Here’s an ICE tree that uses a simple two-state setup to gradually move particle colors through two gradients (in State 0, the gradient is from black to white, and in State 1, from white to black). Randomizing the End Time gives me some variation between particles, and I customized the Modify Particle Colors to use “time in state” so I could use that as the trigger test.
In the Modify Particle Color compound, I simply swapped Get Particle Age for Get Time in State.
Softimage 2013 SP1 included a fix for a problem (aka a crash) with the Simulate Bullet Rigid Bodies nodes and states.
So, when a customer asked us how to do a two-part simulation, I gave Bullet + States a try. In the first part, the objects drop onto an obstacle, and in the second part, another obstacle comes along and pushes some of the objects away. Like this:
Here’s the ICE tree. I used Test Current Frame to trigger the state change. I did try some other triggers, like Test Particle Velocity and Test Particle Size, but I got some weird results with those triggers. By weird, I mean things like some, but not all, of the small cylinders being pushed away, even though they were still in the first state.
The idea here is to push just the big cubes. I make all the little cubes passive, so they get left behind.