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Physical Renderer motion blur + Xpresso is borking my scene

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I decided to make a separate thread, as the Expresso issue I thought I had was basically resolved over here:

However, my actual problem turned out to be something else...

I've attached a scene file for anybody who might be able to help. You'll need to cache the MoGraph manually using the tag, pre-cached was too big to upload.

If you go to frame 50 and render without Motion Blur active, OK, all is well and good.

Now re-render frame 50 with Motion Blur active.

The frame range from 40-50 is giving me no end of troubles...All I want is for the sphere to sit neatly on the clone while it wriggles and jiggles, and no intersections between the clone and the sphere...with Motion Blur!

This seems impossible to sort out, unless I'm doing something stupid, which is quite likely.

Any takers? I will be so grateful to fix this!


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As a last resort you can try caching both the sphere and the cloner with alembic.

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  • Don't you just love 'little investigations' with C4D?

    The screenshots from a new camera angle show what's happening: I've attached frames 49 and 50 to compare with / without Motion Blur.

    The renderer evaluating MotionBlur is advancing the geometry and interpolating the tweens, but can't 'see' that the Xpresso ties the sphere to the clones it is re-rendering in different - blurred - positions. So the sphere very visibly stays put suddenly, and no longer seems to be stuck to the clones - it's really noticeable if you render from 0-75, around frame 40 it just visibly stops moving the sphere anymore and geometry intersects.

    This seems like a bug, to me, unless there is a workaround...The cached mograph should definitely be letting the renderer know that whatever it is blurring needs to pull the sphere with it, but it's like the motion-blur rendering cannot evaluate the Xpresso...You can clearly see how stupid the result is, considering the sphere is constrained to the surface of that clone 🤔

    Dunno. How do I try this alembic idea, can you elaborate a bit? I don't see how this is solveable otherwise, unless I can somehow get the renderer to recognise the sphere as part of the cloner

    REF NO MoBlur 50.tif REF MoBlur 49.tif REF NO MoBlur 49.tif REF MoBlur 50.tif

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  • Strangest thing:
    Even if I bake the Xpresso-animated sphere in the Timeline, and disable or delete the Xpresso from the Object Manager, so there's only keyframes, the renderer still leaves the sphere static while going buckwild with the clones, which are settling down in their animation at this point!

    It's absurd, the motionblur is being selective with geometry that is moving together in the viewport and observing the keyframes, should be dealt with identically by the renderer. I'll see if changing to a custom Density on the sphere helps...but dynamics are not being used.

    And motion blur MAHOOSIVELY changes what is going on in the viewport without it.


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  • The real kicker here is that without the bake on the Mograph, it works just fine! 🤣

    That's not much good if you're using a render farm for the rendering though, is it?!



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    Just found this in the Help Files, I think it's the culprit...

    Spring (Delay Effector)

    As the name suggests, the clones will behave as though they have springs between them, resulting in slight residual oscillation. Over-oscillation can also occur. Large values will increase residual oscillation, i.e., the larger the value, the softer the springs.

    Problems may be encountered when using this Effector in conjunction with Sub-Frame Motion Blur (see Post Effects in your Cinema 4D reference manual).

    I guess they know about it already, and it's not just SFMB in Standard, it's Physical too...

    At least I can leave it alone and find a workaround.

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  • Haha!


    What with a GLOBAL PANDEMIC giving us all a chance to seriously do the stuff that usually is just not viable, I went deep into this :)

    Let me just say, that

    On 3/24/2020 at 1:10 PM, Havealot said:

    As a last resort you can try caching both the sphere and the cloner with alembic.


    It is the ONLY thing that works, trust me on this...

    I copied the cloner, same effectors, swapped for the sphere, used mograph selection to have only the relevant sphere in the matrix visible, and no joy.

    So I used a shader effector on THE SAME CLONER to isolate a single sphere using the 'Sort' mode instead of default 'Iterate', with a shader that was just a tiny white square in a big black square (made in PS) with the black area being planes and the white area being the sphere, all the effectors from the same cloner, etc...and the renderer still could not parse it correctly,

    Bake the cloner to an alembic, and enjoy your DOF and Motion Blur!


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