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Master Attributes are typically the heavyweight geometric data that is best shared for efficiency reasons, like normals, vertices, etc. Note that these attributes can only be used on the Master object. You can find these listed here.

Instance Attributes

Instance Attributes allow for variation and more for multiple different instances and are only available to instances, not the master. Things like bxdf assignment, light linking, trace sets, and more can be assigned per-instance. You can find this list here.

Tessellation

RenderMan tessellates geometry using an adaptive technique such that the resulting micropolygons have a length measured in a small number of pixels. This is typically the instance closest to the camera. However, this technique is not useful because with this screen projection based technique, no single tessellation can be reused for an object master instanced at different distances from the camera. Instead, the default tessellation is a world distance based measurement: the micropolygon length is measured directly in the units used in the scene, without projecting to the camera.

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By default, RenderMan attempts to flatten instances to improve performance and allow for more options when applying variation. However, there are times when this might not be desired. Large scenes, like a forest scene, may have worse performance when flattened especially when it comes to memory usage. Flattened instances multiply when nested, i.e. 1,000 instances of 1,000 instances becomes 1,000,000 instances. Nested instances add, i.e. 1,000 instances of 1,000 instances is 2,000 instances. As such we have an option to manually disable this behavior by choosing Nested Instancing exposed in the bridge products.

Attributes like trace sets and visibility cannot be altered when using Nested instances. This is the current trade-off for the improved memory usagethat are not supported when nested are:

• Lighting Subsets and Exclude (light linking)
• Lightfilter Subsets
• Visibility Flags (camera, indirect, transmission visibility, etc)

Note that they will inherit the properties of the parent instance, procedural, or archive.

There is an internal limit on nested instances, after 4 levels/parents, after this limit we automatically flatten the hierarchy.

Shading Variation

Even though the driving factor behind instancing is to minimize the variability between copies in order to maximize reuse and save memory, it is often still very desirable to be able to shade each variant differently. RenderMan supports shading variation primarily by the following methods:

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