Scenes and Shaders

To get started, you'll want to open the appropriate file for the recipes.
(Where are the Maya files?)

Open the scene, /scenes/recipes/area_light.ma.

In this scene an area light is set up to cast soft shadows. The shadows are ray traced and the area light has RenderMan Attributes attached to it to control how many ray samples the area light casts. More samples provide a higher quality shadow. This scene uses 256 samples to cast an artifact-free shadow.

Area light with 256 ray traced shadow samples

RECIPE #2: INTERIOR OCCLUSION

Open the scene, /scenes/recipes/interior_occlusion.ma.

In this scene we have our dragon in a box, with a simple Lambert attached to all the surfaces. The lighting is courtesy of a RenderMan Environment Light node. Straight out of the box, the defaults have the Max Dist parameter set to 10000, which, as you can see, doesn't get the job done:

Max Dist = 10000

For global illumination to work properly with interior scenes, you need to shorten the maximum distance that rays are shot to compute occlusion, meaning that you need to stop well short of your ceiling, or your scene will be fully occluded. In general, a good guideline for setting the Max Dist parameter is one-tenth the distance from your ground plane to your ceiling. In this scene, the ceiling is about 20 units from the ground plane, so we have set the Max Dist to 2.0, and, as you can see, we get a much more useful result:

Max Dist = 2.0

RECIPE #3: “PURE” OCCLUSION

Open the scene, /scenes/recipes/pure_occlusion.ma.

This scene outlines two ways to get a “pure” occlusion image, as seen in the Global Illumination tutorial. The “correct” way to get this so-called pure occlusion is to create an additional, secondary output for occlusion, via the Passes tab of the Render Globals, as we have done here. This output, however, is the actual occlusion data, as read and used by the renderer, and is the inverse of what you might expect to see:

Actual “pure” occlusion

You can, however, then invert that image with the tool of your choice, such as fCheck, which would give you this image, suitable for compositing:

Inverted occlusion

Or, you can “fake it” by using a simple Lambert shader with the color set to white and the diffuse value cranked to 1, giving you the following image in your Final rendered image:

Faked “pure” occlusion

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