Makes sure the given list of rectangles is updated on the given screen. +The rectangles must all be confined within the screen boundaries (no +clipping is done).
This function should not be called while screen is +locked.
Note: It is adviced to call this function only once per frame, since each +call has some processing overhead. This is no restriction since you +can pass any number of rectangles each time.
The rectangles are not automatically merged or checked for overlap. In +general, the programmer can use his knowledge about his particular +rectangles to merge them in an efficient way, to avoid overdraw.