Possible bug with Sweep Growth Render?

[dean]

I’m animating a Sweep Object length with End Growth 0-100%. Got files back from render farm and thought it was a problem with the farm render.

In the IPR, it renders fine, but a Picture Viewer render, it cuts off the last bit of the sweep before the Cap (with or without Fillet). In fact, the PV render isn’t actually rendering the complete frame content (Torus has started to fill in IPR below).

Dean

[dean]

And the next frame completely messes up...

v2.2.0

R18.057

[peter.horvath6V6K3]

That's odd. The export logic for PV and IPR is the same, so the result should match. Could you please send me this scene or a simple one, so I can take a look?

[dean]

Hi @Peter Horvath

Many thanks for looking, here’s a stripped down scene file. R18.

glitched-oil-arn-321c4d.zip

[peter.horvath6V6K3]

The difference is caused by motion blur. IPR renders without motion blur by default (you can enable it in the Render menu). It's a result of the changing topology of the Sweep object, I'm not sure if it's a bug or a limitation. I will take a closer look tomorrow and let you know.

[dean]

Ah, yes, I was endeavouring to use this technique to get an AOV vector motion for RSMB in AE.

I’ll default back to re-rendering the scene in C4D to get the Motion Vector Pass.

[peter.horvath6V6K3]

The problem with the motion blur is a technical issue. The Symmetry and Sweep objects are so called object generators, which generate new polygon objects to the scene transparently in each frame. There's no way (I know of) to identify these generated objects within frames, therefore I use the order of the objects. The problem is that the order in the Symmetry object changes frame by frame, so the transformation matrix in the motion steps (with mode set to 'center on frame') are messed up.

I'm not sure I can fix this with the limitation of the C4D SDK.

Deformation blur could be also a problem because identifying vertices and polygons between frames in a changing mesh is not possible either.

[dean]

Thanks for the info - I had thought it would be something to do with geometry generation. between frames. Useful to know.