Reflection Render Layer Retain Material of Reflection Catcher?

[bkirch]

Spinning my wheels on this one... but probably it's an easy solution I haven't thought of or come across.

Say I have a chrome sphere on a checkerboard floor. I want to make a Maya render layer that is the reflection of the chrome sphere into the floor, with alpha of the reflection. However, I want to retain the floor's checker material so that it's both casting reflections into the scene (onto the sphere) and acting as the reflection catcher.

Is there way to do this in one render layer? Using Maya 2018.5 + V-Ray 3.60.04


Thanks,

-Brian

[yolov]

I'm not entirely sure what the purpose is. In any case, you could try and see if it helps to use the MaterialSelect render element - just connect the plane's material to it and it will produce a pass that's the same as the beauty, but masked only for the plane in your case.

[dgruwier]

Not sure what you want exactly, but there are some options to get an alpha for the reflection itself. For example you can add an extra tex pass with a VRayDirt material, and set Occlusion Mode to one of the "Reflection occlusion" options. Increase the radius and use the Result Affect or Exclude options to ignore other objects, until you get a nice clean matte for the reflection of the sphere.
You can also just create a render layer where the sphere has self illumination, and remove all other lights and objects and disable primary visibility for the sphere, that will get you a matte that is more precise if your material is very complex.
This in combination with object mattes and a multi-pass render should let you do almost anything you want with the reflection.

[bkirch]

Thanks for the replies.

What I am doing is integrating CG elements onto a live action plate of a high-rise building window exterior. So, let's say I have a plane geo standing in for this glass exterior. I camera-project the backplate as a VRayLightMtl onto the plane to reflect into the CG object I have sitting on the glass. The glass exterior plate is not only glass, but window panes dividing sections of glass, like a grid pattern. This pattern is visible reflecting onto the CG object...

..then I want to create a reflection-only render layer of that "glass" plane which has the CG object reflecting onto it, with this backplate material still visible on the CG object. And I want to have one render layer for this result. Up to this point I've been making a material override on the plane with a VRayMtl that is black and reflective, and having the plane in a VOP node with Matte properties active to cut out the alpha. This works to some degree, except for the lack of backplate material reflecting onto the CG object. Also, I found that any render elements passes do not reflect properly onto an object with Matte properties active.

dgruwier, @yolov: I'll try out these methods to see if a combination of them will achieve all of the following:

1. retain the backplate material reflecting on the CG object
2. cut out alpha of the reflection
3. reflect render elements onto the plane
4. have one render layer for these results


Thanks,
-Brian

[GoodbyeKansas]

What you can do is add Vray overrides to the shading group of your material. Then connect your projection to the environment override slot. I think that would work. You mat also need to fiddle around with settings on the vray properties. Look for “without projection map”. I think that would work.

—Hannes

[bkirch]

I hit a wall pretty quickly because the inherent challenge in what I am trying to do is get the same "glass" geo to both cast a reflection into the scene (using the backplate projection VRayLightMtl) and also be the reflection catcher (using a black reflective VrayMtl). I could do this with two copies of the glass geo with these two different materials applied, then use Maya layer collections to control visibility, and also use reflection exclusion lists in vop nodes so these two meshes don't reflect each other. The catcher meshes can't be coplanar, so one geo has to be slightly offset in space. I still don't know how to get a matte surface to reflect render elements. I have to make a separate layer for that with matte turned off. But at least I can get the backplate casting into the scene.

[bkirch]

GoodbyeKansas I did not see your reply before posting. That's a very cool method I did not know about. I'll mess around with it and see what happens.

[bkirch]

"...settings on the vray properties. Look for “without projection map” "

GoodbyeKansas - What do you mean by vray properties? A vray object properties node? I cannot find anything named "without projection map." Thanks.

[GoodbyeKansas]

Yes on the vray properties set. Under matte properties, enable "matte surface" and under attribute "matte for all secondary rays" you have the option "without projection mapping"