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RenderMan’s RIS is a rendering mode designed for efficient global illumination. You can use this mode by turning on the RIS Mode checkbox on the RenderMan node.
This rendering mode utilizes BxDF shaders, which are implemented as C++ plugins. They are represented in Houdini as digital asset nodes that can be placed inside the RIS shading network. In addition to BxDF shaders, which are assigned to geometry (much like surface shaders), there are also integrator shaders that can be referenced in the Integrator parameter of the RenderMan node. There are also various pattern and utility shaders that serve as inputs to the BxDF shaders for dynamic calculation of the main shader parameters, and to create shading groups and layers.
In addition to RIS shaders, the RIS shading network also allows OSL shaders. The OSL shader can be defined with an OSL shader node or, if it’s compiled as
.oso file, with a digital asset, similar to RIS shaders.
The only difference is the Render Mask that should be set to
OSL for OSL shaders (and
RIB for RIS shaders). OSL shaders are used the same way as RIS pattern shaders.
Define a new BxDF, integrator, or a pattern shader node for a corresponding custom C++ plugin
Create an OSL shader