func apply_surface(x, y int16, src, dest *sdl.Surface) {
var offset sdl.Rect
offset.X = x
offset.Y = y
dest.Blit(&offset, src, nil)
}
func (renderer *SDLRenderer) addUpdatedRect(rect *sdl.Rect) {
visibleX, visibleY := renderer.transformToVisibleXY(int(rect.X), int(rect.Y))
visibleRect := sdl.Rect{int16(visibleX), int16(visibleY), rect.W, rect.H}
if visibleRect.Y > int16(renderer.height) {
visibleRect.Y = int16(renderer.height)
}
if visibleRect.Y < 0 {
visibleRect.Y = 0
}
if visibleRect.H > uint16(renderer.height) {
visibleRect.H = uint16(renderer.height)
}
renderer.updatedRects = append(renderer.updatedRects, visibleRect)
}