Board Thread:Questions and Answers/@comment-15974427-20140125213508/@comment-9531161-20140125220105

You can still use the GRP method (use GPUTCHR to draw the blocks from the SCR first, then the sprites on top of that), but it'll be very slow, and it'll be hard to move around. Plus, the window would have to line up directly with the background tiles, otherwise you'd incur yet another performance penalty.