Reference/Release Notes/3.4/Cycles


Path Guiding

Path guiding was integrated (75a6d3abf7) into Cycles using Intel's Open Path Guiding Library.

This feature improves the sampling quality of individual paths reducing the noise in complex lighting scenarios such as; long indirect light bounces, indirectly illuminated shadow areas, or reflected light sources.

Note: While Path Guiding helps to render scenes containing simple caustics (e.g., water surface), it is not designed to be a caustic solver, such as MNEE, meaning it might not help render scenes containing complex caustics.

During rendering, path guiding learns an approximation of the scene's light distribution (direct and indirect). This information is then used to guide paths into important directions that might not be explored well using standard directional sampling methods that only consider the local material or the directly visible light sources.

More details about path guiding, how it works, and how it is integrated into Cycles are presented in the BCON2022 talk Follow the light: introducing path guiding in Cycles.

At the moment, path guiding is only available for CPU rendering and can be enabled in the render properties panel under ‘Sampling->Path Guiding’. The current implementation supports guiding on surfaces with diffuse BSDFs components as well as inside volumes.

The following images show the effects of path guiding in practice when applied in different scenes with complex lighting scenarios. Each comparison is rendered at an equal time.

Equal time render without and with path guiding, original scene by Andy Goralczyk
Cycles path guiding 0 before.png
Cycles path guiding 0 after.png
Equal time render without and with path guiding, scene by Alaska
Cycles path guiding 1 before.jpeg
Cycles path guiding 1 after.jpg
Equal time render without and with path guiding, scene by Jesus Sandoval
Cycles path guiding 2 before.jpg
Cycles path guiding 2 after.jpg


  • Attribute node: support for using attributes of geometry nodes instances. Additionally, boolean and integer array attributes can be read from objects. (2f7234d3e1, 554afabf75)
  • Attribute node: new View Layer mode for accessing attributes of the current View Layer, Scene or World (f61ff22967)
  • Baking: new option to bake specular effects from the active camera view, instead of above the surface. This may be useful when baking textures that will be viewed from a fixed position or with limited camera motion. (b475506b47)
  • Sampling: improved patterns to reduce noise in some scenes, particularly for volumes and long area lights. (50df9ca50d, a06c9b5a06)

GPU Rendering

    • AMD Radeon RX 7000 series graphics cards (RDNA3 architecture) now supported.
    • On Linux, upgrade to ROCm 5.3 or newer to fix issues with textures on Vega and RDNA1 graphics cards.
  • Apple Metal
    • Shadow caustics enabled.
    • Intel GPUs now supported starting with macOS 13.
  • Intel OneAPI
    • Upgrade to driver version 101.3430 or newer to fix user interface crashes.

Open Shading Language

Open Shading Language was upgraded to version 1.12.6.

This comes with change in behavior for input parameters with a non-constant initializer. For such parameters, the input socket on the node now shows no editable value, it can only be linked. This can also be specified through metadata.

shader test(
  normal Normal = N,                           /* Value hidden due to initializer. */
  float A = 0.0 [[ string widget = "null" ]])  /* Value hidden through metadata. */