code: function w3cTouchConvert(touchList) {
        var canvasOffset = display._getCanvasOffset();
        var tList = [];
        for (var i = 0; i < touchList.length; i++) {
           var touchEvent = touchList.item(i);
           tList.push({
              identifier: touchEvent.identifier,
              pos: [touchEvent.clientX - canvasOffset[0], touchEvent.clientY - canvasOffset[1]]
           });
        }
        return tList;
     }
docs: convert a w3c touch event into gamejs event