Make objects change color during collision?

Question

Hello there,

I'm using blender to create an animation with 150 objects. These objects each have an individual material with a simple Emission node, in which it's base color (RGB) has been individually keyframed and animated to produce color patterns and effects between all 150 objects.

Check exemple here:

This was achieved by individually keyframing certain colors onto 1 object, then copying those keyframes and pasting them onto the other 150 objects in specific timings to create the final color pattern animation I desired.

As I'm still quite new to Blender, I was hoping to learn and understand if there is a more effective way of achieving these results. I've seen that perhaps I could set-up a Constraint or Modifier that would make the 150 objects change color based on colision with other objects.

As an example of what I'm trying to explain, I will attach these gifs below:

(Object colliding with spheres)

(Same prespective, but the object is hidden. Spheres change color during collision with said object)

(Final result: notice the colors changing)

Note: these gifs are just a representation of what I intend to achieve - the colors were changed manually.

Do you think this can be done with Blender (or any addons)? If so, I would appreciate any help!

Thanks for your time and support.

Answer 1

This question is tricky to answer briefly, because you have so many options open to you. All these examples are Geometry Node groups, working on animated mesh-objects comprising vertices without faces or edges. All the GN groups store colours on the mesh, in an Color Attribute layer, on vertices. Your exporter should be able to pick up the locations of the vertices, and the colours stored on them.

In order to be able to see the effects, a simple supplementary GN group is added at the bottom of the modifier stack, instancing an icosphere on each vertex, with an associated shader:

I imagine the exporter would work on the meshes with this GN group silenced.

Interactions with external meshes

Your example shows a test for inside/outside an external mesh, switching colours accordingly. This can be achieved by firing a ray from your vertices, and testing to see whether the hit face is backfacing to the ray:

This example allows you to set ray direction and length, inside & outside colors..

... or you could vary the color of your points according to their proximity to an external mesh:

effects analogous to this:

Or, for perspectival effects, you could treat your points as a projection-plane. Here an eye-point is set up behind the points, and rays are fired from there, through the points, at the target object. The color of the points reflects whether or not the target is hit:

.. for results like this:

Or, just work with textures

Sometimes, there may be no need for external objects, and you could just work with textures. They can be 3D, calculated from the positions of the points in the point-object's space, or 2D, projected through the point-object, or perhaps based on some UV-mapping of the points. The same techniques apply here as would in any shader-tree.

Here, an animated mix is made between 'Bands' and 'Spherical' Wave textures, through the points, while the points themselves are animated. The possibilities here are as wide as with any other procedural texturing.. (endless). Or, with suitable resolution in your points, you could compose your own image-textures or movies in any application to project through the points.

If you need any particular effect, it would probably be worth posting a question specific to it.