progs/trivial/readpixels.c

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