Auto vertical align comp

[Filip Vandueren]

Hi Benjamin,

give this expression to the layer’s position:

[value[0],thisComp.height/2];

and this expression to the layer’s anchorPoint:

posterizeTime(0);
l=thisLayer;
// upperbound:
for (i=0; i<l.height; i++) {
	samp = l.sampleImage([l.width/2, i+0.5], radius = [l.width, .5], postEffect = true, t = time);
	if (samp[3]!=0) break;
}
upper = i;
// lowerbound:
for (i=height; i>upper; i--) {
	samp = l.sampleImage([l.width/2, i-0.5], radius = [l.width, .5], postEffect = true, t = time);
	if (samp[3]!=0) break;
}
lower = i;
[value[0], (upper+lower)/2];

Mind you: it doesn’t work if your text and images fall outside of the bounds of the original Precomp, let me know if that would be a problem.

[Benjamin Chellaram]

Thank you!

This works, but it looks like it’s constantly calculating making after effects halting and sometimes crashing. There are animations going on inside the comp, but only the first few frames before the animation stops/”lands”. Any workarounds for this?

[Filip Vandueren]

Strange. posterizeTime(0) should take care of this.

Mind you: this does mean that it only looks at what’s in the precomp at time=0, it theres’ nothing there yet…

You can change the two t=time mentions to something like t=2 to look at the vertical boundingbox at the 2 second mark of the precomp.

Other than that, I can’t replicate the halting/crashing behaviour ?

[Filip Vandueren]

It probably has to do with using sampleImage() on a collapsed layer, and the result of the sampleImage is that the layer changes, so the result of sampleImage() would change too, a sort of circular error.

The easiest way around that would be to have a 2nd invisible copy of the precomp which doesn’t have any expressions applied, and sample that one.

so line 2 becomes:

l=thisComp.layer("Comp 2 copy"); // not this layer but a copy !

[Benjamin Chellaram]

Hmm, so it works but it makes ae reeeally slow.
So what I want to sample is the precomp at 2s / frame 50 (comp is set to 25fps) and make it auto-center vertically from that point in time. Just once, I dont want it to calculate from start to finish.

I have used your expression and changed line 2 and changed t=2. I have also freeze framed the invisible copy, but it still makes everything really slow.

Maybe this is not doable?

[Tomas Bumbulevičius]

While I haven’t tried this specific approach Filip, I do recall in the past that posterizeTime (as well as making comp 1frame long for calculation purposes only) doesn’t reliably work in all cases.

I have faced situations where it seems that no further calculations might be needed, but everything hanged on to a close-to-freeze situations, due to calculations heaviness on every frame. Thus, I think Benjamin is experiencing exactly the same scenario.

[Benjamin Chellaram]

Did you ever find a workaround or a fix for this, Tomas? 🙂