This is something I am wondering about as well. Having a thing to be able to exclude specific actors would be awesome.
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Well I'll see what I can do with gameplay tags since that's a good idea. But first, I need to finish functionality related to custom depth and stencil.
I think the new update is more than halfway done, so it will include expanded functionality for excluding objects.
I've found a proper way to read Stencil values of objects for operations within the shader, but I still need to find a more optimal way to pass this values and work with this array inside the shader code (which is always tricky with arrays in HLSL).