Expression to detect horizontal axis vector

[Timoishaa]

Hey guys. I'm trying to make an object that is gonna horizontally flip itself when it changes his x axis vector.
 
It basically works, but the problem here that when object isn't moving anywhere or hit keyframe, velocity goes to 0 and because there is no statements that are going to flip object scale, so it goes to the start scale of [100, 100]. Numbers on screenshot is velocity - when it's negative - scale flips from [100, 100] to [-100, 100]
There is expression that I've been using;

if(transform.position.velocity[0]>0){
	[-100, 100]
}else{
	[100,100]
}

What I want to do is the object will remember his last scale number. So if we go from left to right, animation ends - object gonna safe his last scale. What do you think?

[Mylenium]

It's all explained here:

http://www.motionscript.com/articles/speed-control.html

You need to integrate the values in a loop and then make determinations about the values based on some threshold.

Mylenium

[Timoishaa]

Thank you for you reply, Mylenium! That's a beatiful article, I'll be glad to read it later. But I didn't quite understand how I can use this for my purpose? There is too many for me to understand what and where I can use it right now

[Dan Ebberts · Accepted solution]

Something like this, probably:

if(transform.position.velocity[0]>0){
	[-100, 100]
}else if (transform.position.velocity[0]<0){
	[100,100]
}else{
  t = time - thisComp.frameDuration;
  gt = true;
  while(t >= inPoint){
    if (transform.position.velocityAtTime(t)[0] > 0){
      break;
    }else if (transform.position.velocityAtTime(t)[0] < 0){
      gt = false;
      break;
    }
    t -= thisComp.frameDuration
  }
  gt ? [-100,100] : [100,100]
}

[Timoishaa]

It's beautiful!! It works exactly how I wanted! Thank you, Dan.

I don't quite understand what is going on here, but I'll take a closer look 🙂

[Dan Ebberts]

If the horizontal velocity is zero at the current frame, it backs up, frame-by-frame, until it finds the most recent frame where the horizontal velocity was non-zero and uses that value.

[Timoishaa]

Thanks a lot for your time Dan! I figured out how it works 🙂
It's actually pretty simple and clever when I started to realise how the whole script works