Hello! Is there a directional blur that can be controlled with a null? E.g. I have a background plate and a null tracked from the camera motions of the plate. I then have a cel animated layer to which I would like to "copy" the same amount and direction of blur from the bg plate.
If the elements were 3d it would be easy to render a motion vector pass and use e.g. RSMB, but how would something similar be done in this case?
Well, determining the direction only requires a simple "targeting expression" with Math.atan2() applied to the respective parameter in Directional Blur. A simple web search can turn up enough ecxamples or even just browsing this forum. I answered a similar question only a few days ago. Determining the amount would be more tricky, as there is no causal relation and in fact it may look rather jittery, so I'd simply animate it by hand. Otherwise it would be quite some complex math determining the difference of the resulting velocity vector between two sample points at different times using valueAtTime() similar how you align items to paths by looking ahead or looking back on their trail.
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