The core of the issue is that there are backfacing interpolated normals, NdotL and/or NdotV end up being negative for them.
Things we tried:
1. Explicitly using geometry normals for some things. Doesn't really work that well.
2. Clamping NdotX to some small value instead of just ignoring light contribution. Works better, but there are still some artifacts.
1. Probabilistically let ray through material or reflect it based on
transparency probability (which is essentially just alpha for now).
2. Introduce opaque flag to be able to treat transparent objects as not
casting shadows. This is not very realistic, but oh well.
this is mostly copied from ray tracing gems 2 chapter 7 (Texture Coordinate Gradients Estimation for Ray Cones, by Wessam Bahnassi).
There's a weird bit about radians vs degrees. We'll figure it out later when the book becomes available.
this is very proof-of-concept quality. it should be definitely done some other way
e.g. we should control reflectivity and transparency differently (and not together)
and they should be based on texture ids, not on render_mode
it's also unfortunate that transparency required a lot of bounces. we should probably control transparency bounces separately from light bounces.
alternatively, transparency effects (beams, sprites) should be done with custom intersection shaders and not based on transparent geometry
