• Adobe After Effects Expressions

  Continuous bounce

  Posted by Kenji Takahashi on June 29, 2020 at 11:36 pm

  Hi I need help with the “famous” bounce expression. It`s interesting problem and I`m scratched out.

  Because frequence and decay are low ( I need it to be extra elastic) it only work for two keyframes.
  On keyframe 3 it snaps in its value and sometimes on keyframe 4, 5, 7, 9.. depending on the nearest key index I presume
  I`m trying valueAtTime but I`m limited with knowledge.

  I need my keyframes not to be precise but relative to previous inherited velocity.

  Thnx

  freq = 0.5;
decay = 1;

  n = 0;
if (numKeys > 0){
n = nearestKey(time).index;
if (key(n).time > time) n--;
}
if (n > 0){
t = time - key(n).time;
amp = velocityAtTime(key(n).time - .001);
w = freq*Math.PI*2;
value + amp*(Math.sin(t*w)/Math.exp(decay*t)/w);
}else
value

  Kenji Takahashi replied 6 years, 3 months ago 2 Members · 4 Replies
• 4 Replies

• 

  Dan Ebberts

  June 30, 2020 at 6:32 am

  See what this version does for you:

  
freq = 0.5;
decay = 1;
val = value
n = 0;
if (numKeys > 0){
n = nearestKey(time).index;
if (key(n).time > time) n--;
}
if (n > 1){
amp = velocityAtTime(key(n).time - .001);
w = freq*Math.PI*2;
for (i = 2; i <= n; i++){
t = Math.min(time - key(i).time,10/decay);
amp = velocityAtTime(key(i).time - .001);
val += amp*(Math.sin(t*w)/Math.exp(decay*t)/w);
}
}
val


  Dan
• 

  Kenji Takahashi

  June 30, 2020 at 11:33 am

  Absolutely beautiful, thank you Dan,
  you sir are a gentleman and a scholar!

  It will take hours to see what you did there 🙂
• 

  Dan Ebberts

  June 30, 2020 at 12:47 pm

  This is slightly better:

  
freq = 0.5;
decay = 1;
val = value
n = 0;
if (numKeys > 0){
n = nearestKey(time).index;
if (key(n).time > time) n--;
}
if (n > 1){
w = freq*Math.PI*2;
for (i = 2; i <= n; i++){
t = time - key(i).time;
if (t > 10/decay) continue;
amp = velocityAtTime(key(i).time - .001);
val += amp*(Math.sin(t*w)/Math.exp(decay*t)/w);
}
}
val


  Dan
• 

  Kenji Takahashi

  June 30, 2020 at 1:42 pm

  Yeah this one is cleaner.

  I was actually looking for solution to do this.

  

  I call it inertial animation. (or Ice animation ☺ )
  Basically with the tweak in frequency and decay I can make inertia in movement without null parenting, with fever keyframes and without tweaks to keyframe velocity.
  Example above was done with the code below and just easing first keyframe of movement. (animation must be done in linear fashion, forward, keyframe by keyframe. Just like pushing hockey puck on ice)

  Once again thanks Dan!

  freq = 0.001;
decay = 0.6;
val = value
n = 0;
if (numKeys > 0){
n = nearestKey(time).index;
if (key(n).time > time) n--;
}
if (n > 1){
w = freq*Math.PI*2;
for (i = 2; i <= n; i++){
t = time - key(i).time;
if (t > 10/decay) continue;
amp = velocityAtTime(key(i).time - .001);
val += amp*(Math.sin(t*w)/Math.exp(decay*t)/w);
}
}
val

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