Hi everyone,

I’m trying to create an interactive lighting setup in Houdini using Karma and would appreciate some guidance.

I have a floor made up of multiple individual boxes, all illuminated with the same white-colored light. A ball is bouncing across the floor, and I want the lighting or color of each box to change to blue whenever the ball makes contact with it.

Ideally, the effect would work dynamically: (https://www.youtube.com/watch?v=NuGATtVlXAU)

* All boxes start with white lighting.
* When the ball touches a specific box, that box changes to blue.
* When the ball moves away, the box returns to white (optionally with a smooth transition).
* The setup should work with Karma rendering, preferably in Solaris/USD.

What would be the recommended approach for detecting the contact and driving the color of the corresponding light or emissive material?

Also, would there be a simpler or more efficient way to achieve this using **Copernicus** in Houdini, particularly for handling the interactive lighting or color changes?

Any example node setups or guidance would be greatly appreciated. Thanks!

I don't think Karma or COPs have anything to do with it. Essentially, you have a color attribute on the boxes, and you're modifying it based on the distance to the ball—plus some algorithm. So, it's a geometry problem solved at the SOP level. The renderer simply visualizes that attribute; it doesn't care how or via what algorithm you're changing that color value.