Custom Displacement Shading – Tracks in the Snow

Jun 302008

Here is another video I developed for Pixar’s RenderMan University, this one demonstrates an interesting techniques that can be achieved with a fairly simple custom displacement shader that relies mostly on an understanding of the fundamentals of computer graphics. Specifically, the technique uses a sequence of depth maps (shadow maps) rendered from beneath the surface capturing the distance from the shadow camera to each point on the displacement-mapped spheres. Each point can then be transformed into world space and used as an exact displacement amount for an object pressing into a surface. The effect of using a single depth map for displacement is show below:

And of course, to achieve persistence, you need to accumulate the depth maps per-frame and use the running total to displacement the current frame. The Courseware goes into detail about this process showing how to do this by either writing an external Python script or using It and Iceman, RenderMan Studio’s internal compositor and scripting language.