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The usual workflow for aggregate volumes is to create a named aggregate volume by attaching the Attribute "volume" "string volumeAggregateaggregate" ["name"] to one or more RiVolumes primitives, where "name" is the desired name of the aggregate volume. These volume primitives should use the PxrVolume shader to control their volumetric appearance. Once several volume primitives have been tagged with this attribute with the same name, the named aggregate volume can be supplied as the "volumeAggregate" parameter to the PxrPathTracer integrator. This signifies that the global volume aggregate for the scene is the named aggregate volume. The named volume aggregate will now appear in renders. Control over how the volume is integrated and sampled is via parameters on the PxrPathTracer integrator.

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Mipmapping is a standard technique used to improve texture aliasing and rendering performance by automatically choosing an appropriate texture resolution level from a pyramid based on viewing size and angle of the texture on screen. This technique can also optionally be applied to volumetric data comprised of voxels: in much the same way that a 2D mipmap pyramid level contains texels that are averages of four finer texels, a 3D mipmap pyramid level contains voxels that are each averaged from eight finer voxels. Mipmapping a volume asset will increase its disk space significantly, and may increase memory during rendering somewhat if the finest voxels are appropriately sized to the level of detail required for the camera; however, if the voxels are much finer in detail than the camera settings require, mipmapping can save significant RAM and render time because the renderer will only load coarser averaged voxels instead. Aggregate volumes using the impl_openvdb plugin as a data source for the volume primitives can enable mipmapping by setting the filterWidth parameter to a value greater than 0; this parameter is a multiplier on the standard filterwidth computed by the renderer.

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