Tser

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...

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.

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...