RMS 18

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    RMS: Occlusion AOV


Because occlusion does not take lighting in account it cannot be considered to be a physically plausible shading technique. Nonetheless, RMS 18 (and higher) does support the rendering of basic (ambient) occlusion. This tutorial shows how occlusion is rendered - figure 1.

Figure 1

Step 1 - Add Occlusion Controls

Note: this step is best down BEFORE any other RMSxxx materials have been applied to the surfaces in a scene. If the scene have already been assigned a variety of RMSxxx materials refer to Alternate Step 1.

In the Render Setting->RenderMan->Features panel make sure "Ray Tracing" is active.
1.1     Select all the surfaces in the scene and assign them RMSMatte.
1.2     Lower "Surface Color" of RMSMatte to black.
1.3     Click the connection icon of "Incandescence".
1.4     Connect "Incandescence" to a rmanOcclusion node (figure 2).

Figure 2

Step 2 - Controlling the Quality of the Occlusion

To improved the quality of the caustics increase the "Samples" - figure 3.

Figure 3

Alternate Step 1 - Add Occlusion Controls

The alternative procedure shown next will allow any RMSxxx materials that are already assigned to the surfaces in a scene to be non-destructively replaced by a shared instace of RMSMatte material to which it's "Incandescence" slot has been connected to "rmanOcclusion".

Use the RenderMan->Dynamcic Rules menu open the Rules panel - figure 4.

Figure 4

1.1     Click the "Add Rule" button.
1.2     Double click the "XPath" field and enter "//*".

1.3     Right click on the "Empty" payload and choose "Insert Payload".

1.4     Choose the version of RMSMatte that has the rmanOcclusion connection.

When the scene is rendered the RMSMatte will be used to render the occlusion. However, when the rule is removed subsequent renderes will continue to use the the existing RMSxxx materials.

For more information about XPath's refer to the Pixar document "Dynamic Rules".

© 2002- Malcolm Kesson. All rights reserved.