void tcanvas::blit(surface& surf, SDL_Rect rect)
{
    draw();

    if(blur_depth_) {
        if(is_neutral(surf)) {
            blur_surface(surf, rect, blur_depth_);
        } else {
            // Can't directly blur the surface if not 32 bpp.
            SDL_Rect r = rect;
            ///@todo we should use: get_surface_portion(surf, r, false)
            ///no need to optimize format, since blur_surface will undo it
            surface s = get_surface_portion(surf, r, true);
            s = blur_surface(s, blur_depth_);
            sdl_blit(s, NULL, surf, &rect);
        }
    }

    sdl_blit(canvas_, NULL, surf, &rect);
}