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Will turn on all light filters in group "blockers" for all lights shining on the sphere.  By convention, all of the filters shipped with RenderMan use "linkingGroups" as the name of the parameter.   Both the "linkingGroups" and "lightfilter:subset" strings may be comma-separated lists of group names.  Group name matching is not scoped to a light.  Any filter in a matching group on any light active on a given geometric primitive will be enabled.

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Implementing the RixLightFilter interface

Light filters implement the RixLightFilter interface found in RixLightFilter.h.  A light filter must implement the five methods of the RixShadingPlugin interface, .  RixLightFilter is a subclass of RixShadingPlugin, and therefore shares the same initialization, synchronization, and parameter table logic as other shading plugins.  Therefore to start developing your ownlLight filter, you can #include "RixLightFilter.h" and make sure your light filter class implements the required methods inherited from the RixShadingPlugin interface: Init(), Finalize(), Synchronize(), GetParamTable(), Synchronize() and CreateInstanceData(), and the three and CreateInstanceData().  Generally, there is one shading plugin instance of a RixLightFilter per bound RiLightFilter (RIB) request. This instance may be active in multiple threads simultaneously.  Additionally, your light filter subclass must implement the three methods of the RixLightFilter interface, Filter(), GetProperty(), and GetRadianceModifier().

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