uint8_t *img = new uint8_t[w*h*3];
glGetTexImage(GL_TEXTURE_2D, 0, GL_RGB, GL_UNSIGNED_BYTE, img);
write_ppm(img, w, h, "%s", fn);
uint8_t *img = new uint8_t[w*h*3];
glGetTexImage(GL_TEXTURE_2D, 0, GL_RGB, GL_UNSIGNED_BYTE, img);
write_ppm(img, w, h, "%s", fn);