Support fill-extrusion stroke style

[stevage]

It would be useful to be able to style the edges of fill-extrusions. (And possible, independently style the vertical edges versus the flat edges at the top and bottom).

Why? It's currently not possible to visually distinguish between two adjacent fill-extrusions. The main workaround is to give each of them a slightly different color (which means you can't really use color as an independent variable visualisation).

A contrasting stroke colour could also be aesthetically preferable in some cases, and to help better perceive the 3D shape. For instance:

I'm not fussed whether the occluded edges are rendered or not.

[lbud]

@stevage this property was initially implemented but removed due to concerns about antialiasing, as well as the lesson we'd already learned regretting fill-outline-color: mapbox/mapbox-gl-style-spec#456 (comment), #3223 (comment). We do not intend to revive it. To distinguish between extrusions I'd suggest experimenting with adding more contrast between your basemap and fill-extrusions and/or playing with the light property.

[stevage]

Ah, thanks. Dang. Seems like the kind of feature where for some use cases it would be worth someone forking the codebase to reinstate. That screenshot looks so sweet :/

[rowanwins]

Just dropping a note here that this is available in the ArcGIS JS API, eg this demo.

In my case I'd love to be able to render outlines to show the floors of a building and then apply symbology to each floor, for example looking at a building I can distinguish which floors have vacancy - this would have lots of potential in the real estate world for example.