Karma motion blur

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Hey, I'm having trouble finding information on Karma since it's so new, I haven't been able to figure out how to have motion blur, has anyone done this in Karma?

It's probably really simple and in-front of my face!
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Well according to this, you can do motion blur with Karma:

https://www.sidefx.com/faq/karma/ [www.sidefx.com]

Looks like all you have to do is set you camera shutter open/close parameter, then make sure “Instantaneious Shutter” is not checked on Karma.
Edited by BabaJ - 2019年12月31日 18:21:37
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Yup, you'd think that would work, but no go just did another test scene to try it and it seems the Shutter open and close times do nothing.

Also Instantaneous shutter doesn't seem to be affecting the render
Edited by 3dspline - 2019年12月31日 18:50:34
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You're USD file needs to have multiple motion segments. In the viewport, having a cache LOP should enable this for preview rendering.

The alternative is to use velocity motion blur.

There are some known issues with motion blur on nested instances which we hope to address in the new year.
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You're USD file needs to have multiple motion segments. In the viewport, having a cache LOP should enable this for preview rendering.

The alternative is to use velocity motion blur.

There are some known issues with motion blur on nested instances which we hope to address in the new year.

On the USD interest group there is some ambiguity on the intended interpolation scheme for transform time samples. While hydra performs a naive interpolation, Seb stated at pixar, they leave it up to the host to perform optimal interpolation directly from the raw time samples. I've noticed discrepancies between mantra's motionblur of packed primtive transforms and xform timesamples interpolated by hydra with Karma. Will there be an option in the future for improved xform interpolation with offline renders?
Edited by jsmack - 2020年1月1日 02:33:25
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Was the discrepancy using packed fragmanets with RBD? Packed fragments support angular velocity which is currently not supported in Solaris/Karma.

I think the xform interpolation will likely be left to the client. USD/Hydra really just provide the raw data. Though, I could see USD/Hydra providing utility functions in the future that provide consistent interpolation across delegates, I don't think this is in yet.
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Was the discrepancy using packed fragmanets with RBD? Packed fragments support angular velocity which is currently not supported in Solaris/Karma.

I was comparing a ‘crag’ test geometry render between mantra and karma. Which I think is plain packed geometries. I rendered it in mantra using 2 geometry samples with and without a time blend, with and without “smooth interpolation of packed transforms” and all looked a little different from the karma result. The main issue was karma seemed to render ‘false’ blur, motion where none was present in the apparent data.
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There is a known issue with transforms on instances (compared with references) in USD/Solaris/Karma right now, not sure if crag is a different case though. I'll take a look into this tomorrow. This also might be related to an existing bug (99069).
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Hi

I have gone through docs, forums etc and cannot get any kind of motion blur working in Karma. I have added the cache node. I have increased the distance between shutter open and closed to maximise the effect of motion blur. Nothing works. I just wnat to see motion blur when I change my viewport from Houdini GL to Karma.


My other question is the docs say in order to save out you usd geo to motion blur in the future you need to change the data. What data where? I have Multiverse USD install in Maya and for an idiot like me it is super straight forward to see how to export sub-frames for motion blur. How do you do this in Houdini?

Screenshot of multiverse usd write from Maya
https://paper.dropbox.com/doc/Write-USD-Asset-87RXiZG8ex6z7EAh6unM0 [paper.dropbox.com]

All the best
Mark

Attachments:
introTo_usd.hipnc (802.0 KB)

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There is blur in the file now that I added the render geometry settings node which lets you assign motion blur and time samples - since you animated at the geometry level you need Geometry Time Samples - if you were animating at the xform level then Transform Time Samples would work.

The key is to make sure this node is assigned directly to the primitive. Then it works.

Attachments:
introTo_usd_blur.hipnc (837.0 KB)

Robert Magee
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Hi. Thanks for that. It was driving me bonkers. So I thinknow our work flow is going to be alembic cache out of maya. Sop create the alimbic in lops and export with the render Geo settings node directly underneath the Sop create and then add the usd render rop. Have I got this correct to create the usd file? Best mark
Edited by Mark Wallman - 2020年3月4日 15:12:32
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Mark Wallman
Hi. Thanks for that. It was driving me bonkers. So I thinknow our work flow is going to be alembic cache out of maya. Sop create the alimbic in lops and export with the render Geo settings node directly underneath the Sop create and then add the usd render rop. Have I got this correct to create the usd file? Best mark

Don't import the alembic with a sop create, the whole cache will be output to the usd again. Either reference or sublayer the alembic. If you reference the root of the alembic, you can add the render geometry settings to the reference prim. Although if you are using multiverse to output usd, why not sublayer or reference the usd? It should get better performance than alembic.
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Hi.thanks. I am planning for both having usd export in maya and not. It depends on our it administration. Once in houdini although it is an extra step I want my students to only think of rendered Geo as usd not abc to keep it one format. Lots of digging around for me! Thanks for your help. As a side comment you have tons of other usd files se have given. It could be good to do one with really simple motion blur. Crag, propellers etc
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One advantage of using USD files for your sequences is that you don't need the cache node to get motion blur to work.
Robert Magee
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Another tip - Currently, Shutter Open/Close on the camera node will affect motion blur when you render to disk but doesn't affect motion blur in the viewport. These kinds of details are why Karma is still in beta.
Edited by rmagee - 2020年3月5日 15:30:54

Attachments:
image (5).png (1.7 MB)

Robert Magee
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rmagee
Another tip - Currently, Shutter Open/Close on the camera node will affect motion blur when you render to disk but doesn't affect motion blur in the viewport. These kinds of details are why Karma is still in beta.
And here I thought that the advantage of USD and Hydra backend would be parity between Viewport and Disk Render without having to do extra work on renderer side, I guess nothing is as easy as it seems at first
Edited by tamte - 2020年3月5日 15:49:29
Tomas Slancik
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Hi

Thanks for the heads up. Out of interest has anyone tried this with Renderman?

Best

Mark
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Mark Wallman
Hi

Thanks for the heads up. Out of interest has anyone tried this with Renderman?

Best

Mark

I tried with RenderMan 23.2 and Houdini 18.0.391, I can get geometry motion blur with only 1 sample, I can't find any way to add more geometry samples. Also I didn't find any way to add velocity motion blur in RenderMan inside Solaris.
Both geometry motion blur and velocity motion blur working fine with Karma.
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That's definitely a bummer, thanks for the update on the Renderman front.

@SideFX is it an issue on your end or a problem w/ Renderman? If it's on your end, any ETA on a fix?
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I've been trying to get Renderman 23.2 to blur geometry in Solaris via the ‘v’ attribute and having no luck. With some twiddling I can get Karma to blur it. But not Renderman.

I can get transform motion blur to work in Renderman, however. I have to use the Cache LOP.
I also tried renaming ‘v’ to ‘velocity’ but had no luck
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