- Connect the Presence parameter to a texture that defines a "cut out" in the surface. For instance, we model a leaf as a cheap bilinear patch and paint a black and white mask for shape of the leaf.
- To hide particles.
- When you need to control the opacity of an object. Keep in mind the production integrators may have this feature off (set to 0) for efficiency reasons. You can enable this opacity calculation to a certain depth by making the 0 an integer with a reasonable low number.
When Not to Use
- Not for translucency, transparency, or refraction.
- Presence should be set to either 0 or 1. Setting presence between 0 and 1 will produce unwanted noise!!! For instance, if we set the presence to 0.4, we are telling the renderer that there is 40% chance of hitting the surface and 60% chance of missing the surface! This is illustrated in the example below:
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If we want to shade a translucent surface, we can set the Double Sided Transmit shading parameter under the DIffuse Diffuse controls of PxrSurface instead.