Arnold lights not being motion blurred

[kenn...@gmail.com]

Hello,

We noticed that Arnold lights are not being motion blurred in a batch render.

Linked here is a simple example scene to reproduce this issue.  Included in the scene are:

• 1 aiPointLight (blue)
• 1 aiQuadLight (red)
• 1 aiMeshLight (yellow)
• 1 geo sphere (green)

In the interactive render, as expected, there is no motion blur.

In batch render however, we are seeing the geo sphere being blurred as well as the mesh light.  But the lights are not.  

Is this a limitation/known bug or are we missing some a setup in Gaffer to make Arnold lights render with motion blur?  Running a similar test in MtoA lights are motion blurred properly.

Best,

Kenny

This was tested on Gaffer 0.59.6.0 with Arnold 6.1.0.0

[John Haddon]

Hi Kenny,

I checked, and as far as I can tell we are correctly exporting motion blur for lights when going to Arnold. The problem looks to be that Arnold doesn't handle motion blurred lights correctly if the shutter interval isn't `shutter_start = 0, shutter_end = 1`. Could you check if your MtoA example puts that shutter interval in the ass file? I've attached a very simple ass file which has a point light and a sphere moving at exactly the same speed, but where the point light ends up with a completely different motion trail. If you change all the `shutter_start/shutter_end` and `motion_start/motion_end` values to `0/1` then it renders as you would expect. I'll report this to the Arnold devs now...

Cheers...

John

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[John Haddon]

Got word back from the Arnold devs - they have a fix for animated quad/point/sphere lights, so hopefully that will be available soon. Disk/cylinder lights don't yet have support for animation at all (for the camera-visible part, they work fine for illumination), so it sounds like that will take longer.

Cheers...

John

[Kenny Chang]

Hey John,

I took a look at what you mentioned regarding the shutter start/end values in MtoA and you are right, when it's set to 0-1 the motion trails match between geo and lights (quad, point) but does not match when shutter start/end values are not that (i.e., -0.25 to 0.25).  Doubled checked your example .ass file as well to make sure.  We can work around this until Arnold patches this issue.

Thanks for investigating!

Kenny