Iray Programmer's Manual

Caustic sampler

The Iray Photoreal caustic sampler can be used to improve the quality of caustics in typical turntable scenes. When enabled, Iray Photoreal will augment the default sampler with a dedicated caustic sampler, designed to improve capturing caustic effects. In terms of light path expressions, the caustic sampler was designed to handle paths with the signature E D .* S L much better.

The following attribute on the IOptions class, shown here with its default setting, controls the caustic sampler:

bool iray_caustic_sampler = false

Enables the caustic sampler if set to true.

The Iray Photoreal caustic sampler was mainly designed for typical turntable scenes (but is not limited to them). It thus performs best under the following conditions:

  • The scene geometry is (mostly) in view.

  • The caustics are (mostly) in view.

  • The scene is positioned on top of a groundplane or large surface.


To catch caustics on the groundplane, the groundplane environment_dome_ground_reflectivity must be set. See Environment dome and implicit groundplane for a description of the groundplane and its settings.

The caustic sampler will not improve caustics in all use cases, and thus can actually harm overall rendering performance. The caustic sampler can fail to improve caustics under the following conditions:

  • Only a small part of a larger scene is in view (e.g., the camera zooms in on a single item in a detailed scene).

  • The camera zooms in on a small part of a much larger caustic.

The caustic sampler can be used in combination with the Architectural sampler to help rendering caustics more efficiently in difficult scenes and lighting situations.

  • It is not always beneficial to enable both samplers at the same time as there is additional computational overhead involved that can outweigh the benefits.
  • The caustic sampler only improves on directly visible caustics. Caustics seen through mirrors or windows are currently not improved by the caustic sampler.