• Adobe After Effects Expressions

  How to change “beginTime = thisLayer.inPoint” to keyframe or checkbox?

  Posted by Stephen Pickering on March 13, 2013 at 10:54 pm

  Hi there,
  I have a comp which uses the following expression:

  beginTime = thisLayer.inPoint;
if (time < beginTime){
0
}else{
t = time - beginTime;
veloc = [effect("Velocity")("Slider")]*.1;
amplitude = effect("Amplitude")("Slider");
decay = [effect("Decay")("Slider")]*.01;
amplitude*Math.sin(veloc*t)/Math.exp(decay*t) }

  It’s a pendulum expression from Cineblur. I would like however to not have the sway start at the layer’s in point but rather at a keyframe or a “checkbox” I was able to get it to react to a checkbox control(by replacing “thisLayer.inPoint.” But because it has a decay expression it begins decaying right away from “inPoint” even though there is no movements until the checkbox was ticked. So basically if I ticked the box at 5 seconds but it has a 7 second decay it only shows subtle movement for 2 seconds, beginning at 5 seconds. Does that make sense?

  Any ideas?

  Thank you!

  -Stephen

  Stephen Pickering replied 13 years, 5 months ago 2 Members · 4 Replies
• 4 Replies

• 

  Dan Ebberts

  March 13, 2013 at 11:16 pm

  What did you change the first line to? I would think you’d want something like this:

  beginTime = effect(“Checkbox Control”)(“Checkbox”).key(1).time;

  Dan
• 

  Stephen Pickering

  March 14, 2013 at 3:54 am

  I believe I had changed it to something like:

  beginTime = effect(“Checkbox Control”)(“Checkbox”);

  But it looks like your expression works. Thank you very much. Can you tell me what the “.key(1).time” does?

  Is there any way to make a checkbox that turns it on again? I’m working on a venetian blinds effect. The expression above is for the “sway” which is the result of the blinds closing. The blinds will open and close multiple times so i would need to repeat this decaying pendulum sway multiple times.

  Thanks Dan!

  -Stephen
• 

  Dan Ebberts

  March 14, 2013 at 4:14 am

  key(1).time gives you the time of the first checkbox keyframe.

  If you want to trigger it at every checkbox keyframe, you could do it like this:

  
cb = effect("Checkbox Control")("Checkbox");

  n = 0;
if (cb.numKeys > 0){
n = cb.nearestKey(time).index;
if (cb.key(n).time > time) n--;
}
if (n == 0){
0;
}else{
t = time - cb.key(n).time;
veloc = effect("Velocity")("Slider")*.1;
amplitude = effect("Amplitude")("Slider");
decay = effect("Decay")("Slider")*.01;
amplitude*Math.sin(veloc*t)/Math.exp(decay*t)
}


  Dan
• 

  Stephen Pickering

  March 14, 2013 at 4:32 am

  Works perfectly Dan, Thanks!

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