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The default tessellation of instanced objects bears special consideration in RenderMan. By default, RenderMan tessellates geometry using an adaptive technique such that the resulting micropolygons have a length measured in a small number of pixels. For instances, 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. This allows the renderer to reuse tessellations, but does require that the user specify this length directly (the default length is essentially unbounded, meaning that the geometry will be rendered at the coarsest possible representation - for subdivision surfaces, typically the control hull which may not be very detailed). In the pictures below, the teapot on the left is not instanced, while the teapot on the right is instanced with various settings of the world distance tessellation length. Carousel Image Slider
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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