Reference/Release Notes/3.5/Cycles

= Cycles =

Light Sampling
Cycles now uses a light tree to more effectively sample scenes with many lights. This can significantly reduce noise, at the cost of a somewhat longer render time per sample.


 * Light tree sampling is enabled by default in new scenes. It can be disabled in the Sampling > Lights panel.
 * If the light tree yields different render results, the most likely cause is light clamping. Clamping is a biased method that depends on the sampling strategy. Generally if the light tree works well, there will be less clamping and the render will be closer to the unbiased result.
 * The light tree works best in scenes with physically correct lighting, that is no custom falloff or ray visibility tricks. These may interfere with heuristics used in the light tree.
 * Materials with emission now have a new Emission Sampling setting, replacing the previous Multiple Importance Sample toggle. Auto is the new default, and uses a heuristic to estimate the emitted light intensity to determine of the mesh should be considered as a light for sampling. For single sided emitters or closed meshes, setting this to Front faces only can reduce noise with the light tree.

NOTE: the light tree is currently disabled for AMD HIP GPU rendering. We plan to resolve this before the final release.

Open Shading Language
OSL can now be used with OptiX on the GPU, in addition to existing support with CPU rendering.

There are some limitations currently, namely that texture lookups all use default filtering, not all noise functions are fully implemented and one cannot trace additional rays from OSL (as such the AO and Bevel nodes do not work either).

Changes

 * Improved adaptive sampling for overexposed scenes, reducing render time by taking into account absolute light intensity. This can negatively affect some scenes where compositing or color management are used to make the scene much darker or lighter. For best results adjust the Film > Exposure setting to bring the intensity into a good range, and then do further compositing and color management on top of that. Note that this setting is not the same as Color Management > Exposure.

Bug Fixes

 * Fix Anisotropic BSDF with Beckmann roughness using isotropic sampling