Source: recognizers/pan.js

/**
 * Pan
 * Recognized when the pointer is down and moved in the allowed direction.
 * @constructor
 * @extends AttrRecognizer
 */
function PanRecognizer() {
    AttrRecognizer.apply(this, arguments);

    this.pX = null;
    this.pY = null;
}

inherit(PanRecognizer, AttrRecognizer, {
    /**
     * @namespace
     * @memberof PanRecognizer
     */
    defaults: {
        event: 'pan',
        threshold: 10,
        pointers: 1,
        direction: DIRECTION_ALL
    },

    getTouchAction: function() {
        var direction = this.options.direction;
        var actions = [];
        if (direction & DIRECTION_HORIZONTAL) {
            actions.push(TOUCH_ACTION_PAN_Y);
        }
        if (direction & DIRECTION_VERTICAL) {
            actions.push(TOUCH_ACTION_PAN_X);
        }
        return actions;
    },

    directionTest: function(input) {
        var options = this.options;
        var hasMoved = true;
        var distance = input.distance;
        var direction = input.direction;
        var x = input.deltaX;
        var y = input.deltaY;

        // lock to axis?
        if (!(direction & options.direction)) {
            if (options.direction & DIRECTION_HORIZONTAL) {
                direction = (x === 0) ? DIRECTION_NONE : (x < 0) ? DIRECTION_LEFT : DIRECTION_RIGHT;
                hasMoved = x != this.pX;
                distance = Math.abs(input.deltaX);
            } else {
                direction = (y === 0) ? DIRECTION_NONE : (y < 0) ? DIRECTION_UP : DIRECTION_DOWN;
                hasMoved = y != this.pY;
                distance = Math.abs(input.deltaY);
            }
        }
        input.direction = direction;
        return hasMoved && distance > options.threshold && direction & options.direction;
    },

    attrTest: function(input) {
        return AttrRecognizer.prototype.attrTest.call(this, input) &&
            (this.state & STATE_BEGAN || (!(this.state & STATE_BEGAN) && this.directionTest(input)));
    },

    emit: function(input) {

        this.pX = input.deltaX;
        this.pY = input.deltaY;

        var direction = directionStr(input.direction);

        if (direction) {
            input.additionalEvent = this.options.event + direction;
        }
        this._super.emit.call(this, input);
    }
});