Shape on motion path - Aftereffects Expression

shapeonmotionpath

seg = Math.floor( Math.max(effect("Segments")("Slider"), 2) );
starttime = effect("Start Time")("Slider");
endtime = effect("End Time")("Slider");
smooth = effect("Smooth")("Checkbox") > 0;

targetlayer = thisComp.layer("Tip");

timemin = Math.min(starttime, endtime);
timemax = Math.max(starttime, endtime);
cv = [];
for(var i = 0; i < seg + 1; i++){
	f = linear(i, 0, seg, timemin, timemax);
	cv.push( fromCompToSurface( targetlayer.toComp( targetlayer.anchorPoint, f ) ) );
}

// quadratic curve bezier approximation.
if(smooth){
	points = [];
	intan = [];
	outtan = [];

	for(var i = 0; i < cv.length; i++){
		if(i == 0){
			points.push(cv[i]);
			intan.push([0,0]);
			outtan.push( (cv[i+1] - cv[i]) * (2 / 3) );
		}else if(i == cv.length-1){
			points.push(cv[i]);
			intan.push( (cv[i-1] - cv[i]) * (2 / 3) );
			outtan.push([0,0]);
		}else{
			pos = cv[i] + div(cv[i+1] - cv[i], 2);
			points.push(pos);
			intan.push( (cv[i] - pos)  * (2 / 3) );
			outtan.push( (cv[i+1] - pos) * (2 / 3) );
		}
	} 
	
	createPath(points, intan, outtan, false); 
}

if(!smooth) createPath(cv, [], [], false);