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bentway

Animate sweep nurb end based on null?

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Hi, all--I'm returning to C4D after a while away and am trying to figure out how I can animate the end growth of a seep nurb based on the position of a null moving on an identical path (but not the same path, due to its creation).

 

The source is mocap. I PSR-constrained nulls to joints for which I want to generate trails (to be used for text alignment, eventuallly). I baked the nulls and converted those Position tracks to splines.

 

I can use those splines for text alignment or sweeping with arbitrary end-growth animation , easy, but what I want to do is have the end point of the sweep to move based on the movement of one of the nulls (baked or not). (I'm going to do this (1) to create a boolean to reveal what's aligned to the spline, and (2) see the splines drawn on while previs-ing.) They're obviously following an identical path, but the motion timing is irregular because of mocap, so I can't simply align them to the spline path and animate beginning/end points.

 

All my Googling has come to naught.

 

I figured that since there is a spline vertex per frame, animating the growth (with a linear tangent) from 0 - 100 along the frame range would match up, due to quicker frame movements consequently having greater distance between corresponding vertices, but this isn't working like I'd hoped.

 

I've been away a while, but XPresso/expressions don't scare me, and I assume the answer is there. Perhaps identifying the world space coordinates of the "driver" null that will drive the end growth, applying those coordinates to the spline, and then determining at what percentage of the spline that coordinate appears? Or could I align another null to the spline and simultaneously P-constrain it to the source null, so it follows the source but slides along the spline, and I can use that align-to-spline percentage to drive the sweep end?

 

Thanks so much for any help!

 

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