core.js

//function(template, UiClass, items, options)

var self = this;

/**
 * Static vars, don't change unless you know what you're doing.
 */
var DOUBLE_TAP_RADIUS = 25, 
	NUM_HOLDERS = 3;

/**
 * Options
 */
var _options = {
	allowPanToNext:true,
	spacing: 0.12,
	bgOpacity: 1,
	mouseUsed: false,
	loop: true,
	pinchToClose: true,
	closeOnScroll: true,
	closeOnVerticalDrag: true,
	hideAnimationDuration: 333,
	showAnimationDuration: 333,
	showHideOpacity: false,
	focus: true,
	escKey: true,
	arrowKeys: true,
	mainScrollEndFriction: 0.35,
	panEndFriction: 0.35,
	isClickableElement: function(el) {
        return el.tagName === 'A';
    },
    getDoubleTapZoom: function(isMouseClick, item) {
    	if(isMouseClick) {
    		return 1;
    	} else {
    		return item.initialZoomLevel < 0.7 ? 1 : 1.5;
    	}
    },
    maxSpreadZoom: 2,

	// not fully implemented yet
	scaleMode: 'fit', // TODO
	modal: true, // TODO
	alwaysFadeIn: false // TODO
};
framework.extend(_options, options);


/**
 * Private helper variables & functions
 */

var _getEmptyPoint = function() { 
		return {x:0,y:0}; 
	};

var _isOpen,
	_isDestroying,
	_closedByScroll,
	_currentItemIndex,
	_containerStyle,
	_containerShiftIndex,
	_currPanDist = _getEmptyPoint(),
	_startPanOffset = _getEmptyPoint(),
	_panOffset = _getEmptyPoint(),
	_upMoveEvents, // drag move, drag end & drag cancel events array
	_downEvents, // drag start events array
	_globalEventHandlers,
	_viewportSize = {},
	_currZoomLevel,
	_startZoomLevel,
	_translatePrefix,
	_translateSufix,
	_updateSizeInterval,
	_itemsNeedUpdate,
	_currPositionIndex = 0,
	_offset = {},
	_slideSize = _getEmptyPoint(), // size of slide area, including spacing
	_itemHolders,
	_prevItemIndex,
	_indexDiff = 0, // difference of indexes since last content update
	_dragStartEvent,
	_dragMoveEvent,
	_dragEndEvent,
	_dragCancelEvent,
	_transformKey,
	_pointerEventEnabled,
	_isFixedPosition = true,
	_likelyTouchDevice,
	_modules = [],
	_requestAF,
	_cancelAF,
	_initalClassName,
	_initalWindowScrollY,
	_oldIE,
	_currentWindowScrollY,
	_features,
	_windowVisibleSize = {},

	// Registers PhotoSWipe module (History, Controller ...)
	_registerModule = function(name, module) {
		framework.extend(self, module.publicMethods);
		_modules.push(name);
	},

	_getLoopedId = function(index) {
		var numSlides = _getNumItems();
		if(index > numSlides - 1) {
			return index - numSlides;
		} else  if(index < 0) {
			return numSlides + index;
		}
		return index;
	},
	
	// Micro bind/trigger
	_listeners = {},
	_listen = function(name, fn) {
		if(!_listeners[name]) {
			_listeners[name] = [];
		}
		return _listeners[name].push(fn);
	},
	_shout = function(name) {
		var listeners = _listeners[name];

		if(listeners) {
			var args = Array.prototype.slice.call(arguments);
			args.shift();

			for(var i = 0; i < listeners.length; i++) {
				listeners[i].apply(self, args);
			}
		}
	},

	_getCurrentTime = function() {
		return new Date().getTime();
	},
	_applyBgOpacity = function(opacity) {
		_bgOpacity = opacity;
		self.bg.style.opacity = opacity * _options.bgOpacity;
	},
	
	_applyZoomTransform = function(styleObj,x,y,zoom) {
		styleObj[_transformKey] = _translatePrefix + x + 'px, ' + y + 'px' + _translateSufix + ' scale(' + zoom + ')';
	},
	_applyCurrentZoomPan = function() {
		if(_currZoomElementStyle) {
			_applyZoomTransform(_currZoomElementStyle, _panOffset.x, _panOffset.y, _currZoomLevel);
		}
	},
	_applyZoomPanToItem = function(item) {
		if(item.container) {
			_applyZoomTransform(item.container.style, 
								item.initialPosition.x, 
								item.initialPosition.y, 
								item.initialZoomLevel);
		}
	},
	_setTranslateX = function(x, elStyle) {
		elStyle[_transformKey] = _translatePrefix + x + 'px, 0px' + _translateSufix;
	},
	_moveMainScroll = function(x, dragging) {

		if(!_options.loop && dragging) {
			// if of current item during scroll (float)
			var newSlideIndexOffset = _currentItemIndex + (_slideSize.x * _currPositionIndex - x)/_slideSize.x; 
			var delta = Math.round(x - _mainScrollPos.x);

			if( (newSlideIndexOffset < 0 && delta > 0) || 
				(newSlideIndexOffset >= _getNumItems()-1 && delta < 0) ) {
				x = _mainScrollPos.x + delta * _options.mainScrollEndFriction;
			} 
		}
		
		_mainScrollPos.x = x;
		_setTranslateX(x, _containerStyle);
	},
	_calculatePanOffset = function(axis, zoomLevel) {
		var m = _midZoomPoint[axis] - _offset[axis];
		return _startPanOffset[axis] + _currPanDist[axis] + m - m * ( zoomLevel / _startZoomLevel );
	},
	
	_equalizePoints = function(p1, p2) {
		p1.x = p2.x;
		p1.y = p2.y;
		if(p2.id) {
			p1.id = p2.id;
		}
	},
	_roundPoint = function(p) {
		p.x = Math.round(p.x);
		p.y = Math.round(p.y);
	},

	_mouseMoveTimeout = null,
	_onFirstMouseMove = function() {
		// Wait until mouse move event is fired at least twice during 100ms
		// We do this, because some mobile browsers trigger it on touchstart
		if(_mouseMoveTimeout ) { 
			framework.unbind(document, 'mousemove', _onFirstMouseMove);
			framework.addClass(template, 'pswp--has_mouse');
			_options.mouseUsed = true;
			_shout('mouseUsed');
		}
		_mouseMoveTimeout = setTimeout(function() {
			_mouseMoveTimeout = null;
		}, 100);
	},

	_bindEvents = function() {
		framework.bind(document, 'keydown', self);

		if(_features.transform) {
			// don't bind click event in browsers that don't support transform (mostly IE8)
			framework.bind(self.scrollWrap, 'click', self);
		}
		

		if(!_options.mouseUsed) {
			framework.bind(document, 'mousemove', _onFirstMouseMove);
		}

		framework.bind(window, 'resize scroll', self);

		_shout('bindEvents');
	},

	_unbindEvents = function() {
		framework.unbind(window, 'resize', self);
		framework.unbind(window, 'scroll', _globalEventHandlers.scroll);
		framework.unbind(document, 'keydown', self);
		framework.unbind(document, 'mousemove', _onFirstMouseMove);

		if(_features.transform) {
			framework.unbind(self.scrollWrap, 'click', self);
		}

		if(_isDragging) {
			framework.unbind(window, _upMoveEvents, self);
		}

		_shout('unbindEvents');
	},
	
	_calculatePanBounds = function(zoomLevel, update) {
		var bounds = _calculateItemSize( self.currItem, _viewportSize, zoomLevel );
		if(update) {
			_currPanBounds = bounds;
		}
		return bounds;
	},
	
	_getMinZoomLevel = function(item) {
		if(!item) {
			item = self.currItem;
		}
		return item.initialZoomLevel;
	},
	_getMaxZoomLevel = function(item) {
		if(!item) {
			item = self.currItem;
		}
		return item.w > 0 ? _options.maxSpreadZoom : 1;
	},

	// Return true if offset is out of the bounds
	_modifyDestPanOffset = function(axis, destPanBounds, destPanOffset, destZoomLevel) {
		if(destZoomLevel === self.currItem.initialZoomLevel) {
			destPanOffset[axis] = self.currItem.initialPosition[axis];
			return true;
		} else {
			destPanOffset[axis] = _calculatePanOffset(axis, destZoomLevel); 

			if(destPanOffset[axis] > destPanBounds.min[axis]) {
				destPanOffset[axis] = destPanBounds.min[axis];
				return true;
			} else if(destPanOffset[axis] < destPanBounds.max[axis] ) {
				destPanOffset[axis] = destPanBounds.max[axis];
				return true;
			}
		}
		return false;
	},

	_setupTransforms = function() {

		if(_transformKey) {
			// setup 3d transforms
			var allow3dTransform = _features.perspective && !_likelyTouchDevice;
			_translatePrefix = 'translate' + (allow3dTransform ? '3d(' : '(');
			_translateSufix = _features.perspective ? ', 0px)' : ')';	
			return;
		}

		// Override zoom/pan/move functions in case old browser is used (most likely IE)
		// (so they use left/top/width/height, instead of CSS transform)
	
		_transformKey = 'left';
		framework.addClass(template, 'pswp--ie');

		_setTranslateX = function(x, elStyle) {
			elStyle.left = x + 'px';
		};
		_applyZoomPanToItem = function(item) {

			var zoomRatio = item.fitRatio > 1 ? 1 : item.fitRatio,
				s = item.container.style,
				w = zoomRatio * item.w,
				h = zoomRatio * item.h;

			s.width = w + 'px';
			s.height = h + 'px';
			s.left = item.initialPosition.x + 'px';
			s.top = item.initialPosition.y + 'px';

		};
		_applyCurrentZoomPan = function() {
			if(_currZoomElementStyle) {

				var s = _currZoomElementStyle,
					item = self.currItem,
					zoomRatio = item.fitRatio > 1 ? 1 : item.fitRatio,
					w = zoomRatio * item.w,
					h = zoomRatio * item.h;

				s.width = w + 'px';
				s.height = h + 'px';


				s.left = _panOffset.x + 'px';
				s.top = _panOffset.y + 'px';
			}
			
		};
	},

	_onKeyDown = function(e) {
		var keydownAction = '';
		if(_options.escKey && e.keyCode === 27) { 
			keydownAction = 'close';
		} else if(_options.arrowKeys) {
			if(e.keyCode === 37) {
				keydownAction = 'prev';
			} else if(e.keyCode === 39) { 
				keydownAction = 'next';
			}
		}

		if(keydownAction) {
			// don't do anything if special key pressed to prevent from overriding default browser actions
			// e.g. in Chrome on Mac cmd+arrow-left returns to previous page
			if( !e.ctrlKey && !e.altKey && !e.shiftKey && !e.metaKey ) {
				if(e.preventDefault) {
					e.preventDefault();
				} else {
					e.returnValue = false;
				} 
				self[keydownAction]();
			}
		}
	},

	_onGlobalClick = function(e) {
		if(!e) {
			return;
		}

		// don't allow click event to pass through when triggering after drag or some other gesture
		if(_moved || _zoomStarted || _mainScrollAnimating || _verticalDragInitiated) {
			e.preventDefault();
			e.stopPropagation();
		}
	},

	_updatePageScrollOffset = function() {
		self.setScrollOffset(0, framework.getScrollY());		
	};
	


	



// Micro animation engine
var _animations = {},
	_numAnimations = 0,
	_stopAnimation = function(name) {
		if(_animations[name]) {
			if(_animations[name].raf) {
				_cancelAF( _animations[name].raf );
			}
			_numAnimations--;
			delete _animations[name];
		}
	},
	_registerStartAnimation = function(name) {
		if(_animations[name]) {
			_stopAnimation(name);
		}
		if(!_animations[name]) {
			_numAnimations++;
			_animations[name] = {};
		}
	},
	_stopAllAnimations = function() {
		for (var prop in _animations) {

			if( _animations.hasOwnProperty( prop ) ) {
				_stopAnimation(prop);
			} 
			
		}
	},
	_animateProp = function(name, b, endProp, d, easingFn, onUpdate, onComplete) {
		var startAnimTime = _getCurrentTime(), t;
		_registerStartAnimation(name);

		var animloop = function(){
			if ( _animations[name] ) {
				
				t = _getCurrentTime() - startAnimTime; // time diff
				//b - beginning (start prop)
				//d - anim duration

				if ( t >= d ) {
					_stopAnimation(name);
					onUpdate(endProp);
					if(onComplete) {
						onComplete();
					}
					return;
				}
				onUpdate( (endProp - b) * easingFn(t/d) + b );

				_animations[name].raf = _requestAF(animloop);
			}
		};
		animloop();
	};
	


var publicMethods = {

	// make a few local variables and functions public
	shout: _shout,
	listen: _listen,
	viewportSize: _viewportSize,
	options: _options,

	isMainScrollAnimating: function() {
		return _mainScrollAnimating;
	},
	getZoomLevel: function() {
		return _currZoomLevel;
	},
	getCurrentIndex: function() {
		return _currentItemIndex;
	},
	isDragging: function() {
		return _isDragging;
	},	
	isZooming: function() {
		return _isZooming;
	},
	setScrollOffset: function(x,y) {
		_offset.x = x;
		_currentWindowScrollY = _offset.y = y;
		_shout('updateScrollOffset', _offset);
	},
	applyZoomPan: function(zoomLevel,panX,panY) {
		_panOffset.x = panX;
		_panOffset.y = panY;
		_currZoomLevel = zoomLevel;
		_applyCurrentZoomPan();
	},

	init: function() {

		if(_isOpen || _isDestroying) {
			return;
		}

		var i;

		self.framework = framework; // basic function
		self.template = template; // root DOM element of PhotoSwipe
		self.bg = framework.getChildByClass(template, 'pswp__bg');

		_initalClassName = template.className;
		_isOpen = true;
				
		_features = framework.detectFeatures();
		_requestAF = _features.raf;
		_cancelAF = _features.caf;
		_transformKey = _features.transform;
		_oldIE = _features.oldIE;
		
		self.scrollWrap = framework.getChildByClass(template, 'pswp__scroll-wrap');
		self.container = framework.getChildByClass(self.scrollWrap, 'pswp__container');

		_containerStyle = self.container.style; // for fast access

		// Objects that hold slides (there are only 3 in DOM)
		self.itemHolders = _itemHolders = [
			{el:self.container.children[0] , wrap:0, index: -1},
			{el:self.container.children[1] , wrap:0, index: -1},
			{el:self.container.children[2] , wrap:0, index: -1}
		];

		// hide nearby item holders until initial zoom animation finishes (to avoid extra Paints)
		_itemHolders[0].el.style.display = _itemHolders[2].el.style.display = 'none';

		_setupTransforms();

		// Setup global events
		_globalEventHandlers = {
			resize: self.updateSize,
			scroll: _updatePageScrollOffset,
			keydown: _onKeyDown,
			click: _onGlobalClick
		};

		// disable show/hide effects on old browsers that don't support CSS animations or transforms, 
		// old IOS, Android and Opera mobile. Blackberry seems to work fine, even older models.
		var oldPhone = _features.isOldIOSPhone || _features.isOldAndroid || _features.isMobileOpera;
		if(!_features.animationName || !_features.transform || oldPhone) {
			_options.showAnimationDuration = _options.hideAnimationDuration = 0;
		}

		// init modules
		for(i = 0; i < _modules.length; i++) {
			self['init' + _modules[i]]();
		}
		
		// init
		if(UiClass) {
			var ui = self.ui = new UiClass(self, framework);
			ui.init();
		}

		_shout('firstUpdate');
		_currentItemIndex = _currentItemIndex || _options.index || 0;
		// validate index
		if( isNaN(_currentItemIndex) || _currentItemIndex < 0 || _currentItemIndex >= _getNumItems() ) {
			_currentItemIndex = 0;
		}
		self.currItem = _getItemAt( _currentItemIndex );

		
		if(_features.isOldIOSPhone || _features.isOldAndroid) {
			_isFixedPosition = false;
		}
		
		template.setAttribute('aria-hidden', 'false');
		if(_options.modal) {
			if(!_isFixedPosition) {
				template.style.position = 'absolute';
				template.style.top = framework.getScrollY() + 'px';
			} else {
				template.style.position = 'fixed';
			}
		}

		if(_currentWindowScrollY === undefined) {
			_shout('initialLayout');
			_currentWindowScrollY = _initalWindowScrollY = framework.getScrollY();
		}
		
		// add classes to root element of PhotoSwipe
		var rootClasses = 'pswp--open ';
		if(_options.mainClass) {
			rootClasses += _options.mainClass + ' ';
		}
		if(_options.showHideOpacity) {
			rootClasses += 'pswp--animate_opacity ';
		}
		rootClasses += _likelyTouchDevice ? 'pswp--touch' : 'pswp--notouch';
		rootClasses += _features.animationName ? ' pswp--css_animation' : '';
		rootClasses += _features.svg ? ' pswp--svg' : '';
		framework.addClass(template, rootClasses);

		self.updateSize();

		// initial update
		_containerShiftIndex = -1;
		_indexDiff = null;
		for(i = 0; i < NUM_HOLDERS; i++) {
			_setTranslateX( (i+_containerShiftIndex) * _slideSize.x, _itemHolders[i].el.style);
		}

		if(!_oldIE) {
			framework.bind(self.scrollWrap, _downEvents, self); // no dragging for old IE
		}	

		_listen('initialZoomInEnd', function() {
			self.setContent(_itemHolders[0], _currentItemIndex-1);
			self.setContent(_itemHolders[2], _currentItemIndex+1);

			_itemHolders[0].el.style.display = _itemHolders[2].el.style.display = 'block';

			if(_options.focus) {
				// focus causes layout, 
				// which causes lag during the animation, 
				// that's why we delay it untill the initial zoom transition ends
				template.focus();
			}
			 

			_bindEvents();
		});

		// set content for center slide (first time)
		self.setContent(_itemHolders[1], _currentItemIndex);
		
		self.updateCurrItem();

		_shout('afterInit');

		if(!_isFixedPosition) {

			// On all versions of iOS lower than 8.0, we check size of viewport every second.
			// 
			// This is done to detect when Safari top & bottom bars appear, 
			// as this action doesn't trigger any events (like resize). 
			// 
			// On iOS8 they fixed this.
			// 
			// 10 Nov 2014: iOS 7 usage ~40%. iOS 8 usage 56%.
			
			_updateSizeInterval = setInterval(function() {
				if(!_numAnimations && !_isDragging && !_isZooming && (_currZoomLevel === self.currItem.initialZoomLevel)  ) {
					self.updateSize();
				}
			}, 1000);
		}

		framework.addClass(template, 'pswp--visible');
	},

	// Closes the gallery, then destroy it
	close: function() {
		if(!_isOpen) {
			return;
		}

		_isOpen = false;
		_isDestroying = true;
		_shout('close');
		_unbindEvents();

		_showOrHide( self.currItem, null, true, self.destroy);
	},

	// destroys gallery (unbinds events, cleans up intervals and timeouts to avoid memory leaks)
	destroy: function() {
		_shout('destroy');

		if(_showOrHideTimeout) {
			clearTimeout(_showOrHideTimeout);
		}
		
		//if(_options.modal) {
			template.setAttribute('aria-hidden', 'true');
			template.className = _initalClassName;
		//}

		if(_updateSizeInterval) {
			clearInterval(_updateSizeInterval);
		}

		framework.unbind(self.scrollWrap, _downEvents, self);

		// we unbind lost event at the end, as closing animation may depend on it
		framework.unbind(window, 'scroll', self);

		_stopDragUpdateLoop();

		_stopAllAnimations();

		_listeners = null;
	},

	/**
	 * Pan image to position
	 * @param {Number} x     
	 * @param {Number} y     
	 * @param {Boolean} force Will ignore bounds if set to true.
	 */
	panTo: function(x,y,force) {
		if(!force) {
			if(x > _currPanBounds.min.x) {
				x = _currPanBounds.min.x;
			} else if(x < _currPanBounds.max.x) {
				x = _currPanBounds.max.x;
			}

			if(y > _currPanBounds.min.y) {
				y = _currPanBounds.min.y;
			} else if(y < _currPanBounds.max.y) {
				y = _currPanBounds.max.y;
			}
		}
		
		_panOffset.x = x;
		_panOffset.y = y;
		_applyCurrentZoomPan();
	},
	
	handleEvent: function (e) {
		e = e || window.event;
		if(_globalEventHandlers[e.type]) {
			_globalEventHandlers[e.type](e);
		}
	},


	goTo: function(index) {

		index = _getLoopedId(index);

		var diff = index - _currentItemIndex;
		_indexDiff = diff;

		_currentItemIndex = index;
		self.currItem = _getItemAt( _currentItemIndex );
		_currPositionIndex -= diff;
		
		_moveMainScroll(_slideSize.x * _currPositionIndex);
		

		_stopAllAnimations();
		_mainScrollAnimating = false;

		self.updateCurrItem();
	},
	next: function() {
		self.goTo( _currentItemIndex + 1);
	},
	prev: function() {
		self.goTo( _currentItemIndex - 1);
	},

	// update current zoom/pan objects
	updateCurrZoomItem: function(emulateSetContent) {
		if(emulateSetContent) {
			_shout('beforeChange', 0);
		}

		// itemHolder[1] is middle (current) item
		if(_itemHolders[1].el.children.length) {
			var zoomElement = _itemHolders[1].el.children[0];
			if( framework.hasClass(zoomElement, 'pswp__zoom-wrap') ) {
				_currZoomElementStyle = zoomElement.style;
			} else {
				_currZoomElementStyle = null;
			}
		} else {
			_currZoomElementStyle = null;
		}
		
		_currPanBounds = self.currItem.bounds;	
		_startZoomLevel = _currZoomLevel = self.currItem.initialZoomLevel;

		_panOffset.x = _currPanBounds.center.x;
		_panOffset.y = _currPanBounds.center.y;

		if(emulateSetContent) {
			_shout('afterChange');
		}
	},


	invalidateCurrItems: function() {
		_itemsNeedUpdate = true;
		for(var i = 0; i < NUM_HOLDERS; i++) {
			if( _itemHolders[i].item ) {
				_itemHolders[i].item.needsUpdate = true;
			}
		}
	},

	updateCurrItem: function(beforeAnimation) {

		if(_indexDiff === 0) {
			return;
		}

		var diffAbs = Math.abs(_indexDiff),
			tempHolder;

		if(beforeAnimation && diffAbs < 2) {
			return;
		}


		self.currItem = _getItemAt( _currentItemIndex );
		
		_shout('beforeChange', _indexDiff);

		if(diffAbs >= NUM_HOLDERS) {
			_containerShiftIndex += _indexDiff + (_indexDiff > 0 ? -NUM_HOLDERS : NUM_HOLDERS);
			diffAbs = NUM_HOLDERS;
		}
		for(var i = 0; i < diffAbs; i++) {
			if(_indexDiff > 0) {
				tempHolder = _itemHolders.shift();
				_itemHolders[NUM_HOLDERS-1] = tempHolder; // move first to last

				_containerShiftIndex++;
				_setTranslateX( (_containerShiftIndex+2) * _slideSize.x, tempHolder.el.style);
				self.setContent(tempHolder, _currentItemIndex - diffAbs + i + 1 + 1);
			} else {
				tempHolder = _itemHolders.pop();
				_itemHolders.unshift( tempHolder ); // move last to first

				_containerShiftIndex--;
				_setTranslateX( _containerShiftIndex * _slideSize.x, tempHolder.el.style);
				self.setContent(tempHolder, _currentItemIndex + diffAbs - i - 1 - 1);
			}
			
		}

		// reset zoom/pan on previous item
		if(_currZoomElementStyle && Math.abs(_indexDiff) === 1) {

			var prevItem = _getItemAt(_prevItemIndex);
			if(prevItem.initialZoomLevel !== _currZoomLevel) {
				_calculateItemSize(prevItem , _viewportSize );
				_applyZoomPanToItem( prevItem ); 
			}

		}

		// reset diff after update
		_indexDiff = 0;

		self.updateCurrZoomItem();

		_prevItemIndex = _currentItemIndex;

		_shout('afterChange');
		
	},



	updateSize: function(force) {
		
		if(!_isFixedPosition) {
			var windowScrollY = framework.getScrollY();
			if(_currentWindowScrollY !== windowScrollY) {
				template.style.top = windowScrollY + 'px';
				_currentWindowScrollY = windowScrollY;
			}
			if(!force && _windowVisibleSize.x === window.innerWidth && _windowVisibleSize.y === window.innerHeight) {
				return;
			}
			_windowVisibleSize.x = window.innerWidth;
			_windowVisibleSize.y = window.innerHeight;

			//template.style.width = _windowVisibleSize.x + 'px';
			template.style.height = _windowVisibleSize.y + 'px';
		}



		_viewportSize.x = self.scrollWrap.clientWidth;
		_viewportSize.y = self.scrollWrap.clientHeight;

		_updatePageScrollOffset();

		_slideSize.x = _viewportSize.x + Math.round(_viewportSize.x * _options.spacing);
		_slideSize.y = _viewportSize.y;

		_moveMainScroll(_slideSize.x * _currPositionIndex);

		_shout('beforeResize'); // even may be used for example to switch image sources


		// don't re-calculate size on inital size update
		if(_containerShiftIndex !== undefined) {

			var holder,
				item,
				hIndex;

			for(var i = 0; i < NUM_HOLDERS; i++) {
				holder = _itemHolders[i];
				_setTranslateX( (i+_containerShiftIndex) * _slideSize.x, holder.el.style);

				hIndex = _currentItemIndex+i-1;

				if(_options.loop && _getNumItems() > 2) {
					hIndex = _getLoopedId(hIndex);
				}

				// update zoom level on items and refresh source (if needsUpdate)
				item = _getItemAt( hIndex );

				// re-render gallery item if `needsUpdate`,
				// or doesn't have `bounds` (entirely new slide object)
				if( item && (_itemsNeedUpdate || item.needsUpdate || !item.bounds) ) {

					self.cleanSlide( item );
					
					self.setContent( holder, hIndex );

					// if "center" slide
					if(i === 1) {
						self.currItem = item;
						self.updateCurrZoomItem(true);
					}

					item.needsUpdate = false;

				} else if(holder.index === -1 && hIndex >= 0) {
					// add content first time
					self.setContent( holder, hIndex );
				}
				if(item && item.container) {
					_calculateItemSize(item, _viewportSize);
					_applyZoomPanToItem( item );
				}
				
			}
			_itemsNeedUpdate = false;
		}	

		_startZoomLevel = _currZoomLevel = self.currItem.initialZoomLevel;
		_currPanBounds = self.currItem.bounds;

		if(_currPanBounds) {
			_panOffset.x = _currPanBounds.center.x;
			_panOffset.y = _currPanBounds.center.y;
			_applyCurrentZoomPan();
		}
		
		_shout('resize');
	},
	
	// Zoom current item to
	zoomTo: function(destZoomLevel, centerPoint, speed, easingFn, updateFn) {
		/*
			if(destZoomLevel === 'fit') {
				destZoomLevel = self.currItem.fitRatio;
			} else if(destZoomLevel === 'fill') {
				destZoomLevel = self.currItem.fillRatio;
			}
		*/

		if(centerPoint) {
			_startZoomLevel = _currZoomLevel;
			_midZoomPoint.x = Math.abs(centerPoint.x) - _panOffset.x ;
			_midZoomPoint.y = Math.abs(centerPoint.y) - _panOffset.y ;
			_equalizePoints(_startPanOffset, _panOffset);
		}

		var destPanBounds = _calculatePanBounds(destZoomLevel, false),
			destPanOffset = {};

		_modifyDestPanOffset('x', destPanBounds, destPanOffset, destZoomLevel);
		_modifyDestPanOffset('y', destPanBounds, destPanOffset, destZoomLevel);

		var initialZoomLevel = _currZoomLevel;
		var initialPanOffset = {
			x: _panOffset.x,
			y: _panOffset.y
		};

		_roundPoint(destPanOffset);

		// _startZoomLevel = destZoomLevel;
		var onUpdate = function(now) {
			if(now === 1) {
				_currZoomLevel = destZoomLevel;
				_panOffset.x = destPanOffset.x;
				_panOffset.y = destPanOffset.y;
			} else {
				_currZoomLevel = (destZoomLevel - initialZoomLevel) * now + initialZoomLevel;
				_panOffset.x = (destPanOffset.x - initialPanOffset.x) * now + initialPanOffset.x;
				_panOffset.y = (destPanOffset.y - initialPanOffset.y) * now + initialPanOffset.y;
			}

			if(updateFn) {
				updateFn(now);
			}

			_applyCurrentZoomPan();
		};

		if(speed) {
			_animateProp('customZoomTo', 0, 1, speed, easingFn || framework.easing.sine.inOut, onUpdate);
		} else {
			onUpdate(1);
		}
	}


};