Hi,
I have two objects.
I would like one object to be invisible to the camera, casting a shadow and reflections but at the same time obscuring everything hidden behind it so that the alpha is transparent ( there should be a background in place of the object).
All in all, something like a Boolean operation, I cut one object with another but it needs all the shadows and reflections.
Any ideas how to do this?
Have you tried Corona ShadowCatcherMtl and setting the Alpha mode to “For Compositing”?
Technically, it works. Practically in a scene I have several shadowcatcher illuminators that illuminate my object with a schadowcatcher. Maybe I will change the scene.
I found an intermediate solution that works in my case. Double Sided material, where one is transparent.
Maybe you could also achieve this by using a Camera Map modifier in conjunction with a CoronaRaySwitchMtl.
The first one to put the background instead of the object itself, and the latter to replace its reflection.
I think I have managed to get what you need. 
Create a Corona Legacy Material (because it’s easier to get non-physical properties with it, such as lack of reflections).
Set its refraction to 1 and IOR to 1. That should make it “invisible”.
Under advanced options set alpha to “always black”.
Then plug a Corona Rayswtich Map into this material’s refraction color and make it GI - black, reflect - black, refract - white, direct - white.
It should also work with the Corona Physical Mtl somehow, but I haven’t tried it.
