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Light filters implement the RixLightFilter interface found in RixLightFilter.h.  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(), and CreateInstanceData().    Additionally, your light filter subclass must implement the three methods of the RixLightFilter interface, Filter(), GetProperty(), and GetRadianceModifier().

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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RixLightFilter::Filter()

Filter is where the work is done.

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for(int j = 0; j < contribution->GetNumSpecularLobes(); ++j) {
    for(int i = 0; i < numSamples; ++i) {
       contribution->GetSpecularLobe(j)[i] *= RtColorRGB(1.0,0.0f,0.0f);
    }
}

for(int j = 0; j < contribution->GetNumDiffuseLobes(); ++j) {
    for(int i = 0; i < numSamples; ++i) {
       contribution->GetDiffuseLobe(j)[i] *= RtColorRGB(1.0,0.0f,0.0f);
    }
}

RixLightFilter::GetProperty()

RixSCDetail PxrGobo::GetProperty(
    RtConstPointer instanceData, LightFilterProperty property, void const** result) const
{
    myData* data = (myData*)instanceData;

    if (RixLightFilter::k_LinkingGroups == property)
    {
        (*result) = &data->m_linkingGroups;
        return k_RixSCUniform;
    }
    return k_RixSCInvalidDetail;
}

RixLightFilter::GetRadianceModifier()

bool PxrMyLightFilter::GetRadianceModifier(
    FilterRadianceModifierProperty property,
    RixLightFilterContext const* lfCtx,
    RtConstPointer instanceData,
    float* result) const
{
    *result = m_attenuation;
    return true;
}

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