3x3 Auto Tile demonstration

This little project is intended to demonstrate that diagonal connectivity is possible on a 3x3 autotile without requiring both the side tiles adjacent to the corner, and hopefully provide evidence supporting the inclusion of this autotile mode in godot 4.0 tilemap functionality.

 A 16x16 grid is generated displaying results for each of the 256 unique neighbor combinations. Neighbors are masked out to highlight the tile chosen for the neighbor combination, and an overlay of the autotile bitmap for the selected tile is shown with red indicating required neighbors, and cyan indicating don't care neighbors.

There are two sample TileSets.  

The first (green mountains) uses simple hand drawn artwork to clearly show continuity between adjacent tiles. This TileSet is comprised of approximately 160 unique 64x64 pixel tiles for use on a 64px grid. Diagonal connectivity with this tile set does require "at least" one adjacent side be active, but many tiles have diagonal connectivity with only one side and not both. This is done by ensuring the continuous edge line for these tiles passes through the inside of the corners.
Non connecting diagonals are  configured with "Don't Care" bits set.

The second (brown road) uses tiles generated by the tool TilePipe2. It achieves smooth diagonal connectivity in a different manner. by generating tiles larger than the target grid so that they overlap and are generated so that the overlapping areas are either transparent, or are guaranteed to be identical to the neighbor (so it doesn't matter which ends up on top. 
In the example provided the tiles are 48x48 for use on a 32x32 grid.  The mask used for this set shows the entire tile with a smaller square indicating the bounds of the grid cell the tile is set upon. Here you can find several Y and X patterns that consist of exactly 4 or 5 tiles joined at diagonals with the side neighbors empty.

Controls:

up/down/left/right can be used to navigate the grid.

"accept" (enter) can be used to adjust the opacity of the neighbor mask.

"select" (space) to switch between tile sets

"cancel" (escape) can be used to hide/show the auto tile bitmap.