From kaszeta@me.umn.edu  Tue Apr 27 12:25:04 1999
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From: Richard Kaszeta <kaszeta@me.umn.edu>
To: curt@me.umn.edu
Subject: Screen Dump under OpenGL
Date: Tue, 27 Apr 1999 12:25:03 -0500 (CDT)

Dumps the framebuffer to a .ppm file:

#include <stdio.h>
#include <stdlib.h>
#include <limits.h>
#include <GL/glut.h>

#define RGB  3			/* 3 bytes of color info per pixel */
#define RGBA 4			/* 4 bytes of color+alpha info */

void my_glDumpWindow(const char * filename, int win_width, int win_height) {
  int i, j, k, q;
  GLubyte *buffer;
  unsigned char *ibuffer;
  FILE *fp;

  buffer = (GLubyte *) malloc(win_width*win_height*RGBA);
  ibuffer = (unsigned char *) malloc(win_width*win_height*RGB);

  /* read window contents from color buffer with glReadPixels */
  glFinish();
  glReadPixels(0, 0, win_width, win_height, GL_RGBA, GL_UNSIGNED_BYTE, buffer);

  fp = fopen(filename, "w");
  fprintf(fp, "P6\n# CREATOR: glReadPixel()\n%d %d\n%d\n",
          win_width, win_height, UCHAR_MAX);
  q = 0;
  for (i = 0; i < win_height; i++)
    for (j = 0; j < win_width; j++)
      for (k = 0; k < RGB; k++)
        ibuffer[q++] = (unsigned char)
          *(buffer + (RGBA*((win_height-1-i)*win_width+j)+k));
  fwrite(ibuffer, sizeof(unsigned char), RGB*win_width*win_height, fp);
  fclose(fp);
  free(buffer);
  free(ibuffer);

  printf("wrote file (%d x %d pixels, %d bytes)\n",
         win_width, win_height, RGB*win_width*win_height);
}

-- 
Richard W Kaszeta 			PhD. Candidate and Sysadmin
bofh@me.umn.edu				University of MN, ME Dept
http://www.menet.umn.edu/~kaszeta