progs/trivial/readpixels.c

   1 /*
   2  * glRead/DrawPixels test
   3  */
   4
   5
   6 #include <GL/glew.h>
   7 #include <stdio.h>
   8 #include <string.h>
   9 #include <stdlib.h>
  10 #include <GL/glut.h>
  11
  12 static int Width = 250, Height = 250;
  13 static GLfloat Zoom = 1.0;
  14
  15 static void Init(void)
  16 {
  17    fprintf(stderr, "GL_RENDERER   = %s\n", (char *) glGetString(GL_RENDERER));
  18    fprintf(stderr, "GL_VERSION    = %s\n", (char *) glGetString(GL_VERSION));
  19    fprintf(stderr, "GL_VENDOR     = %s\n", (char *) glGetString(GL_VENDOR));
  20    fflush(stderr);
  21    glClearColor(0.3, 0.1, 0.3, 0.0);
  22 }
  23
  24 static void Reshape(int width, int height)
  25 {
  26    Width = width / 2;
  27    Height = height;
  28    /* draw on left half (we'll read that area) */
  29    glViewport(0, 0, Width, height);
  30    glMatrixMode(GL_PROJECTION);
  31    glLoadIdentity();
  32    glOrtho(-1.0, 1.0, -1.0, 1.0, -0.5, 1000.0);
  33    glMatrixMode(GL_MODELVIEW);
  34 }
  35
  36 static void Key(unsigned char key, int x, int y)
  37 {
  38    switch (key) {
  39    case 27:
  40       exit(0);
  41    default:
  42       break;
  43    }
  44    glutPostRedisplay();
  45 }
  46
  47 static void Draw(void)
  48 {
  49    GLfloat *image = (GLfloat *) malloc(Width * Height * 4 * sizeof(GLfloat));
  50
  51    glClear(GL_COLOR_BUFFER_BIT);
  52
  53    glBegin(GL_TRIANGLES);
  54    glColor3f(.8,0,0);
  55    glVertex3f(-0.9, -0.9, -30.0);
  56    glColor3f(0,.9,0);
  57    glVertex3f( 0.9, -0.9, -30.0);
  58    glColor3f(0,0,.7);
  59    glVertex3f( 0.0,  0.9, -30.0);
  60    glEnd();
  61
  62    glBegin(GL_QUADS);
  63    glColor3f(1, 1, 1);
  64    glVertex2f(-1.0, -1.0);
  65    glVertex2f(-0.9, -1.0);
  66    glVertex2f(-0.9, -0.9);
  67    glVertex2f(-1.0, -0.9);
  68    glEnd();
  69
  70    glReadPixels(0, 0, Width, Height, GL_RGBA, GL_FLOAT, image);
  71    printf("Pixel(0,0) = %f, %f, %f, %f\n",
  72           image[0], image[1], image[2], image[3]);
  73    /* draw to right half of window */
  74    glWindowPos2iARB(Width, 0);
  75    glPixelZoom(Zoom, Zoom);
  76    glDrawPixels(Width, Height, GL_RGBA, GL_FLOAT, image);
  77    free(image);
  78
  79    glutSwapBuffers();
  80 }
  81
  82 int main(int argc, char **argv)
  83 {
  84    glutInit(&argc, argv);
  85    glutInitWindowPosition(0, 0);
  86    glutInitWindowSize(Width*2, Height);
  87    glutInitDisplayMode(GLUT_RGB | GLUT_ALPHA | GLUT_DOUBLE);
  88    if (glutCreateWindow(argv[0]) == GL_FALSE) {
  89       exit(1);
  90    }
  91
  92    if (argc > 1)
  93       Zoom = atof(argv[1]);
  94
  95    glewInit();
  96
  97    Init();
  98
  99    glutReshapeFunc(Reshape);
 100    glutKeyboardFunc(Key);
 101    glutDisplayFunc(Draw);
 102    glutMainLoop();
 103    return 0;
 104 }