Tracking the top middle of a layer for an expression

[Pansmith28581945rfkl]

Trying to figure out how I would track the topmost middle of an arbitrarily changing shape layer for use in a expression. Said shape layer changes size to fit the size of a textbox.

[Dan Ebberts · Accepted solution]

An expression like this maybe:

L = thisComp.layer("Shape Layer 1");
r = L.sourceRectAtTime(time,false);
L.toComp([r.left+r.width/2,r.top])