Tracer Substeps for Motion Blur

[deal-blind]

Hi, I hope this is not a stupid question that has been answered elsewhere, couldn't find it. I'm a semi-noob in C4D.

I am building a setup where a tracer object is tracing cloned objects that are moving around. Said tracer is in a sweep nurb so the objects leave trails.
So far so awesome.

As soon as I enable Motion Blur in Redshift, the already traced splines begin to shift around - I could trace this problem back to the Tracer Objects Intermediate Points. The Tracers Splines change every frame since it grows and it seems a lot of the already traced points change to accomodate for the new shape.

So the only option I found to enable Motion Blur is to set the Tracer Objects type to linear with no intermediate points. But that produces clunky traced splines.

My workaround right now is to change the framerate from 25 to 200 since this produces 8 times the points in the traced paths and render only every 8th frame while still having the Motion Blur on 1/50th second.

It works but is a bit annoying. Is there any way to make the Tracer Object create these subframe steps without doing this workaround?

I hope this is the appropriate place to ask this and appreciate any help.

[Dr. Sassi]

Hi deal-blind,

There are no stupid questions, perhaps stupid replies…; in other words, please feel free to ask. I will do my best to find an answer.

Thanks for the question and the details.

You did not provide many details about your settings or the used render engine.

Could you please copy the object that created the trace spline and have rendering settings as in the file you encountered the problem? That should be very small and possible to be added as a c4d file here. If the camera is animated, please include this as well.

What you can do, as a workaround, is take the 200 frame set up to write out an Amebic file for the Spline. Then, switch to the render settings you would like to have. For the Spline Alembic, set the speed to 800%.

Another point would be, if you are in Redshift 3D, to check if the Motion Blur Deformation settings work. Again, without a project file, I can't tell.

All the best

[deal-blind]

Hi Dr. Sassi,

many thanks for your reply. I think I've found a solution with your help. (I'm working in Redshift by the way).

One more about the problem - as far as I can tell and if I understand everything correctly - the growing tracers have a different number of points/vertices every frame since they grow with the motion of another object. As soon as I set up Motion Blur in Redshift, the shapes get all whacky - wild guess would be that vertice A on frame 1 is on another point on the spline on frame 2. Which would mean that the RS Motion Blur calculates the movement between those two (as it should) but it looks super strange and makes wild shapes. This happens even if deformation blur is off.

With your tip - which was worth gold, thanks again - the motion blur works as intended as long as deformation blur is set to off. I guess that the alembic file stores fixed positions and changes them from frame to frame without interpolating between them, while the tracer object is able to generate in-betweens which the RS Motion Blur pulls from it although they are gibberish. So - that's a great system for just camera motion blur. BUT, I still had some Macro-Setups where the growing splines are visible and which looked really jaggy without motion blur.

For that problem I'm using another workaround right now, which seems to work. I take the baked alembic-tracer out of my sweep-setup and instead use a Spline-Wrap deformer on a cylinder that uses the alembic as spline source. And while animating the end-point, it stretches the cylinder (which has a crazy amount of height segments) along the alembic. It's a bit of a workaround and sadly the percentage of the baked alembic spline-wrap doesn't match the percentage of the original animation, so I have to animate it frame by frame. BUT since I don't have any textures and just need glowing light streaks, the motion blur works as intended.

I hope that makes sense. Thanks again for your help

[Dr. Sassi]

Hi deal-blind,

You're very welcome.

Thanks for the reply and the patience with this
Perhaps try a Spline Wrap with a fixed number of points.

The Deformation Blur works only with consistent topologies. Hence I asked about a file and the settings, while not knowing which render you use. I assume that when it would have been Redshift, you would have seen the alert about insistent Topology. Hence I assumed you do not use Redshift. But as usual, guessing is not my favorite part; Project files are.

The easiest, yet most messy, workaround would be to set the play head to single. Then let's run the animation one time through, and while the tracer is active, use the Current State To Object. This gives you a single path, and the Spline Wrap has worked here with Redshift.

If you would like a faster way to get the path of an animated object as a Spline, go to Timeline> F-Curve> Function> Position Track To Spline.

All the best

Dr. Sassi

[deal-blind]

Hi Dr. Sassi,

awesome - that cuts a few steps in between.

Thanks again!

[Dr. Sassi]

You're very welcome, deal-blinet.

Have a great long weekend