Opacity jumps to a higher starting point than defined in the linear() expression

[Hauke Sterner]

Hello all!

I’m fairly new to expressions and I have a problem with the following:
L is a static circle that just fades in.
M is the same circle, but it moves across the composition (only x-position).
L is supposed to fade in once M hits the x-position of L.

This is my expression:

L = thisComp.layer(“Punkt”);
M = thisComp.layer(“Punkt_Maske”);

if (M.transform.position[0] >= L.transform.position[0]) {
L.transform.opacity = linear(time, 0, 33);
} else {
0;
}

This expression kind of works, but the opacity of L does not start at 0 like stated in linear(), but jumps to a higher percentage and continues to 33%.

Can somebody tell me what I’m doing wrong?

Thanks! 🙂

[Dan Ebberts]

Your expression needs to calculate how long ago the trigger event happened. Also, you didn’t mention how long the fade in should take, so I just set it to .5 seconds:

L = thisComp.layer("Punkt");
M = thisComp.layer("Punkt_Maske");
fadeDur = .5;
if (M.transform.position[0] >= L.transform.position[0]) {
  t = time - thisComp.frameDuration;
  while (M.transform.position.valueAtTime(t)[0] >= L.transform.position[0]){
    t -= thisComp.frameDuration;
  }
  linear(time-t,0,fadeDur,0,33);
} else {
  0;
}

[Hauke Sterner]

Hi Dan,

thank you very much! It works like a charm! 🙂