Setting the Global Ambient Occlusion Options

To enable ambient occlusion with caching

1. Enable ambient occlusion.

   By default, ambient occlusion is enabled for the scene and the ambient occlusion cache is turned off. In this mode, no actual computations will occur until you have connected the Ambient Occlusion shader, which is responsible for initiating ambient occlusion calculations on demand. If this shader does not exist in the scene, there is no overhead — it's the same as compared to scenes rendered with ambient occlusion turned off.

2. Set the quality of the ambient occlusion by specifying the number of ambient occlusion Rays to be used for the computation of each ambient occlusion value.

   NoteThe Rays value is used instead of the Number of samples value specified in the ambient occlusion shader, when the Number of samples is set to 0.0. As long as the ambient occlusion shader has its Number of samples set to a positive non-zero value, then the Rays value is ignored.

3. Enable ambient occlusion caching for a gain in overall rendering speed. This caching mechanism is similar to that of final gathering, where occlusion values are precomputed for distinct points only and stored in a 3D map data structure for fast lookup and interpolation during the final rendering.

   Caching performs several preprocessing passes of ambient occlusion computations in order to fill the cache before rendering starts. This preprocessing is done regardless of any actual requests from the ambient occlusion shader. In the first preprocessing pass, some ambient occlusion points are created on a coarse grid, and then subsequent passes refine the grid adaptively.

4. The Density of the grid is determined by setting an upper bound for the number of ambient occlusion points per pixel.

   When your scene varies a lot in terms of color, both the Rays and Density settings can be used to retain the detail by sampling more of the scene. In the case where there is a fair amount of geometric detail on the object being occluded, then increasing the density of the map can help to capture more of the details on that object, independent of the ray count.

5. During tile rendering, ambient occlusion values are interpolated from the specified number of ambient occlusion cache Points closest to the lookup location.

   Note The ambient occlusion shader is also used by both RenderMap and Ultimapper to generate ambient occlusion maps. Make sure that ambient occlusion is enabled for the scene and keep in mind that the caching results are not captured in the ambient occlusion maps generated by these tools. For more information about using RenderMap and Ultimapper, see Specifying the Surface Map Type and Transferring Surface Attributes (Ultimapper) [Texturing].