Emit only from where a mesh touches another surface

[stelees]

Hey there,
Is it possible to have mesh emit from a sphere (as a basic example) only when the sphere touches another object. So if it was an active body and was dropped onto a surface, only the parts of the sphere that touched the surface would emit, then if it rolled the parts that are touching the ground emit.

I was looking to see if there was a way to use the phoenix texture map or something, looking at wet maps and other random elements, but nothing that I could see fit the bill.

I looked in the particle tuner but there was nothing that I could trigger emission based on the distance of an object to another object, plus I wasn't sure if it would measure the whole sphere or just the polys that are within the distance check.

Any suggestions?

[georgi.zhekov]

Sounds like a job for the V-Ray Distance texture. You can find more about it here - https://docs.chaosgroup.com/display/...RayDistanceTex

Check this video on how it works - https://youtu.be/lTxD0xNVIyo?t=711
It's for fire/smoke but it should work exactly the same with liquids.

Using this method with Active Bodies will be a bit tricky though as Active Bodies are deleted and created again each time you run the sim. So if you add your active body in a source and then run the sim again it would disappear from the source.
What you can do instead is just run the sim with the Active Bodies until you get a result that you like. Then duplicate the clone and remove it from the Active Bodies render layer - this way you have the geometry with the animation baked in.
After that you will need to remove the original geometry from the Active Body solver so that you don't have two copies of the same geometry.

Then you can proceed and add the duplicated clone in a source and use the V-Ray Distance texture as a mask for the emission.

The downside of this method is that if you decide that you want to change something in the Active Body sim, you will have to go through the process again.

Hope this helps!

[stelees]

Perfect, I had tried that but of course came unstuck with the active bodies being deleted hence why I was thinking it must be something to do with the Phoenix texture instead. That is a whole lot of work around for something that about 5 people on reddit or instagram may accidentally see

I have a go at all that anyway just to see if I can achieve the result I am looking for.

thanks for the reply.