gistfile1.txt

// Some old PNG screenshot code that I used in a Ruby binding.

static VALUE
rbas_screen_shot(VALUE self, VALUE filename)
{
	int bytes = AS_SCREEN_W * AS_SCREEN_H * 3;
	GLubyte pixels[bytes];
	glReadPixels(0, 0, AS_SCREEN_W, AS_SCREEN_H, GL_RGB, GL_UNSIGNED_BYTE, pixels);
	
	char *name = StringValuePtr(filename);
	FILE *png_file = fopen(name, "wb");
	if(!png_file)
					rb_raise(rb_eRuntimeError, "\"%s\" could not be opened for writing.", name);
	
	png_structp png_ptr = png_create_write_struct(PNG_LIBPNG_VER_STRING, NULL, NULL, NULL);
	if(!png_ptr)
					rb_raise(rb_eRuntimeError, "LibPNG error when saving \"%s\".", name);
	
	
	png_infop info_ptr = png_create_info_struct(png_ptr);
	if(!info_ptr)
					rb_raise(rb_eRuntimeError, "LibPNG error when saving \"%s\".", name);
	
	if(setjmp(png_jmpbuf(png_ptr)))
					rb_raise(rb_eRuntimeError, "LibPNG error when saving \"%s\".", name);
	
	png_init_io(png_ptr, png_file);
	
	png_set_IHDR(png_ptr, info_ptr, AS_SCREEN_W, AS_SCREEN_H,
							 8, PNG_COLOR_TYPE_RGB, PNG_INTERLACE_NONE,
							 PNG_COMPRESSION_TYPE_DEFAULT, PNG_FILTER_TYPE_DEFAULT);
	
	png_byte* row_ptrs[AS_SCREEN_H];
	
	int i;
	for (i=0; i<AS_SCREEN_H; i++)
					row_ptrs[i] = pixels + (AS_SCREEN_H - 1 - i)*(AS_SCREEN_W*3);
	
	png_set_rows(png_ptr, info_ptr, row_ptrs);
	png_write_png(png_ptr, info_ptr, PNG_TRANSFORM_IDENTITY, NULL);
	
	png_destroy_write_struct(&png_ptr, &info_ptr);
	fclose(png_file);
	
	return Qnil;
}