Iray Programmer's Manual

Limitations

Result Canvases

Iray Photoreal supports all Canvas names in render targets with the following limitations:

  • Iray Photoreal can currently render up to 20 light transport canvases at once. Light transport canvases are result, irradiance, and irradiance_probe canvases, including either built-in LPEs like diffuse or user-defined LPEs. Additional light transport canvases raise a warning and will be ignored. This limitation does not apply to other canvases like object_id or normal, which may still be computed in addition to this limit.

  • The number of texture spaces available through texture_coordinate[ n ] is currently limited to four.

  • The irradiance canvas cannot be used in the same render call with any of the result render buffers.

  • The irradiance_probe canvas cannot be used in the same render call with any other canvas.

  • The irradiance_probe canvas cannot be used with the caustic sampler.

  • Iray Photoreal cannot render the shadow canvas.

  • Iray Photoreal cannot render the ambient_occlusion canvas. Note that the full effect of geometric occlusion on illumination is of course included in the global illumination of Iray Photoreal.

Light Path Expressions

Iray Photoreal supports all light path expressions, with the following limitations:

  • EDF specifications are not supported and will raise an error message.

Materials

Iray Photoreal has the following limitations on its material model, which is based on the Material Definition Language (MDL):

  • The number of elemental BDSFs per material are currently restricted to a maximum of 16.

  • The number of (procedural) texture functions per material are restricted to a maximum of currently 32.

  • Spectral dispersion resulting from a spectral index of refraction (e.g. specified by using base::abbe_number_ior) is currently only supported for df::specular_bsdf and not for df::simple_glossy_bsdf.

  • The material's volume scattering coefficient is a color in MDL, however, Iray Photoreal only supports a scalar scattering coefficient and hence uses the luminance of that color for this.

Decals

Iray Photoreal has the following limitations on decals:

  • The number of decals whose clip box can overlap at a surface shading point is limited to six. If a decal is applied on both sides of a surface, it naturally counts twice towards this limit. The number of decals in general is unlimited.

Section Planes

The maximum number of planes in Iray Photoreal is currently limited to eight.

Rendering

Iray Photoreal does not support volumetric effects beyond subsurface scattering. Iray Photoreal ignores the attributes reflection_cast, reflection_recv, refraction_cast, refraction_recv, shadow_cast, and shadow_recv.

Picking

Picking can only be used on a render context that has already been used at least once to render. Otherwise picking will return with a proper diagnostic and not pick any object.

Picking reports only the first hit as a result.