Multiplane AR Shadows

[hillesland]

The shadowMultiplier trick seems to work well for multiple objects and a single "AR plane" (real-world planes picked put by AR tracking). But I'm looking for something that will work for multiple planes, and wondering if I'm missing an option to do it.

If i have two "shadowMultiplier" planes overlapping in light space, I end up with a shadow on both planes (not marked as shadow casters).

There are lots of hassles with AR planes and shadows (bad edges that change over time, shouldn't shadow cast on other AR planes) so I think a common solution is to just make per-object shadow images and attach them. I haven't dug far into whether I can do that with Filament though, without modification.

I could do a "collapse all vertices to y = plane and set color to (0, 0, 0, alpha)" thing, but it's not clear I've got the right tools for that (e.g., blend mode or stencil or whatever to resolve overlapping polys). allpha=1 isn't going to be an option.

There are various hacks possible with access to the shadow map in a material, but I'm not seeing that either.