Disco teapots, rendered using the PxrVCM integrator.

Integrators take the camera rays from the projection and return shaded results to the renderer. For the main integrators these are estimates of the radiance from the surfaces seen from the outside along the rays. These main integrators are responsible for computing the overall light transport. Interior integrators assist in specialized cases by handling the light within surfaces or volumes. We provide two main production quality integrators, though users can substitute their own.

PxrPathTracer implements a unidirectional path tracer. This combines information from the materials at the hit points with light samples to estimate direct lighting and shadowing, then spawns additional rays to handle indirect lighting. This works well with environment lights, and large direct light sources.

PxrVCM extends this with bidirectional path tracing. In addition to the paths from the camera, it traces paths from the light sources and tries to connect them. It can resolve complicated indirect paths that may be slow to converge with PxrPathTracer. In particular, it is designed to handle specular caustics.


RPS 19 includes example RIB files and shaders demonstrating the integrators, at the heart of the RIS rendering mode. These examples can be found in the /lib/examples/RIS/scenes directory of your RenderMan Pro Server installation, in the /spt and /vcm subdirectories. Some of the examples are discussed in detail in the pages below. Whether or not you're inclined to open up a terminal window and render along, these pages serve as a broad overview of the features and capabilities of PRMan's RIS mode.

images/sohoCrop.png Soho - a teapot and emissive geometry in a volume, with reflections all around, this scene demonstrates improved volume sampling capabilities in a complicated lighting scenario. This example uses the PxrPathTracer integrator.
images/skullsCrop.png Skulls - This example demonstrates the ability of the PxrVCM integrator to resolve complex light paths, in particular the specular-diffuse-specular that arise from reflections or refractions of caustics.

The distribution also includes the following integrators, provided for debugging and reference purposes: