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The RixBxdfFactory interface defines is a subclass of RixShadingPlugin, and defines a shading plugin responsible for creating a RixBxdf object from a shading context (RixShadingContext) and the set of connected patterns (RixPattern).

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Integrators (RixIntegrator) use RixBxdfFactory objects by invoking RixBxdfFactory::BeginScatter()  to obtain a  RixBxdf. Because a RixBxdf is expected to be a lightweight object that may be created many times over the course of the render, RixBxdfFactory is expected to take advantage of the lightweight instancing services provided by RixShadingPlugin; in . In particular, BeginScatter() is provided a pointer to an instance data that is created by RixBxdfFactory::CreateInstanceData(), which is called only once per unique set of parameters supplied to the material description. It is expected that the instance data will point to a private cached representation of any expensive setup which depends on the parameters, and BeginScatter() will reuse this cached representation.

RixBxdfFactory::BeginScatter()  is expected to invoke  RixShadingContext::EvalParam() to invoke the relevant bxdf parameters. The bxdf acts as a closure, associated with a given shading context.  BeginScatter() will typically call a Bxdf constructor which will get the necessary built-in variables such as shading normal (Nn), geometric normal (Ngn), viewing direction (Vn), etc., by calling the RixShadingContext::GetBuiltinVar() function for each variable.

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