Particle Evaluation Question

[Anonymous]

I’m having a problem figuring out how particles evaluate in the graph, and I’ve distilled the issue down to a simple scene. I have a locator moving across a field of black particles. Using an if node, when the locator is within a certain distance of a particle, it turns from black to red. My problem is that I don’t see how to keep them red once they’ve turned so the locator leaves a trail as opposed to a moving red circle; the evaluation runs fresh with every frame, and I see no way to maintain a variable state. I know there's something simple I'm missing here.

How do you save a variable in a particle so it can be used in the subsequent frame?

[mjcg91]

You probably want to use the feedback port to save the new state of your particles.

[ken.ootani · Accepted solution]

example1 : use the feedback port .

example2 : use influence

example3 : edit simulate_particles

[ken.ootani · Accepted solution]

example1 : use the feedback port .

example2 : use influence

example3 : edit simulate_particles

[Anonymous]

That's awesome! Thanks so much.

One followup question: as I was working on this, I was looking into using feedback connections as a way to send data back upstream, but I don't see how to create them. I've seen feedback connections in compounds for things like velocity calculation, but see no documentation for how to create them.

[Grahame_Fuller]

You need a matching pair of input and output ports on a compound. Then on the inside of the compound, you can right-click on one of them, set it as a feedback port and specify its match.

There is some documentation in Create custom simulations.

I hope that helps,gray