Inertial decay of position

[Todd Kopriva]

This script makes such things easy:
https://aescripts.com/ease-and-wizz/

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Todd Kopriva, Adobe Systems Incorporated
After Effects quality engineering
After Effects team blog
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[Navarro Parker]

Thanks Todd. Yeah, I’ve been using E&W for years. Not exactly what I’m asking for.

[Dan Ebberts]

I’ve been thinking about this off and on, and it turns out that it’s trickier than it seems. But I think I’ve got something that works if you’re willing to accept a sine ease. This assumes you have two keyframes and the ease will be applied after the second keyframe so that the overshoot ease is finished by the duration defined by variable frames:


frames = 15; // overshoot frames

if (numKeys == 2){
t2 = key(2).time;
if (time < t2){
value
}else{
ot = framesToTime(frames);
freq = 1/(4*ot);
t = Math.min(ot,time-t2)
amp = velocityAtTime(t2 - .001);
w = freq*Math.PI*2;
valueAtTime(t2) + amp*Math.sin(t*w)/w;
}
}else
value


Dan

[Navarro Parker]

Thanks Dan. Yeah, this behaves differently than I imagine. That sine falloff is a lot “slippery-er” than I expect. Layers just want to slider off my page with the smallest push. Reducing the overshoot frames makes it brake unnaturally.

Hmmmm… I guess I want a more graceful braking. I’m scrolling through my iPod playlist. I can give a quick flick, and it’ll scroll very fast, but then gently brake to a complete stop. Fiddling with your expression a little, I can’t seem to get short fast motion with that perfect de-acceleration.

[Dan Ebberts]

I don’t know if this is headed in the right direction, but here’s another version with an exponential ease. Variable damp adjusts how fast it slows down:


damp = 5;

if (numKeys == 2){
t2 = key(2).time;
if (time < t2){
value
}else{
t = time - t2;
amp = velocityAtTime(t2 - .001);
valueAtTime(t2) + amp*(1-1/Math.exp(t*damp))/damp
}
}else
value


Dan

[Navarro Parker]

That’s fantastic! Thank you very much!

[Chris Thomas]

I know this has been closed for quite some time, but I thought I’d try a quick follow-up.

I’ve been using this script for a few years for UI/UX work and it’s absolutely wonderful. However I’m desperate for a version that allows you to add multiple instances of this movement on a single object. As it stands, you must add a parented null (or similar) every time you want to scroll again. As I’m sometimes doing this 10 or more times, it gets very complicated very quickly.

Would love to know if there’s a way to adapt this!