Leaflet/src/dom/Draggable.js

/*
 * L.Draggable allows you to add dragging capabilities to any element. Supports mobile devices too.
 */

L.Draggable = L.Evented.extend({

	statics: {
		START: L.Browser.touch ? ['touchstart', 'mousedown'] : ['mousedown'],
		END: {
			mousedown: 'mouseup',
			touchstart: 'touchend',
			pointerdown: 'touchend',
			MSPointerDown: 'touchend'
		},
		MOVE: {
			mousedown: 'mousemove',
			touchstart: 'touchmove',
			pointerdown: 'touchmove',
			MSPointerDown: 'touchmove'
		}
	},

	initialize: function (element, dragStartTarget) {
		this._element = element;
		this._dragStartTarget = dragStartTarget || element;
	},

	enable: function () {
		if (this._enabled) { return; }

		for (var i = L.Draggable.START.length - 1; i >= 0; i--) {
			L.DomEvent.on(this._dragStartTarget, L.Draggable.START[i], this._onDown, this);
		}

		this._enabled = true;
	},

	disable: function () {
		if (!this._enabled) { return; }

		for (var i = L.Draggable.START.length - 1; i >= 0; i--) {
			L.DomEvent.off(this._dragStartTarget, L.Draggable.START[i], this._onDown, this);
		}

		this._enabled = false;
		this._moved = false;
	},

	_onDown: function (e) {
		this._moved = false;

		if (e.shiftKey || ((e.which !== 1) && (e.button !== 1) && !e.touches)) { return; }

		L.DomEvent.stopPropagation(e);

		if (L.Draggable._disabled) { return; }

		L.DomUtil.disableImageDrag();
		L.DomUtil.disableTextSelection();

		if (this._moving) { return; }

		var first = e.touches ? e.touches[0] : e;

		this._startPoint = new L.Point(first.clientX, first.clientY);
		this._startPos = this._newPos = L.DomUtil.getPosition(this._element);

		L.DomEvent
		    .on(document, L.Draggable.MOVE[e.type], this._onMove, this)
		    .on(document, L.Draggable.END[e.type], this._onUp, this);
	},

	_onMove: function (e) {
		if (e.touches && e.touches.length > 1) {
			this._moved = true;
			return;
		}

		var first = (e.touches && e.touches.length === 1 ? e.touches[0] : e),
		    newPoint = new L.Point(first.clientX, first.clientY),
		    offset = newPoint.subtract(this._startPoint);

		if (!offset.x && !offset.y) { return; }

		L.DomEvent.preventDefault(e);

		if (!this._moved) {
			this.fire('dragstart');

			this._moved = true;
			this._startPos = L.DomUtil.getPosition(this._element).subtract(offset);

			L.DomUtil.addClass(document.body, 'leaflet-dragging');
			L.DomUtil.addClass((e.target || e.srcElement), 'leaflet-drag-target');
		}

		this._newPos = this._startPos.add(offset);
		this._moving = true;

		L.Util.cancelAnimFrame(this._animRequest);
		this._animRequest = L.Util.requestAnimFrame(this._updatePosition, this, true, this._dragStartTarget);
	},

	_updatePosition: function () {
		this.fire('predrag');
		L.DomUtil.setPosition(this._element, this._newPos);
		this.fire('drag');
	},

	_onUp: function (e) {
		L.DomUtil.removeClass(document.body, 'leaflet-dragging');
		L.DomUtil.removeClass((e.target || e.srcElement), 'leaflet-drag-target');

		for (var i in L.Draggable.MOVE) {
			L.DomEvent
			    .off(document, L.Draggable.MOVE[i], this._onMove)
			    .off(document, L.Draggable.END[i], this._onUp);
		}

		L.DomUtil.enableImageDrag();
		L.DomUtil.enableTextSelection();

		if (this._moved && this._moving) {
			// ensure drag is not fired after dragend
			L.Util.cancelAnimFrame(this._animRequest);

			this.fire('dragend', {
				distance: this._newPos.distanceTo(this._startPos)
			});
		}

		this._moving = false;
	}
});