Wondering how Embree determines which faces are 'backfacing' when this option is enabled upon compilation or set for a geometry.
Do all triangles in the surface need to be backfacing for the surface to be ignored by the ray? Or only the ones which would typically be hit by the ray?
A simple example being a ray passing through the barrel of a cylinder with some triangle normals facing the ray and others not.
Triangles whose geometry normal are pointing towards the ray are font faceing, the others backfacing. Backfacing triangle hits are ignored per ray if the RTC_BACKFACE_CULLING feature is enabled. In case of your cylinder only the front facing triangles would get hit by the ray.