Odd behavior with Karma CPU

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Steven Quinones-Colon2: Member; 22 posts; Joined: June 2014; Offline

June 21, 2023 12:53 p.m.

I have an odd situation. I have a large USD file that I'm splitting into assets and doing lookdev as I go. When I render in XPU everything looks as I would expect it, but with CPU I get odd behavior, images below ,the first image is the CPU render. I'm on Houdini 19.5.368 on an M1 mac. The setup is really simple, any ideas?

Edited by Steven Quinones-Colon2 - June 21, 2023 13:05:49

Attachments:
network.png (300.9 KB)
Karma_CPU.jpg (173.4 KB)
Karma_XPU.jpg (155.1 KB)


mandrake0: Member; 636 posts; Joined: June 2006; Offline

June 21, 2023 2:21 p.m.

First Task: please update your Houdini Build to the Production Build (19.5.640) or Daily Build (19.5.653).

Since the Release of Houdini 19.5.368 there are +100 Bug Fixes for Karma, +150 Bug Fixes for Solaris, +70 VEX Bug Fixes and many +1000 other Fixes


Steven Quinones-Colon2: Member; 22 posts; Joined: June 2014; Offline

June 21, 2023 2:48 p.m.

Sure thing, will do. Thanks.


Steven Quinones-Colon2: Member; 22 posts; Joined: June 2014; Offline

June 21, 2023 3:08 p.m.

This renders are from 19.5.640, CPU first, I gamma them up so we could see better:

Edited by Steven Quinones-Colon2 - June 21, 2023 15:09:42

Attachments:
Karma_CPU.jpg (193.3 KB)
Karma_XPU.jpg (170.5 KB)


jsmack: Member; 7770 posts; Joined: Sept. 2011; Offline

June 21, 2023 5:09 p.m.

possibly a problem with the normal map. XPU and CPU behave differently with bogus normals. Many USD scenes I've encountered have all kinds of non-compliant and out of date problems with how they author materials, especially normal maps. Do they look the same if you disconnect the normal map from the material?


Steven Quinones-Colon2: Member; 22 posts; Joined: June 2014; Offline

June 21, 2023 7:37 p.m.

Actually I didn't add the normals yet because I was having this problem. I think is the geometry. The file was exported from Cinema4d. I'm surprised XPU can handle it, but CPU can't. Or maybe is that XPU is ignoring bad geometry and CPU is rendering it properly.

Attachments:
Screen Shot 2023-06-21 at 7.35.34 PM.png (2.0 MB)


mandrake0: Member; 636 posts; Joined: June 2006; Offline

June 22, 2023 8:03 a.m.

Steven Quinones-Colon2
Or maybe is that XPU is ignoring bad geometry and CPU is rendering it properly.

I would say maybe the Shader has functions / textures inside that XPU ignores and Karma CPU is using it. Or the Mesh has Attributes inside that gets wrong used.

What you can do:
Check the Mesh in Spreadsheet if there is something a Special Attribute or Normals(N) in Point or in Vertices you also can import in /obj and check there.
You can add for Testing a SOP Normal (Vertex or Point) and check if it is Better.
change the shader to a MTLX Standard Surface does it look same.
use a Default Mesh (Box, Sphere) and check if the shader works on both Karma(CPU, XPU)

I don't have a Apple M1 and i also don't know how XPU is Working on a M1 CPU/GPU.
When you find it could be a bug then it's required to report to Sidefx:
https://www.sidefx.com/bugs/submit/ [www.sidefx.com]


Andy_23: Member; 918 posts; Joined: March 2014; Offline

June 23, 2023 3:50 a.m.

I may add to this and am too having unexpected behavior with Normals using MaterialX standard surface.

I, too, find, that XPU gives me the expected results, while CPU there are obvious artifacts.
This happens with even the most simple geometry like grids.

Any help is much appreciated.

Running 19.5.640 — Apple Silicon M2 or Win 10

Edited by Andy_23 - June 23, 2023 03:58:17

Attachments:
karma_cpu_noise_bug.jpg (641.2 KB)


Andy_23: Member; 918 posts; Joined: March 2014; Offline

June 23, 2023 3:59 a.m.

Some artifacts with Principled shader, too.

Edited by Andy_23 - June 23, 2023 16:25:53


dlee: Staff; 425 posts; Joined: Sept. 2016; Offline

June 24, 2023 11:15 a.m.

Andy_23
I may add to this and am too having unexpected behavior with Normals using MaterialX standard surface.

I, too, find, that XPU gives me the expected results, while CPU there are obvious artifacts.
This happens with even the most simple geometry like grids.

Any help is much appreciated.

Running 19.5.640 — Apple Silicon M2 or Win 10

Can you please file a bug with the scene? Thank you!


Siavash Tehrani: Member; 710 posts; Joined: July 2005; Offline

Dec. 13, 2023 11:48 a.m.

We are seeing similar issues where Karma CPU has difficulties with normal "maps" generated from procedural patterns. Please see the example below: CAD file, normals driven by MaterialX procedural noises. Karma CPU has artifacts that line up with the model's topology, whereas XPU handles it fine. I will submit an official bug report as well.

The color difference is a separate problem that cropped up with H20, but I'll have to dig a little deeper on that.

Attachments:
KarmaCPU_Normals.gif (640.4 KB)
KarmaCPU_Normals.zip (315.8 KB)


jsmack: Member; 7770 posts; Joined: Sept. 2011; Offline

Dec. 13, 2023 1:44 p.m.

Siavash Tehrani
We are seeing similar issues where Karma CPU has difficulties with normal "maps" generated from procedural patterns. Please see the example below: CAD file, normals driven by MaterialX procedural noises. Karma CPU has artifacts that line up with the model's topology, whereas XPU handles it fine. I will submit an official bug report as well.

The color difference is a separate problem that cropped up with H20, but I'll have to dig a little deeper on that.

I wonder if XPU is using MikkT tangents and CPU is using ray derivatives as tangents--which will always be ugly for a triangle mesh


Siavash Tehrani: Member; 710 posts; Joined: July 2005; Offline

Dec. 16, 2023 11:56 a.m.

Interesting. Other issues I've come across with procedural pattern normals and Karma CPU are faceting, harsh shadow terminators with high-frequency noises, and artifacts where Rounded Edges does its thing.

We have a ticket in with support, hopefully they can sort it out.

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