Expression to get the current composition's centrepoint
var centre_x = thisComp.width / 2;
var centre_y = thisComp.height / 2;
[centre_x, centre_y];Example usage:
/**
* Apply to the Position property of a layer
* to place it in the centre of a comp
**/
var centre_x = thisComp.width / 2;
var centre_y = thisComp.height / 2;
[centre_x, centre_y];