PPM screenshot with GLUT

glut_ppm.c

void TakeScreenshot(const char *fname)
{
  printf("writing a screenshot to %s\n", fname);

  int dimx = glutGet(GLUT_WINDOW_WIDTH);
  int dimy = glutGet(GLUT_WINDOW_HEIGHT);

  size_t imsize = 3*dimx*dimy;
  char *pixels = (char*) malloc(imsize*sizeof(char));
  glReadPixels(0, 0, dimx, dimy, GL_RGB, GL_UNSIGNED_BYTE, pixels);

  FILE *fp = fopen(fname, "wb");
  fprintf(fp, "P6\n%d %d\n255\n", dimx, dimy);
  fwrite(pixels, sizeof(char), imsize, fp);
  fclose(fp);

  free(pixels);
}