Cycles: removed UV requirement for MNEE, along with fixes and cleanups

Remove need for shadow caustic caster geometry to have a UV layout. UVs were
useful to maintain a consistent tangent frame across the surface while
performing the walk. A consistent tangent frame is necessary for rough
surfaces where a normal offset encodes the sampled h, which should point
towards the same direction across the mesh.

In order to get a continuous surface parametrization without UVs, the
technique described in this paper was implemented:

"The Natural-Constraint Representation of the Path Space for Efficient
 Light Transport Simulation" (Supplementary Material), SIGGRAPH 2014.

In addition to implementing this feature:
* Shadow caustic casters without smooth normals are now ignored (triggered
  some refactoring and cleaning).
* Hit point calculation was refactored using existing utils functions,
  simplifying the code.
* The max number of solver iterations was reduced to 32, a solution is
  usually found by then.
* Added generalized geometry term clamping (transfer matrix calculation can
  sometimes get unstable).
* Add stop condition to Newton solver for more consistent CPU and GPU result.
* Add support for multi scatter GGX refraction.

Fixes T96990, T96991

Ref T94120

Differential Revision: https://developer.blender.org/D14623

0 files changed, 0 insertions, 0 deletions