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We've been having some issues with V-Ray's renderable curves and its motion blur. I'll try to describe the issues here so it's reproducable.
Motion Blur failing when one curve is present without motion.
First off, an Alembic with one or two moving curves works with motion blur. However, once you duplicate one of the curves so you have a static one as well then none of the curves have motion blur when rendered.
Then grouping this curve and putting a single key on the group seems to fix the motion blur... until you move to a new frame (and/or back). Setting a key on the new frame somehow does not fix the motion blur anymore, it stills breaks it? The only way to get it to work again is to slightly nudge the group, and it renders with motion blur. It seems pretty inconsistent.
So we were thinking of doing a hacky workaround, like Grouping all curves, go to frame -100 key the group to move a bit. Then on frame -99 key it and reset it, so that all curves have at least some motion blur there. Which seemed to work, but then we got some cases where it stopped working too - however those seem to be hard to reproduce too. Similarly we tried doing a Bake Animation on the Group so it has keys (albeit static ones) on all frames, which also did not solve the motion blur issues.
Attached is a very simple reproducible example, open the scene -> render a frame between 1-18 (that's when moving curve moves) through RENDER_CAM. No motion blur, set one key on STATIC_CURVE, render and suddenly there is motion blur. Go to another frame, render... no motion blur. Go back to the frame where you set the single key, render, no motion blur. The same issue is present when both curves are in their own vrayRenderableCurve set.
Other notes:
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Aside of the above, what also stood out to me is that "intermediate object" curves are also being rendered. To reproduce, make a curve, make it renderable, add a cluster to the curve and reposition it. Render. Both the original intermediate curve shows and the deformed one. It should only render curves that are not set to intermediate objects! Now the only workaround for this is to go to all Intermediate Curve objects and set their visibility to False too.
Motion Blur failing when one curve is present without motion.
First off, an Alembic with one or two moving curves works with motion blur. However, once you duplicate one of the curves so you have a static one as well then none of the curves have motion blur when rendered.
Then grouping this curve and putting a single key on the group seems to fix the motion blur... until you move to a new frame (and/or back). Setting a key on the new frame somehow does not fix the motion blur anymore, it stills breaks it? The only way to get it to work again is to slightly nudge the group, and it renders with motion blur. It seems pretty inconsistent.
So we were thinking of doing a hacky workaround, like Grouping all curves, go to frame -100 key the group to move a bit. Then on frame -99 key it and reset it, so that all curves have at least some motion blur there. Which seemed to work, but then we got some cases where it stopped working too - however those seem to be hard to reproduce too. Similarly we tried doing a Bake Animation on the Group so it has keys (albeit static ones) on all frames, which also did not solve the motion blur issues.
Attached is a very simple reproducible example, open the scene -> render a frame between 1-18 (that's when moving curve moves) through RENDER_CAM. No motion blur, set one key on STATIC_CURVE, render and suddenly there is motion blur. Go to another frame, render... no motion blur. Go back to the frame where you set the single key, render, no motion blur. The same issue is present when both curves are in their own vrayRenderableCurve set.
Other notes:
- The order of the curves in the Maya DAG or in the vrayRenderableCurve set does not seem to change things. Similarly Renderable Curve attributes also does not fix it.
- Tested in Maya 2018.5 with V-Ray Next for Maya, hotfix 1 version 4.04.02.00010 from Nov 19 2018, 21:38:32
--
Aside of the above, what also stood out to me is that "intermediate object" curves are also being rendered. To reproduce, make a curve, make it renderable, add a cluster to the curve and reposition it. Render. Both the original intermediate curve shows and the deformed one. It should only render curves that are not set to intermediate objects! Now the only workaround for this is to go to all Intermediate Curve objects and set their visibility to False too.
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