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Light filters implement the RixLightFilter interface found in RixLightFilter.h.  A light filter must implement three methods: the five methods of the RixShadingPlugin interface, Init(), Finalize(), GetParamTable(), Synchronize() and CreateInstanceData(), and the three methods of the RixLightFilter interface, Filter(), GetProperty(), and GetRadianceModifier().

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Like bxdfs, light filters can be parameters to other light filters. The last filter given before an AreaLightSource call an Light call (the root filter in a tree of filters) is responsible for delegating to the filters in its parameter list. Furthermore, light filters can be disabled on a gprim basis. To respect this, it is the responsibility of the filter to call RixLightFilterContext::IsEnabled(). If the upstream filter is not enabled, don't run it. IsEnabled() also returns a pointer to the upstream filter's instanceData, which should be passed to its Filter() method.

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