"You can scroll around the whole Dragon Quest 1 map smoothly. Diagonals are a little jittery because Petit Computer is not fast enough to draw both a horizontal and vertical row of tiles in the same frame. It wouldn't be a problem if I split up the horizontal/vertical drawing between two frames but this is just a demo. :)
DQ1 Scrolling Map Demo QR Codes
As it says on the pic, the program draws new tiles just off screen when it needs to scroll in that direction. If you're moving to the right, it draws the next column to the right. If you're moving downward, it draws the next row downward. When drawing columns it actually draws one extra tile on the top and bottom so it takes care of the corner tile when moving diagonally.
Took a lot of messing around but it's satisfying. I could add some more user-defined variables and make it very adaptable for any type of map array, usable in platformers etc."