var lastx = 0;
var lasty = 0;
WorkerScript.onMessage = function(message) {
var ydiff = message.y - lasty;
var xdiff = message.x - lastx;
var total = Math.sqrt(ydiff * ydiff + xdiff * xdiff);
lastx = message.x;
lasty = message.y;
WorkerScript.sendMessage( {xmove: xdiff, ymove: ydiff, move: total} );
}