Cycles Volume Render

To Do

• Support BSDFs in volumes
  • Material density output (like displacement)
  • Gradient of density field = normal, compute like bump mapping

• Multiple scattering approximation with octaves
• Use ray differentials for volume shading

• Verify lamp MIS correctness with volumes and mix of surfaces and volumes.

• World volumes
  • Do we need an option to exclude the world volume from the interior of objects? Some more general mechanism?
  • Very low density should not be optimized out for closures, now there is a discontinuity.

• Incorrectly connected surface shader to volume socket: detect and ignore? (#39089)

• Random jitter offset for heterogeneous volumes can use stratified samples
• Add a user setting for transparency cutoff, as optimization and to make creating opaque volumes possible without infinite density.
• Ray visibility (partially there)