user1111

Just detailing some of my experiences seeing if houdini would work on the Surface Pro 11 (Snapdragon X Elite) under emulation in Windows 11.

Out of the box it doesn't work, not for the ARM or emulation under PRISM reason as I thought would be the case but actually due to graphics. This is due to:

- Qualcomms GPU drives for Adreno are terrible, they support Direct X 12 and supposedly Vulkan but thats new.
- So no Open GL support, or Open CL support, which is not helpful!
- Microsoft have a compatability shim in the store that translates Open GL, Open CL and Vulkan (yes even though the driver does Vulkan supposedly) to DirectX12. This is available in the windows store.
- You can get native vulkan support by either removing the whole compatability pack or by deleting the dzn files in the folder (I can give details if anyone wants).

So out of the box Houdini crashes as the OpenGL shim does something it doesn't like. If you delete the files to get vulkan on the driver working it still doesnt work, I'm not sure if its because of the driver or if it's because it still uses some OpenGL things.

You can get it working however by using Mesa llvmpipe to do software open GL rendering, but the viewport is pretty slow. There is probably a configuration to get it doing open GL via DirectX12 or Vulkan (zink), but I couldn't figure it out.
To do this get the x64 (not ARM) mesa opengl.dll file and drop it in the houdini bin folder, set the environmental variables for the mesa driver and it should work. I haven't tried too much due to the viewport speed but will do so and update at some point.
There is also the Angle on Vulkan that does OpenGL ES which may be helpful, but I haven't tried yet.

So today I wouldn't reccomend it under windows, there is probably better luck under linux as the freedreno driver does do OpenGL but I think x64 emulation isn't as good.
Suprisingly though it's not because of ARM but OpenGL, which I wasn't expecting. Improvements to the Microsoft shim or the Qualcomm drivers may solve this though, or there might be some houdini env variables that may help.

I think you might want what is in the render geometry settings lop perhaps? For Karma you can set the holdout mode there for the geometry as None, Matte or Background.

Don't think it's correct but the best I could find was to put it in a add variant block in a for each loop with everything but the thing you want to be a new variant deleted (pack, delete everything else with a removepoint in a wrangle, unpack) using the contextoption("ITERATIONVALUE") to select the correct one.
Load as reference seemed to be required for me to get it to work, don't know USD enough to know why unfortunately. It's nearly procedural with the main value that has to be hand done is the total iteration number.
It's really a mess though, hopefully we get a node that takes packed prims and turns them to variants or from a sop attribute. Would be glad to see a better way than what I've kludged too.