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PxrVCM enforces multiple scattering in volumes; bidirectional path tracing in particular is well suited for multiple scattering in volumes. However, PxrVCM does not currently support volumetric photons; as a result, effects such as volumetric caustics may be slow to converge. For these effects you should use the PxrUPBP integrator with homogeneous volumes (heterogeneous volumes are not currently supported in PxrUPBP).

There are several important differences to note between this integrator and PxrPathTracer:

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