posted on www.fourisland.com How Frog Game Allows You To Modify Map Data
It might look like two trees, but it's actually one. The borders of a top-down map are the same logical space as the borders in the adjacent maps, so those two trees actually represent the same object. It would be a finnicky edge case for the game to have to write two terrain edits to memory specifically when this tree gets destroyed. Instead, both trees are assigned the same global coordinates:
- Left tree is on map (14, 2) at tile (9, 3). Global coordinates are (14 * 9 + 9, 2 * 7 + 3) = (135, 17).
- Right tree is on map (15, 2) at tile (0, 3). Global coordinates are (15 * 9 + 0, 2 * 7 + 3) = (135, 17).
Hatkirby has been writing a very intriguing series of posts on reverse-engineering For Frog the Bell Tolls, a lovely and underappreciated gem of the Game Boy's library. This is actually just the most recent post; you can read the whole series here (start at the bottom and work your way up). This has a lot in common with my own currently-on-hold reverse engineering projects, and it's interesting to see a lot of the same problems tackled for a very different piece of software with very different tools for working with it.