColor = vec4(1.0); \n"
 248       "   else \n"
 249       "      gl_FragColor = vec4(0.5); \n"
 250       "}\n";
 251    static const char *vertShaderText =
 252       "void main() {\n"
 253       "   gl_Position = gl_ModelViewProjectionMatrix * gl_Vertex;\n"
 254       "}\n";
 255    const char *version;
 256
 257    version = (const char *) glGetString(GL_VERSION);
 258    if (version[0] != '2' || version[1] != '.') {
 259       printf("This program requires OpenGL 2.x, found %s\n", version);
 260       exit(1);
 261    }
 262
 263    GetExtensionFuncs();
 264
 265    fragShader = glCreateShader_func(GL_FRAGMENT_SHADER);
 266    if (FragProgFile)
 267       ReadShader(fragShader, FragProgFile);
 268    else
 269       LoadAndCompileShader(fragShader, fragShaderText);
 270
 271    vertShader = glCreateShader_func(GL_VERTEX_SHADER);
 272    if (VertProgFile)
 273       ReadShader(vertShader, VertProgFile);
 274    else
 275       LoadAndCompileShader(vertShader, vertShaderText);
 276
 277    program = glCreateProgram_func();
 278    glAttachShader_func(program, fragShader);
 279    glAttachShader_func(program, vertShader);
 280    glLinkProgram_func(program);
 281    CheckLink(program);
 282    glUseProgram_func(program);
 283
 284    uv0 = glGetUniformLocation_func(program, "v0");
 285    uv1 = glGetUniformLocation_func(program, "v1");
 286    uv2 = glGetUniformLocation_func(program, "v2");
 287    printf("Uniforms: %d %d %d\n", uv0, uv1, uv2);
 288
 289    /*assert(glGetError() == 0);*/
 290
 291    glClearColor(0.3f, 0.3f, 0.3f, 0.0f);
 292    glEnable(GL_DEPTH_TEST);
 293
 294    printf("GL_RENDERER = %s\n",(const char *) glGetString(GL_RENDERER));
 295
 296    assert(glIsProgram_func(program));
 297    assert(glIsShader_func(fragShader));
 298    assert(glIsShader_func(vertShader));
 299
 300    glColor3f(1, 0, 0);
 301 }
 302
 303
 304 static void
 305 ParseOptions(int argc, char *argv[])
 306 {
 307    int i;
 308    for (i = 1; i < argc; i++) {
 309       if (strcmp(argv[i], "-fs") == 0) {
 310          FragProgFile = argv[i+1];
 311       }
 312       else if (strcmp(argv[i], "-vs") == 0) {
 313          VertProgFile = argv[i+1];
 314       }
 315    }
 316 }
 317
 318
 319 int
 320 main(int argc, char *argv[])
 321 {
 322    glutInit(&argc, argv);
 323    glutInitWindowPosition( 0, 0);
 324    glutInitWindowSize(WinWidth, WinHeight);
 325    glutInitDisplayMode(GLUT_RGB | GLUT_DOUBLE | GLUT_DEPTH);
 326    win = glutCreateWindow(argv[0]);
 327    glutReshapeFunc(Reshape);
 328    glutKeyboardFunc(Key);
 329    glutDisplayFunc(Redisplay);
 330    if (anim)
 331       glutIdleFunc(Idle);
 332    ParseOptions(argc, argv);
 333    Init();
 334    glutMainLoop();
 335    return 0;
 336 }