Not sure I understand 100%, but it sounds like you would use a slider to control the interpolation between the layers actual position, and a minimum or maximum amount.  So if you have a slider called "Amount 0-100" your position expression would be:

p=transform.position;

x=p[0];y=p[1];

minx=0;miny=0;

slider=effect("Amount 0-100")("Slider");

x=linear(slider,0,100,minx,x);

y=linear(slider,0,100,miny,y);

[x,y]

Is this what you mean? 

-Chris

On 12/07/2014, at 10:07 AM, Teddy Gage <AE-List@media-motion.tv> wrote:

Not even sure this is possible. But say you have an object on a motion path with hundreds of keys (not able to be reproduced by expressions). Would it be possible to put an expression on a slider linked to those keyframes to dynamically control, say, the absolute minimum and maximum values the object travels on the x axis? 

Sort of like scaling the entire motion path of keys in one or all directions, but tying that to a slider, so that when the slider is at 0, there is no motion. ie it clamps all values to 0.

There is probably an easier way to do this but I was wondering if this it was possible like this. Thanks,

-TG

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VFX & Motion Graphic Artist
teddygage dot com