Chunkifying Details

When a Bundle is 'Chunkified' by the Layout/Chunking system the Bundle creates a cache of data in each TileBundle for rapid loading or re-loading of tiles using the TileChangeData and Tilemap.SetTiles(TileChangeData[] tileChangeDataArray, bool ignoreLockFlags).

When the layout system wants to fetch a chunk of tiles to load in this fashion it uses the Bundle's `GetCachedTcd(RectInt locator, out TileChangeData[]? tcd)' method.

For Unity tiles the cached data are directly copied into the output array. The array itself is an instance field of the Bundle.

For TPT tiles, these are new, fresh, clones of the archived, Locked, TPT tile assets which are sub-objects of the Bundle asset.

What this means is that every time that the chunk of tile data are retrieved in this fashion new, fresh TPT tilestile instances are created. Immediately after SetTiles is used the instance array is cleared.

Why do this??

Since each TPT tile is an independent instance, once it's loaded to a Tilemap its internal state may change during the time it's actually in the Tilemap; i.e., until it's unloaded. Hence, we really don't want to re-used these modified tiles once they're unloaded.

If these were unloaded and re-loaded later then the modified fields will still be modified, which can cause all sort of bizarre errors that would be hard to troubleshoot. Obviously you'd like an unmodified clone of the corresponding locked tile in the Bundle asset.

The end result here is that the TPT instance which gets loaded to the Tilemap has no references anywhere else. That way, when the tile is eventually unloaded it becomes garbage collected properly rather than be a potential memory leak.