Urgent - Vray GPU renders one of the materials in an animated sequence multiple times

[Alex_M]

I'm facing a serious issue when rendering an animated sequence of changing materials with Vray GPU. I have a pretty big project with hundreds of products, each of them in several different finishes. Each of the finishes is animated to change on every frame. The material change is done through a "Multi/Sub-Object" material and an animated "Material" modifier applied to the object. The problem is that Vray GPU always renders one of the materials twice (and sometimes even 3 times) if I render the animated sequence to the disk. For example, the material on frame 0 is rendered again on frame 1 and 5. If I do quick single renders of the frames manually (F9), they never repeat. This problem doesn't occur with the CPU renderer. Please check the screenshot below. Any way to avoid this?

[Joelaff]

Just guessing here. I would first look at where in the stack the Material modifier is. Try moving it up or down. Try adding an Edit poly on top of it.

Try adding some other animated modifier like a bend where you animate the bend direction while leaving the angle at zero (so it does nothing). The thinking being perhaps a modifier that changed the geometry will get updated properly rather than one that only changes material Id.

Good luck, and please let us know what, if anything, got it to work right.

…and of course send the scene to support so they can fix it.

[Joelaff]

Another thought would be to make sure the material is is being animated with step key frames. It could be a motion blur thing, or a rounding error based on the global time the material is sampled. If you don’t need motion blur turn it off.

[Alex_M]

Thanks for the suggestions, Joelaff . Unfortunately, none of them worked. I think I found a temporary workaround though. If I set the render output start frame in Render Setup to -1 instead of 0, Vray doesn't render duplicate images anymore. The drawback is longer render time since I'm rendering an extra frame.

[Joelaff]

Weird. I wonder if step key frames that you shift a half frame back in time (so the keys are not on the frames) would help. I swear I went through something similar that had to do with animating the material Id. I think I switched to animated textures instead.

Odd about the -1 start bit. You could put a big black plane in front of the camera at that frame so it renders instantly.

[hermit.crab]

Alex_M I'm glad you've found a workaround. Just for your information, the issue seems to be fixed in the latest internal nightly builds. Do try it out.

[Alex_M]

Great! I'd love to try it out. I don't see the nightlies when I log in though:

[hermit.crab]

Pardon, I thought you already have access to them. The fix is scheduled to be implemented in the next stable nightly build, which will be released soon enough.

[Alex_M]

Thanks, I got the download link now. I've just downloaded it and rendered a few scenes and everything works fine! No more repeated frames. Thanks so much for the quick response!