Forums Solaris and Karma XPU Light Linking

XPU Light Linking

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d3zd3z
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The release notes for 19.0.423 suggest that light linking should be working on Karma XPU. The attached hip file has two boxes, the left with a glass pane. I have the light linker setup so the glass doesn't cast shadows with the lights. With the CPU, this renders as expected, but with XPU, it appears that none of the light gets past the glass.

Did I misunderstand the release note, or am I otherwise doing something wrong?

Thanks,
David

Attachments:
karma-glass-cpu.png (1.3 MB)
karma-glass-xpu.png (826.7 KB)
glass-lid.hiplc (1.5 MB)

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jsmack
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d3zd3z
The release notes for 19.0.423 suggest that light linking should be working on Karma XPU.

Perhaps the release notes meant that light linking, specifically, was working and did not include shadow linking.

Shadow linking does not appear to be implemented in XPU yet.

To let light through the glass, shadow linking isn't necessary. Using 'fake caustics' would achieve the effect of the glass allowing light through. Use the mtlx fake caustics node in line with the mtlx shader and the collect vop of the material x network.
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d3zd3z
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I did try the fake caustics as well. It does indeed light the inside, but it also distorts the view through the glass. I guess it is being faked in both directions?

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fake-caustics.png (1.0 MB)

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jsmack
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d3zd3z
It does indeed light the inside, but it also distorts the view through the glass.

I noticed that about XPU. There appears to be a bug with enabling fake caustics with XPU and refraction.
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d3zd3z
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Unfortunately, it looks like this means there isn't any way to properly render this "donut under glass" with XPU. For my current scene, I've kind of worked around it by just disabling the glass entirely, as the object isn't that large in the scene.
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jsmack
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d3zd3z
Unfortunately, it looks like this means there isn't any way to properly render this "donut under glass" with XPU. For my current scene, I've kind of worked around it by just disabling the glass entirely, as the object isn't that large in the scene.

It works without distortion using true caustics. It takes more samples to converge, but with XPU samples are cheap.
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d3zd3z
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Even with many times the number of samples, 1. it still seems pretty far from converging, and 2. the result is darker. I'm not sure where the darkness is coming from, this glass material should be letting all of the light through.

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true-caustics-xpu.png (1.9 MB)

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jsmack
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d3zd3z
Even with many times the number of samples, 1. it still seems pretty far from converging, and 2. the result is darker. I'm not sure where the darkness is coming from, this glass material should be letting all of the light through.

It probably won't converge easily with a small light source like that, but it does okay with a more diffuse env type light. The energy loss comes from the color limit, which defaults to 10. raising it to a million seemed to help, but there might be other energy losses still.

Ideally, refraction with with fake caustics will get fixed for XPU.
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brians
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There are still issues to sort out with fake-caustics on XPU.

But in the meantime, to remove the refraction effect from the glass you can set it to "thin-walled"
Alternatively, you could also set the IOR to 1.0, but that might affect the Fresnel reflection a little.

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brians
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Oh and to confirm

In XPU...
- LightLinking is working
- ShadowLinking is not working

https://www.sidefx.com/docs/houdini/solaris/karma_xpu.html#lighting [www.sidefx.com]
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AnimGraphLab
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Just for someone figuring out how to actually link specific light to a specific geometry.

And to create a shadow link: hold Alt + LMB and drag the light in the middle (have a look at the link after last GIF).





You can also drag lights (from the right to the middle) to create a rule specifically for that light.




https://www.sidefx.com/docs/houdini/nodes/lop/lightlinker.html [www.sidefx.com]
Edited by AnimGraphLab - 2023年4月7日 09:59:28

Attachments:
houdini-karma-render-light-linker.gif (8.2 MB)
houdini-karma-render-light-linker1.gif (11.9 MB)

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Alex Frenklakh
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Update.. XPU Shadow Linking does not seem to be working as of right now, still.. double checking with SESI..
Edited by Alex Frenklakh - 2024年3月20日 20:20:52
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vvzen
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I didn't check with Support, but it still seems to me that XPU Shadow Linking is not working.
I can see that with my current setup, same exact scene, just flipping between Karma CPU and XPU still allows one shadow to be casted where it shouldn't (see screegrabs below).

PS: This is on 20.5.654, but I just saw that it's still not supported [www.sidefx.com]
Edited by vvzen - 2025年8月3日 17:04:38

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light-lighting-bug-karma-cpu.png (989.5 KB)
light-lighting-bug-karma-xpu.png (988.9 KB)

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Heileif
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vvzen
I didn't check with Support, but it still seems to me that XPU Shadow Linking is not working.
I can see that with my current setup, same exact scene, just flipping between Karma CPU and XPU still allows one shadow to be casted where it shouldn't (see screegrabs below).

PS: This is on 20.5.654, but I just saw that it's still not supported [www.sidefx.com]



You will probably see this in the next major version. https://www.sidefx.com/forum/topic/98087/ [www.sidefx.com]
Edited by Heileif - 2025年8月4日 06:18:42
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brians
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This is visible in the new Houdini 21 sneak peek video credits
https://www.youtube.com/watch?v=aq7JQCV51CY [www.youtube.com]

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xpu_h21_sneak_peek.png (188.4 KB)

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