This example shows how the Hit ID attribute can be used to determine which collision object a particle hit last. After a particle bounces off a grid, its color is changed according to the ID of the collision object.
Essentially, there are four collision objects. When a particle hits the collision object, it bounces and its “hitid” attribute is set to a value dependent on which object it hit. The value is specified by the “Hit Index” parameter in the Behvior tab of the Collision POP.
The Color POP is then applied to set the color based on which object the particle hit last. The lookup value is based on the $HITID variable.