• Adobe After Effects Expressions

  How to start an animation on event?

  Posted by Taras Kosmachuk on November 14, 2013 at 7:28 pm

  Hi!
  I have a layer with an animation and a null object. I need to set the animation to start when the null passes anchor point of the layer on x axis…
  Here’s the overall algorithm that I’m using but the problem is that I don’t know how to find the time when above condition happens!

  nullObject = thisComp.layer(“null”);

  nullObject = nullObject.toWorld(nullObject.anchorPoint);
  layPos = thisLayer.toWorld(thisLayer.anchorPoint);
  trackValue = layPos[0]-nullObject[0];

  if (trackValue <= 0) {
  t = ??? // algorithm to find time…
  } else {
  t = time;
  }

  value=value.atTime(t);

  Can anyone help me with this?
  Thanks in advance!

  Taras Kosmachuk replied 12 years, 6 months ago 2 Members · 4 Replies
• 4 Replies

• 

  Dan Ebberts

  November 14, 2013 at 8:47 pm

  Your expression needs to start at the current frame and go back in time frame-by-frame, until you find the most recent frame where the null’s x went from being less than the target x to more than the target x. Then subtract the time of that frame from the current time to determine how long your animation has been running.

  It’s really just a threshold detector along the lines of this beat detector:

  https://www.motionscript.com/design-guide/audio-trigger.html

  Dan
• 

  Taras Kosmachuk

  November 19, 2013 at 1:07 am

  Hi Dan! Thanks for helping me out!

  I’ve adapted your expression to my needs and it seems to be correct, it should return time when layer x position is less or equal to null x position… But ae returns an error:

  “Function trackValue.valueAtTime is undefined”

  What am I doing wrong?

  goalNull = thisComp.layer("null");

  goalPos = goalNull.toWorld(goalNull.anchorPoint);
  layPos = thisLayer.toWorld(thisLayer.anchorPoint);
  trackValue = layPos[0]-goalPos[0];

  check = false;
for (f = 0; f <= timeToFrames(); f++){
t = framesToTime(f);
if (trackValue.valueAtTime(t) <= 0 ){
check = true;
break;
}
}
if (check)
t;
else
time;
• 

  Dan Ebberts

  November 19, 2013 at 1:57 am

  I haven’t tested this, but I think you need to move some of your code inside the loop and use the time parameter of toWorld() to get the time-appropriate values:

  
goalNull = thisComp.layer("null");
check = false;
for (f = 0; f <= timeToFrames(); f++){
t = framesToTime(f);
goalPos = goalNull.toWorld(goalNull.anchorPoint,t);
layPos = toWorld(anchorPoint,t);
trackValue = layPos[0]-goalPos[0];
if (trackValue <= 0 ){
check = true;
break;
}
}
if (check) t else time;


  Dan
• 

  Taras Kosmachuk

  November 19, 2013 at 2:49 am

  It works just perfect! Thanks a lot!

Reply to this Discussion! Login or Sign Up