Motion blur not working with animation

[TeoRossi93]

Hello guys

I'm trying to render motion blur of some animated spheres that build a bigger one using metaballs. Since the animation is pretty heavy I decided to bake an alembic file.
This alembic unluckily isn't working with motion blur, as you can see in attached image the blue spheres are alembic object moving (all sphere going to the center) while the red sphere is just a normal sphere animated; motion blur works on the red one.
How could I fix this?

[mmarcotic]

Hello,

I just tried animating alembic-cloned sphere in a simple scene and for me, motion blur is applied as expected, so I would presume that the culprit for this issue is elsewhere. Would it be possible to send us your scene? You can do that by attaching it here or by using https://corona-renderer.com/upload for more secure projects.
Also, feel free to try Corona Proxy as its purpose is very similar to Alembic.

Thank you,
Jan

[TeoRossi93]

Hello Jan,

I uploaded the scene, file name is 01_Fusione_0009.c4d.
I still have to try with the corona proxy

[BigAl3D]

I would suspect it's the Metaball Object. Corona works with so much of C4D, but funny things with Mograph Instances, the Background Object and I suspect Metaballs too. You didn't mention if the red sphere was also a Metaball. Is saving to Alembic a form of baking all the animation into the scene? If so, you should be able to scrub the timeline without weird things happening. Is the animation playing out as expected, with the Metaball effects, just without blur?

[Cinemike]

Corona Motion Blur does not work (yet) with deformations (like a bend deformer or joints) or changing poly count (like metaballs), so your guess might be quite right.
Changing poly count seems to be a no-go for many MB algos, the native C4D renderer can use something called "sub-frame motion blur", which renders each frame several times with a slight time offset and calculates a blurred image from that (which is plainly insane due to the huge rendertimes for a single composite frame).

CU
Michael

[mmarcotic]

Yes to what Cinemike said - motion blur has its flaws in Corona and this will be one of them - I even tried a simple scene with Attractor and motion blur was nowhere to be found, it seems that it really works only with position changes at the moment. I will write this down as a feature request.

Thanks,
Jan

[TeoRossi93]

Oh gosh, that's a shame :( I think I will try to fake blur in after then
Thank you guys

[BigAl3D]

@TeoRossi93 I remember my old post about the Velocity Pass not working, at least on the Mac. That was going to be my workaround for motion blur, but neither of them work.

[Cinemike]

Now I don't know many render engines, but is it in any of them actually possible to render motion blur with frames/objects of changing polygon count? Without having to render them x times, of course.
Just curious.

[Nejc Kilar]

Now I don't know many render engines, but is it in any of them actually possible to render motion blur with frames/objects of changing polygon count? Without having to render them x times, of course.
Just curious.

Yep, I think its called vertex motion blur typically.

[Cinemike]

I think it's very difficult to make sense of a constanty changing topology and altering vertex counts. How would you determine the motion from point A to point B when vertices appear and disappear "randomly"?