use with http://sketch.paperjs.org

drawing-paperjs

function smoother(path) {
    var geometric = false;
    for (var factor=0.1; factor < 4.0; factor += 0.1) {
      var np = path.clone()
      np.smooth({type: geometric ? 'geometric' : 'catmull-rom', factor: factor})    
      np.position.y += factor * 10
    }
    
}


function onMouseDown(event) {
	// The mouse was clicked, so let's put a newly created Path into
	// myPath, give it the color black and add the location as the
	// path's first segment.
	project.clear()
	myPath = new Path();
	myPath.strokeColor = 'black';
	myPath.add(event.point);
}

function onMouseDrag(event) {
	myPath.add(event.point);
}

function onMouseUp(event) {
	// The mouse was released, so we add the new location as the end
	// segment of the line.
	myPath.add(event.point);
    myPath.simplify();
    myPath.simplify();

	smoother(myPath)
	myPath.remove();
}

use this in http://sketch.paperjs.org