tomtm

Tser
When I set the render engine to XPU the render takes quite a bit longer than CPU, and I don't think you can get the same effect as a shadow matte (Shadow Catcher) with an environment light hdri, unless this ability is hidden somewhere.

I think it would be essential for later compositing where you load the background footage.
It would be cool to have a ShadowCatcher Material.

I agree that it is essential that Karma needs a Shadow Catcher, Pixar has one with their USD render engine, so it is possible with Karma, I think all current render engines have a Shadow Catcher, you just need it integrated with the Beauty pass, not just in a Shadow pass.

In XPU it gets a lot slower using the bg plate node, and also the glossy reflections feature is not supported from what I've tested. A shadow catcher would be great indeed.

johancc
In XPU it gets a lot slower using the bg plate node, and also the glossy reflections feature is not supported from what I've tested. A shadow catcher would be great indeed.

Ok, happy to see you guys see it also as an essential.
So I will send a feature request :-)

Is it now possible to implement a shadow catcher in 20.5?

I wonder if Copernicus can be used to generate a shadow matte?

Still looking for this solution all over the place.. no luck

Is there a chance that V21 has some form of Shadow Matte Material for catching shadows without involving the Background Plate and the compositor

Any updates on a Shadow Matte Material for H21?

It works just fine!

Thanks Mirko for the heads up, works really well and super easy to setup and thank to the great team at SideFX, well done.

Been testing the Shadow Catcher and it is VERY slow, I have two RTX 5090's and with the Shadow Catcher turned on the render update is agonizingly slow when panning the scene, or have I missed something?

Tser
Thanks Mirko for the heads up, works really well and super easy to setup and thank to the great team at SideFX, well done.

This is good news. I need to experiment with this.

Tser
Been testing the Shadow Catcher and it is VERY slow, I have two RTX 5090's and with the Shadow Catcher turned on the render update is agonizingly slow when panning the scene, or have I missed something?

I have noticed the scene navigation in solaris is much less responsive now with 21 and XPU viewport active. Not only with the shadow catcher.

Funny thing is, if I switch to Karma CPU rendering, not Karma XPU, then the scene panning etc is much more responsive, this doesn't make sense...

There are a few issues with this form of shadow catching in xpu, if you try to pan around the scene, the update takes a long time, even running two 5090 gpu's, also the shadow is not interacting with the object casting the shadow, if you select the option "Blocks Lighting" the render seems to pick up a black area from the background which is in the reflection of the object, maybe this is something to do with the shadow catching plane, also when you try to render to MPlay the shadow matte is not composited in the beauty, I would have thought that you would get the same beauty image which was displayed in the render view and the beauty pass is missing the area where the shadow was, there is a separate beauty and shadow, but you cannot composite them together, I just wish you guys followed the same method that Arnold uses by adding the shadow matte material to the plane, then everything in the scene will know that the shadow exists and react to it by adding it to their reflection/refraction's. I hope you can improve upon what you've started.

Looks like I'm back with the Arnold Renderer, the Karma Shadow Catcher just doesn't do it right, I was excited and full of hope, but it looks like the way Karma is set up that there is no way, using the current Karma methodology, to have a true Shadow Catcher material in Karma CPU or XPU. The current approach is composited after the scene is rendered, so the scene cannot react to the shadows in reflections, refraction's etc. I tried to create a shadow catcher node using the Mask by Attribute node which works to a certain extent, but it's not accurate enough to be truly convincing, although the scene does react to it's shadows. I cannot see why the Arnold Renderer amongst other renderers are capable of a simple Shadow Matte material, yet Karma, being a new guy on the block, doesn't have any interest in making such a required, fundamental function possible...

Tser
when you try to render to MPlay the shadow matte is not composited in the beauty, I would have thought that you would get the same beauty image which was displayed in the render view and the beauty pass is missing the area where the shadow was

When you have "Add holdout shadows to beauty" enabled offline render is indeed producing the same image you see in the viewport. The reason you see shadows in viewport but not in MPlay is because the viewport has lighter background by default, and MPlay has black background. If you composite the rendered beauty pass in comp (or change the background in MPlay via Load Background... menu and set it to something non-black) you will see the same image.

so the scene cannot react to the shadows in reflections, refraction's etc. I tried to create a shadow catcher node using the Mask by Attribute node which works to a certain extent, but it's not accurate enough to be truly convincing

If you seek accuracy or want to have shadows show up in secondary bounces, I would recommend using background plate workflow instead. The shadow catcher feature was added mostly in response to clients who seek simpler and easier solution where accuracy is secondary concern (e.g. drop shadows for graphic design work). Shadows are an absence of light - it's meaningless to reflect shadow when there's nothing being reflected to take light away from. Basically it's nothing on nothing (or black on black if you'd prefer). Background plate material allows you to project plate to the shadow catching geometry and serve as reflection source whose light can be taken away from (it infers how much shadowing should be present based on the plate colour and radiance, so it produces a lot more accurate shadow colour both in primary and secondary bounces, provided that the lighting set up closely matches the lighting condition in which the plate photo was taken).

I've submit bug and it is reported so should get it working properly soon. Problem is that at the moment shadow catcher deos not follow up matte render geometry settings as well, and it shows shadow even on object that should be matte. so hopefully it will be fixed at some point.

I decided to create my own XPU Shadow Catcher, this is a comparison of Arnold on the Left and my XPU Shadow Catcher on the Right,
no post processing...

A quick video