Box Drawing Characters + Marching Squares = Marching Boxes?

I couldn't figure out the name of this to search for it online, and it wasn't mentioned on Wikipedia's marching squares page, so… here's to reinventing wheels ( :

Sebastian Blomfield's "Lord of the Manor" game inspired me to explore retro-game engine coding. So far, I've got a basic tile-shader that renders tiled 2D game environments (e.g. game of life, forest fire simulation). Next up: what if I want to draw maps where the adjacent tiles of e.g. walls are continuous?

Box-drawing characters are a nice way to generate rectilinear paths in a tile-based game environment. By checking whether the tiles above/below/left/right are also walls, we can select one of 16 box drawing symbols to create continuous walls:

Note that this extends the usual unicode box-drawing characters with five additional tiles: one for an isolated (disconnected) wall, and four for "dead ends". These suffice for rendering square hallways, e.g:

With some tweaks to the tiles, we can coax box-drawing tiles to generate more curved and diagonal paths:

See here for an example page that renders dendriform growth using the above tile sets (refresh to get a new randomly-selected tile set).

Marching squares is another nice algorithm for rounding off corners on a map (e.g.). This doesn't quite work out-of-the-box for our tile shader, however, since marching squares accepts the values for the corners of each tile, and I want it to operate on the tile values directly. It also uses 16 tiles:

So! box-drawing is good for lines, and marching squares is good for borders/contours. Can we combine these and get a best-of-both-worlds approach? One that renders tiles based on their current value and the values of their neighbors?

Yes. I'm not sure what its name is, so I'm calling it "marching boxes" for now. Marching-boxes extends the box-drawing tiles with 31 tiles (below). These provide versions of the corner, T-junction, and cross-junction tiles that account for the possibility of nearby filled-in regions. The resulting tiles can render contours around filled-in regions as well as sharp lines.

Including background and foreground tiles, marching boxes uses 48 tiles.

This could be nice for any pattern that has a mixture of lines and enclosed regions, like a dungeon connected by hallways, or a water system that includes both lakes and rivers.

Click here to view a WebGL demo of marching-boxes tile rendering