Having a compositor built into a 3d program offers a new way to drive any parameter in the 3d app. Softimage (as well as Blender & Houdini) has an intergrated compositor. This tool opens many possiblilties. Here I used a Vector Paint node in Softimage's compositor to drive the value of a CutMap parameter on hair (grass). The effect works perfectly and can be tuned interactively in a 3d viewport.
If you are a Softimage user, download the supplied scene file below to view the setup:
| VecPaint_CutMap.scn |