[James Hamilton]

In case anyone else needs a solution to this, enter the below code into the Position property of your keyframed object.

Many thanks to the brain of Filip Vandueren who came up
with this solution.

t1= key(1).time;
t2= key(numKeys).time;

x1=key(1).value[0];
x2=key(numKeys).value[0];

linear_x=linear(time, t1, t2, x1, x2);

precision = 3; // make this higher (16) if you need Motion blur
fd = thisComp.frameDuration/precision;

y=key(1).value[1];

for (t=t1; !(t>t2); t+=fd) {
v=valueAtTime(t);
if (v[0]>=linear_x) {
y=v[1];
break;
}
}

[linear_x,y];

[James Hamilton]

It works perfectly! This really helps me out, thank you so much.
Last time I coded was Basic language at school but this has renewed my interest.

[James Hamilton]

Thanks for pointing that out.
It’s shortened length makes it a little less scary at least…

[James Hamilton]

Wow, thanks. That is complex!
I can’t try it right now but will later today…

[James Hamilton]

You might be thinking along the right line…

But I have 5 more graphs to make and I believe a solution exists that could avoid all the key framing, and if a solution is found it’s something that I think could be helpful for people in other projects.

If there was a way to automatically create keyframes at the intersection of two objects (the vertical line and the curve) that would be ideal.

Or, if the moving object could automatically reference the Y value of the curve, but the X value of the moving line.

[James Hamilton]

Thanks for suggesting your idea. However the dot does need to be a shape object as I need it to look a particular way and a light sweep will not allow for that.

I do understand what you are saying about the fact that the object is technically travelling at a constant speed already, in terms of its XY axes.

However the speed in relation to a particular axis varies. It’s an interesting problem, and deceptively complex. And I have no idea how to solve it.