Bit shifts processing tile flips break down around gid=>2^28

[pgainullin]

See this example including sample data:

https://gist.github.com/pgainullin/bdf8ac141e9501958c993bb4467685fb

Running it in DartPad shows several IDs turn to 268435492 and 268435498 post flag-clearing. Given that there are bit shifts in this code and 2^28=268435456 it looks like some sort of an overflow error.

I can't see any issues just by looking at the code in tiled/src/layer.dart assempleTileMatrix vs the docs (https://doc.mapeditor.org/en/stable/reference/tmx-map-format/) but I don't know enough about bitwise operations in Dart to really understand it

[luanpotter]

This is an issue with the underlying https://github.com/flame-engine/tiled.dart/ library, not with flame_tiled. I will link this issue there, and close this one.

[luanpotter]

Bringing this from the old flame_tiled repo

[natebot13]

The root issue is from this section of the tiled documentation: https://doc.mapeditor.org/en/stable/reference/global-tile-ids/#gid-tile-flipping
The tile data probably comes from a hexagonal map, meaning the 29th bit is on, but tiled.dart only handles orthogonal maps, and only clears the top 3 bits. It should clear the top 4, and possibly even save the status of the bit into a new Flips flag in case a user wants to parse a hexagonal map.