Path tracing limitations

This section contains information on the limitations of HDRP's path tracing implementation. Mainly, this is a list of features that HDRP supports in its rasterized render pipeline, but not in its path-traced render pipeline.

Unsupported features of path tracing

Currently, you can only use HDR path tracing on platforms that use DX12.

HDRP path tracing in Unity currently has the following limitations:

  • If a Mesh in your scene has a Material assigned that does not have the HDRenderPipeline tag, the mesh will not appear in your scene. For more information, see Ray tracing and Meshes.
  • Path tracing in HDRP doesn't support the following:
    • 3D Text and TextMeshPro.
    • Shader Graph nodes that use derivatives (for example, a normal map that derives from a texture).
    • Shader Graphs that use Custom Interpolators.
    • Local Volumetric Fog.
    • Tessellation.
    • Translucent Opaque Materials.
    • Several of HDRP's Materials. This includes Eye, Hair, and Decal.
    • Per-pixel displacement (parallax occlusion mapping, height map, depth offset).
    • Emissive Decals.
    • Volumetric Clouds.
    • Water.
    • MSAA.
    • Graphics.DrawMesh or Graphics.RenderMesh, because rasterization and ray tracing are different ways of generating an image.
    • Streaming Virtual Texturing.

Unsupported shader graph nodes for path tracing

When building your custom shaders using shader graph, some nodes are incompatible with ray/path tracing. You need either to avoid using them or provide an alternative behavior using the ray tracing shader node. Here is the list of the incompatible nodes:

  • DDX, DDY, DDXY, NormalFromHeight and HDSceneColor nodes.
  • All the nodes under Inputs > Geometry (Position, View Direction, Normal, etc.) in View Space mode. Furthermore, Shader Graphs that use Custom Interpolators aren't supported in ray/path tracing.

Unsupported features of ray tracing

For information about unsupported features of ray tracing in general, see Ray tracing limitations.