Originally Posted by Mrs Beanbag
If the background image is also a tilemap. On Mr Beanbag it's not, it's just a single large image that wraps around, not sure about Chuck Rock though.
Chuck Rock's back playfield is definitely a tilemap, it's 160 tiles wide. Quite a few of your guesses about how this game works are way off the mark, and with WinUAE it's pretty trivial to verify things.
Another thing you have overlooked in your earlier posts is when you suggested you don't need to save the graphics behind the baddies as you can just restore them from the tiles. This only works if you are going to redraw every enemy each update, which in some games is extremely wasteful.
Consider the situation of a background tilemap, with 10 enemies that hardly move/animate, and say a bullet (with higher priority) passing over them. If you restore from tiles, you have to restore the background, then paste down the enemies, then the new bullet, when really only the graphics behind the bullet need to be replaced.
Also the tile method can be extremely wasteful. If you have a small bullet (say 8 pixels wide by 2 high), that could potentially be covering 4 different tiles (and doesn't Mr Beanbag use massive 32x32 tiles?). That's a hell of a lot of blitter use just to move a tiny bullet.