Tser

Mirko Jankovic
"All you need is a Grid to catch the Shadows, an Environment image (eg. HDRI) to cast the rays and Objects you want to cast Shadows from."

Just to check, catcher can only be grid or it can be any other object in the scene as well?
I mean wording seems a bit exclusive to grid so figured to check.

Catcher was designed on a Grid and the algorithm automatically trims up the Grid like trimming off fat from a piece of steak, but, I created a sphere Radius 50x10x50 Center 0x-10x0 with Rows/Columns = 50 and used it instead of the Grid and it worked, as you can see, the underside of the squashed sphere also catches the Shadow, I don't think it would be a good idea to have a 3D object catching the Shadows, but a 2D object (without a bottom) would be fine:

Well I have released it a bit earlier than expected, I've just spent days of constant testing to make sure it does what it's supposed to, I had an issue with the catching Grid loosing the material, but only if I had the blackboxed version on it's own in the /otls folder, if the un-blackboxed version was in the folder also there was no issues, go figure, but it has been tested on multiple machines now with the blackboxed hda only in the /otls folder and all is well.
The Gumroad page is:
https://houdinishadowcatcher.gumroad.com/l/gggwv [houdinishadowcatcher.gumroad.com]
I hope you like it...

I have finally completed all the testing on my Houdini Karma XPU/CPU renderer ShadowCatcher, it is a Shadow Catcher unlike the version which comes with Houdini v21, it works on the Material level using a MaterialX material in the Beauty pass, so, no need to composite the Shadow after the scene has been rendered. It interacts with materials in the scene and in refraction's and reflections, it is very fast using the multi-threaded CPU prior to the render. Now we can all have a Shadow Catcher in Karma like all the other renderers out there, quick, easy to setup and very stable.
It is available on Gumroad:
https://houdinishadowcatcher.gumroad.com/l/gggwv [houdinishadowcatcher.gumroad.com]