In the Indirect Lighting tab of the Render Settings Window there is an Ambient Occlusion rollout that controls the global settings for creating ambient occlusion passes. These settings are bypassed when you activate the Use Local Settings in the Ambient Occlusion render pass attributes. Leave the Ambient Occlusion check box selected regardless of whether you are using local or global settings.
8. Maya 2011 now introduces local settings for tuning the look of the ambient occlusion pass. Scroll down to the lower section of the Attribute Editor, and activate the Use Local AO Settings feature.
9. The Rays attribute adjusts the overall quality of the ambient occlusion shading.
Increasing this setting improves quality but also increases render times. Leave this at 64, which is a good setting for testing.
Bright and dark colors The bright and dark colors determine how a surface is shaded based on the proximity of other surfaces or parts of the same surface. If you reverse these colors, you’ll see the negative image of the ambient occlusion shadowing. For most com- positions, it’s fine to leave these as black and white. The values can easily be edited in compositing software after rendering.
Spread Spread determines the distance of the shading effect across the surface. Think of this as the size of the shadow. Higher values produce tighter areas of shadowing on the surface; lower values produce broader, softer shadows.
Maximum Distance The Maximum Distance attribute determines how much of the scene is sampled. Think of this as the distance the secondary rays travel in the scene as they search out nearby surfaces. If a nearby object is beyond the Maximum Distance, then it will not affect how ambient occlusion is calculated because the secondary rays will never reach it. When Maximum Distance is set to 0, the entire scene is sampled; the Max Distance is essentially infinite.
One of the best ways to increase efficiency in the scene is to establish a value for Maxi- mum Distance. This decreases the render time and improves the look of the image. Deter- mining the proper value for Maximum Distance often takes a little experimentation and a few test renders. You want to find the value that offers the type of shadowing you need within a reasonable render time.
10. Set Maximum Distance to 4. Leave Spread at 0 (see Figure 12.25).
At this point, these settings should produce a nice-looking ambient occlusion pass for this scene. Now you need to associate this pass with the helmet render layer. To save some render time for this exercise, the other render passes created earlier in the chapter can be deassociated.
11. On the Passes tab of the Render Settings window for the Helmet layer, select AO in the Scene Passes section, and click the icon with the green check mark to move it down to the Associated Passes section.
12. Shift-select the depth, diffuse, reflection, shadow, and specular passes in the Associated Passes section so that they are highlighted in blue.
13. Click the icon with the red X to move them back to the Scene Passes section. This means that they will not be calculated when the Helmet render layer is rendered (see Figure 12.26).
Figure 12.25 The Use Local AO Settings feature allows you to adjust how the ambient occlusion will look when the AO render pass for the Helmet layer is created.
Even though you have set up the AO layer and associated it with the Helmet render layer, the ambient occlusion will not calculate correctly until you enable Ambient Occlusion in the Features section of the Render Settings window. This is an easy thing to forget!
14. Click the Features tab of the Render Settings window.
15. Under Secondary Effects, select the Ambient Occlusion option (see Figure 12.27).
16. Open the Render View window, and create a render using the renderCam camera. You won’t see any ambient occlusion in this render; however, it is being calculated and stored as a separate image.
The pass is stored in a temporary folder in the project’s Images directory. If the scene uses layers, each layer has its own subfolder where the passes are stored.
Figure 12.26 Calculation of the other render passes is disabled by mov- ing them from the Associated Render Pass section up to the Scene Passes section.
Figure 12.27 Turn on Ambient Occlusion on the Features tab of the render settings.
17. To see the Ambient Occlusion pass, use the File menu in the Render View window.
Choose File Load Render Pass AO. The image opens in a separate image view window (see Figure 12.28).
18. Save the scene as helmetComposite_v04.ma.
To see a finished version of the scene, open the helmetComposite_v04.ma scene from the chapter12\scenes directory on the DVD.