Autotiling & Edge Transitions

Overview

Hard edges between grass and water look like a checkerboard. Autotiling picks the correct edge/corner transition tile based on a bitmask of neighbors. This skill defines the transition set and the bitmask rule.

When to Use

• Two terrain types meet and the seam looks harsh.
• You want maps to look hand-blended without hand-placing every edge.
• You need a repeatable rule for which transition tile to use.

Process

1. Define the base terrains and their priority order (e.g. water < sand < grass).
2. Author the 16-tile (or 47-tile) transition set for each terrain pair.
3. For each cell, compute a neighbor bitmask (N, E, S, W and corners).
4. Map the bitmask to the correct transition tile index.
5. Render the transition tile on top of the lower-priority base.
6. Verify all 16 bitmask cases visually with a test map.
7. Cache the bitmask->tile lookup for performance.

bitmask = N*1 + E*2 + S*4 + W*8  ->  transitionTile[bitmask]

Rationalizations (Stop Lying to Yourself)

Excuse	Reality
"I will hand-place edge tiles"	Hundreds of edges by hand is unmaintainable. Use a bitmask rule.
"One generic edge tile is enough"	Corners need their own tiles or you get gaps. Author the full set.

Red Flags - STOP if you catch yourself:

• Hard checkerboard seams between terrains.
• Missing corner transition tiles.
• Bitmask computed but never cached (slow).

Verification

You are NOT done until every box is checked:

• A complete transition set exists per terrain pair.
• All bitmask cases render correctly on a test map.
• The bitmask->tile lookup is cached.