Detecting a collision with expressions

Question

I have a layer moving along the X-axis. I have a shape layer with a simple stroke and trim paths that has the starting point of the stroke on the same X-axis. When the moving layer (m) reaches the same X value, I want the stroke to move up.  This simple expression pops the line up to 100%
 
m = thisComp.layer("Mover").position;
r = position;

if (m[0] < r[0] || m[0] > r[0] + 60)
	y = 0;
else
	y = 100;
 
There are no keyframes at the time of the collision, so using time in an ease method is not working for me. 
 
Is there some way to come up with an interpolation method that says
 
when m = r increase the value of y so that when m = r + 30, y == 100;
then as m moves from r+30 to r + 60, y changes from 100 to 0
 
If I had a keyframe where the collision occurs, it would be easy to use valueAtTime for the keyframe to create the growing and falling stroke. I can't figure out how to make it happen without a keyframe.
 
Any suggestions would be appreciated.
 
This could also be helpful in animating a countdown so as the numbers go from 10 to zero a line would grow and shrink instead of just blinking when each number is reached.

Dan Ebberts · Accepted Answer

I'm having trouble picturing what you're trying to do and how it's affected by the number of points in the star. I think a more detailed description would help.

This is one idea. It assumes your value for Points only jumps in whole number increments. The expression checks to see when it last changed and when it next changes and uses the time in between those changes to animate from 0 to 100. I have no idea if that's what you're looking for, but it might give you some ideas:

n = content("Polystar 1").content("Polystar Path 1").points;
tMin = null;
tMax = null;
t = time - thisComp.frameDuration;
while(t >= inPoint){
  if (n.valueAtTime(t) != n){
    tMin = t+thisComp.frameDuration;
    break;
  }
  t -= thisComp.frameDuration;
}
t = time + thisComp.frameDuration;
while(t <= outPoint){
  if (n.valueAtTime(t) != n){
    tMax = t-thisComp.frameDuration;
    break;
  }
  t += thisComp.frameDuration;
}
if (tMin != null && tMax != null){
  ease(time,tMin,tMax,0,100);
}else{
  0;
}

Dan Ebberts · Answer

Maybe something like this:m = thisComp.layer("Mover").transform.position[0];r = position[0];m < r + 30 ? ease(m,r,r+30,0,100) : ease(m,r+30,r+60,100,0)

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