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A
AnyON
Inspiring
June 18, 2023
Question

About expressions. *Rotate layer by two layers position*

  • June 18, 2023
  • 2 replies
  • 877 views
Hi all...
 Maybe
who will help in writing the 
expression for the following situation.
The composition layer has 2 position 
keys. I want to add the following
 behavior for the rotation property.
 In the initial position key, the rotation 
value is 0.0, in the final position key, 
the rotation is also 0.0, but 
in the interval between these position keys, 
there is a deviation, by a certain amount, 
for our example, let this value be 90.0 degrees. 
And I would also like to control the position of the 
peak relative to the position keys, and the tangents 
of the approach and to this value of 90.0

 

    This topic has been closed for replies.

    2 replies

    R
    Community Expert
    Rick GerardCommunity Expert
    Community Expert
    June 18, 2023

    If you want to use the position of a keyframe in the timeline to control the rotation of a layer, use two ease or linear interpolation method and the time between the keyframes and then set the ratio between the two times and the maximum angle. 

     

    Let's say that if the time between keyframes is greater than 1 second, the layer does not rotate, but if the time is less than one second, the layer would rotate 180º and back again. That expression would look like this:

     

    t = time;
minTime = 1;
tStart = position.key(1).time;
tEnd = position.key(2).time;
tMiddle = tEnd - tStart / 2;
restAngle = 0;
maxAngle = 180;
if (tMiddle - tStart < tEnd - tStart/2){
	rStart = ease(t, tStart, tMiddle, restAngle, maxAngle);
}
if (tMiddle - tEnd < tEnd - tStart/2){
	rEnd = ease(t, tMiddle, tEnd, maxAngle, restAngle);
}
if (tEnd - tStart < minTime){
	r = rStart + rEnd - 180;
}

else{
	r = 0;
}

     

    If you wanted the time between keyframes to generate a minimum and maximum angle. you just need to do the math. 

     

    To create an expression that does exactly what you want it to do would require you to give us the exact parameters. For example, if the time between keyframes is one second, then the layer rotates from 0º to 90º, but if the time between keyframes is two seconds, the layer rotates between 0º and 180º.

     

    Maybe that explanation will give you something to build on. 

      A
      AnyONAuthor
      Inspiring
      June 18, 2023

      Thank you for your attention to my question Rick, I sketched something similar in the example you gave, but I did not know that in the if else condition, you can use an expression like

      rStart = ease(t, tStart, tMiddle, restAngle, maxAngle);

      In that case it's possible...

       

      R
      Community Expert
      Rick GerardCommunity Expert
      Community Expert
      June 18, 2023

      I think I made a mistake calculating time in that example, so the move is not centered. There is probably another error there too.

       

      If I get a chance later, I'll try and fix it by opening up AE and fiddling with the math.

       

      EDIT:I fixed the expression to center the move. It now looks like this:

      t = time;
minTime = 4;
tStart = position.key(1).time;
tEnd = position.key(2).time;
tMiddle = (tEnd - tStart) / 2;
restAngle = 0;
maxAngle = 180;
if (tMiddle - tStart < tEnd - tStart){
	rStart = ease(t, tStart, tStart + tMiddle, restAngle, maxAngle);
}
if (tMiddle - tEnd < tEnd - tStart){
	rEnd = ease(t, tMiddle, tEnd, maxAngle, restAngle);
}
if (tEnd - tStart < minTime){
	r = (rStart + rEnd);
}

else{
	r = 0;
}
r - 180;

      That expression should give you a clockwise rotation from zero to 180º and back to zero any time the position keyframes are less than four seconds apart. 

        ShiveringCactus
        Community Expert
        ShiveringCactusCommunity Expert
        Community Expert
        June 18, 2023

        Sounds like you're describing wanting to keyframe a wiggle, so that you can control when it's in use.

        I made a tutorial a few years back to explain how:

        https://youtu.be/SqVZcGEZVp4

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