Adding correct derivative computation. Based on "RenderMan for Everyone" course 25 - Siggraph 2006.
Adding correct derivative computation. Based on "RenderMan for Everyone" course 25 - Siggraph 2006.


danieldresser/cortex,goddardl/cortex,hradec/cortex,hradec/cortex,goddardl/cortex,davidsminor/cortex,lento/cortex,hradec/cortex,davidsminor/cortex,davidsminor/cortex,goddardl/cortex,appleseedhq/cortex,danieldresser/cortex,danieldresser/cortex,lento/cortex,appleseedhq/cortex,appleseedhq/cortex,lento/cortex,danieldresser/cortex,davidsminor/cortex