Adjust keyframes for constant speed along one axis

[Filip Vandueren]

OK,
a few caveats: this only works for this specific left-to right motion, and given that the motion-path is never tracking back on itself (obviously), so every next keyframe will always have a higher x-value.

This expression will respect the timing of the first and the last keyframe, and linearize the x-motion (constant speed), then do a crude look-up of what Y-value corresponds to the given X according to the motionpath.

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];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]

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

[Filip Vandueren]

OK, let me know.

I just noticed I accidentally pasted the expression-code twice though…

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]

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

[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.