N and W and NW tiles only
To create perpendicular wall maps, I need only N and W wall tiles, plus a NW one. N and W defines one edge each. NW defines two edges.
Then there’s the block tile, which is impassable.
S and E seemed superfluous.
Shadows and lights
Now, there’s an issue with possible spillover from the tile boundaries, for example, when some AO/shadow or lights are rendered.
Shadows on floor won’t appear on top of walls at any time, so they can be placed in a shadow layer below the walls. Lights on floor is the same thing (lights on walls, is another issue).
Generate at runtime
These floor-level effects are objects because the effect spills over to other tile spaces, and so they can placed by hand. Or, procedurally: tagging tiles with ‘floorlights’ sprites (as C2 objects) can be generated at runtime.
Shadows and lights on walls is problematic because they need to be associated with the walls, which means they follow the z-ordering.
Maybe I can ‘parent’ the z-order during creation phase (association phase). Then I need to figure out how to exclude sorting for those in ZSorter.