1// Copyright (c) 2011 The Chromium Authors. All rights reserved.
2// Use of this source code is governed by a BSD-style license that can be
3// found in the LICENSE file.
4
5/**
6 * @fileoverview Card slider implementation. Allows you to create interactions
7 * that have items that can slide left to right to reveal additional items.
8 * Works by adding the necessary event handlers to a specific DOM structure
9 * including a frame, container and cards.
10 * - The frame defines the boundary of one item. Each card will be expanded to
11 *   fill the width of the frame. This element is also overflow hidden so that
12 *   the additional items left / right do not trigger horizontal scrolling.
13 * - The container is what all the touch events are attached to. This element
14 *   will be expanded to be the width of all cards.
15 * - The cards are the individual viewable items. There should be one card for
16 *   each item in the list. Only one card will be visible at a time. Two cards
17 *   will be visible while you are transitioning between cards.
18 *
19 * This class is designed to work well on any hardware-accelerated touch device.
20 * It should still work on pre-hardware accelerated devices it just won't feel
21 * very good. It should also work well with a mouse.
22 */
23
24
25// Use an anonymous function to enable strict mode just for this file (which
26// will be concatenated with other files when embedded in Chrome
27var Slider = (function() {
28  'use strict';
29
30  /**
31   * @constructor
32   * @param {!Element} frame The bounding rectangle that cards are visible in.
33   * @param {!Element} container The surrounding element that will have event
34   *     listeners attached to it.
35   * @param {!Array.<!Element>} cards The individual viewable cards.
36   * @param {number} currentCard The index of the card that is currently
37   *     visible.
38   * @param {number} cardWidth The width of each card should have.
39   */
40  function Slider(frame, container, cards, currentCard, cardWidth) {
41    /**
42     * @type {!Element}
43     * @private
44     */
45    this.frame_ = frame;
46
47    /**
48     * @type {!Element}
49     * @private
50     */
51    this.container_ = container;
52
53    /**
54     * @type {!Array.<!Element>}
55     * @private
56     */
57    this.cards_ = cards;
58
59    /**
60     * @type {number}
61     * @private
62     */
63    this.currentCard_ = currentCard;
64
65    /**
66     * @type {number}
67     * @private
68     */
69    this.cardWidth_ = cardWidth;
70
71    /**
72     * @type {!TouchHandler}
73     * @private
74     */
75    this.touchHandler_ = new TouchHandler(this.container_);
76  }
77
78
79  /**
80   * Events fired by the slider.
81   * Events are fired at the container.
82   */
83  Slider.EventType = {
84    // Fired when the user slides to another card.
85    CARD_CHANGED: 'slider:card_changed'
86  };
87
88
89  /**
90   * The time to transition between cards when animating. Measured in ms.
91   * @type {number}
92   * @private
93   * @const
94   */
95  Slider.TRANSITION_TIME_ = 200;
96
97
98  /**
99   * The minimum velocity required to transition cards if they did not drag past
100   * the halfway point between cards. Measured in pixels / ms.
101   * @type {number}
102   * @private
103   * @const
104   */
105  Slider.TRANSITION_VELOCITY_THRESHOLD_ = 0.2;
106
107
108  Slider.prototype = {
109    /**
110     * The current left offset of the container relative to the frame.
111     * @type {number}
112     * @private
113     */
114    currentLeft_: 0,
115
116    /**
117     * Initialize all elements and event handlers. Must call after construction
118     * and before usage.
119     */
120    initialize: function() {
121      var view = this.container_.ownerDocument.defaultView;
122      assert(view.getComputedStyle(this.container_).display == '-webkit-box',
123          'Container should be display -webkit-box.');
124      assert(view.getComputedStyle(this.frame_).overflow == 'hidden',
125          'Frame should be overflow hidden.');
126      assert(view.getComputedStyle(this.container_).position == 'static',
127          'Container should be position static.');
128      for (var i = 0, card; card = this.cards_[i]; i++) {
129        assert(view.getComputedStyle(card).position == 'static',
130            'Cards should be position static.');
131      }
132
133      this.updateCardWidths_();
134      this.transformToCurrentCard_();
135
136      this.container_.addEventListener(TouchHandler.EventType.TOUCH_START,
137                                       this.onTouchStart_.bind(this));
138      this.container_.addEventListener(TouchHandler.EventType.DRAG_START,
139                                       this.onDragStart_.bind(this));
140      this.container_.addEventListener(TouchHandler.EventType.DRAG_MOVE,
141                                       this.onDragMove_.bind(this));
142      this.container_.addEventListener(TouchHandler.EventType.DRAG_END,
143                                       this.onDragEnd_.bind(this));
144
145      this.touchHandler_.enable(/* opt_capture */ false);
146    },
147
148    /**
149     * Use in cases where the width of the frame has changed in order to update
150     * the width of cards. For example should be used when orientation changes
151     * in full width sliders.
152     * @param {number} newCardWidth Width all cards should have, in pixels.
153     */
154    resize: function(newCardWidth) {
155      if (newCardWidth != this.cardWidth_) {
156        this.cardWidth_ = newCardWidth;
157
158        this.updateCardWidths_();
159
160        // Must upate the transform on the container to show the correct card.
161        this.transformToCurrentCard_();
162      }
163    },
164
165    /**
166     * Sets the cards used. Can be called more than once to switch card sets.
167     * @param {!Array.<!Element>} cards The individual viewable cards.
168     * @param {number} index Index of the card to in the new set of cards to
169     *     navigate to.
170     */
171    setCards: function(cards, index) {
172      assert(index >= 0 && index < cards.length,
173          'Invalid index in Slider#setCards');
174      this.cards_ = cards;
175
176      this.updateCardWidths_();
177
178      // Jump to the given card index.
179      this.selectCard(index);
180    },
181
182    /**
183     * Updates the width of each card.
184     * @private
185     */
186    updateCardWidths_: function() {
187      for (var i = 0, card; card = this.cards_[i]; i++)
188        card.style.width = this.cardWidth_ + 'px';
189    },
190
191    /**
192     * Returns the index of the current card.
193     * @return {number} index of the current card.
194     */
195    get currentCard() {
196      return this.currentCard_;
197    },
198
199    /**
200     * Clear any transition that is in progress and enable dragging for the
201     * touch.
202     * @param {!TouchHandler.Event} e The TouchHandler event.
203     * @private
204     */
205    onTouchStart_: function(e) {
206      this.container_.style.WebkitTransition = '';
207      e.enableDrag = true;
208    },
209
210
211    /**
212     * Tell the TouchHandler that dragging is acceptable when the user begins by
213     * scrolling horizontally.
214     * @param {!TouchHandler.Event} e The TouchHandler event.
215     * @private
216     */
217    onDragStart_: function(e) {
218      e.enableDrag = Math.abs(e.dragDeltaX) > Math.abs(e.dragDeltaY);
219    },
220
221    /**
222     * On each drag move event reposition the container appropriately so the
223     * cards look like they are sliding.
224     * @param {!TouchHandler.Event} e The TouchHandler event.
225     * @private
226     */
227    onDragMove_: function(e) {
228      var deltaX = e.dragDeltaX;
229      // If dragging beyond the first or last card then apply a backoff so the
230      // dragging feels stickier than usual.
231      if (!this.currentCard && deltaX > 0 ||
232          this.currentCard == (this.cards_.length - 1) && deltaX < 0) {
233        deltaX /= 2;
234      }
235      this.translateTo_(this.currentLeft_ + deltaX);
236    },
237
238    /**
239     * Moves the view to the specified position.
240     * @param {number} x Horizontal position to move to.
241     * @private
242     */
243    translateTo_: function(x) {
244      // We use a webkitTransform to slide because this is GPU accelerated on
245      // Chrome and iOS.  Once Chrome does GPU acceleration on the position
246      // fixed-layout elements we could simply set the element's position to
247      // fixed and modify 'left' instead.
248      this.container_.style.WebkitTransform = 'translate3d(' + x + 'px, 0, 0)';
249    },
250
251    /**
252     * On drag end events we may want to transition to another card, depending
253     * on the ending position of the drag and the velocity of the drag.
254     * @param {!TouchHandler.Event} e The TouchHandler event.
255     * @private
256     */
257    onDragEnd_: function(e) {
258      var deltaX = e.dragDeltaX;
259      var velocity = this.touchHandler_.getEndVelocity().x;
260      var newX = this.currentLeft_ + deltaX;
261      var newCardIndex = Math.round(-newX / this.cardWidth_);
262
263      if (newCardIndex == this.currentCard && Math.abs(velocity) >
264          Slider.TRANSITION_VELOCITY_THRESHOLD_) {
265        // If the drag wasn't far enough to change cards but the velocity was
266        // high enough to transition anyways. If the velocity is to the left
267        // (negative) then the user wishes to go right (card +1).
268        newCardIndex += velocity > 0 ? -1 : 1;
269      }
270
271      this.selectCard(newCardIndex, /* animate */ true);
272    },
273
274    /**
275     * Cancel any current touch/slide as if we saw a touch end
276     */
277    cancelTouch: function() {
278      // Stop listening to any current touch
279      this.touchHandler_.cancelTouch();
280
281      // Ensure we're at a card bounary
282      this.transformToCurrentCard_(true);
283    },
284
285    /**
286     * Selects a new card, ensuring that it is a valid index, transforming the
287     * view and possibly calling the change card callback.
288     * @param {number} newCardIndex Index of card to show.
289     * @param {boolean=} opt_animate If true will animate transition from
290     *     current position to new position.
291     */
292    selectCard: function(newCardIndex, opt_animate) {
293      var isChangingCard = newCardIndex >= 0 &&
294          newCardIndex < this.cards_.length &&
295          newCardIndex != this.currentCard;
296      if (isChangingCard) {
297        // If we have a new card index and it is valid then update the left
298        // position and current card index.
299        this.currentCard_ = newCardIndex;
300      }
301
302      this.transformToCurrentCard_(opt_animate);
303
304      if (isChangingCard) {
305        var event = document.createEvent('Event');
306        event.initEvent(Slider.EventType.CARD_CHANGED, true, true);
307        event.slider = this;
308        this.container_.dispatchEvent(event);
309      }
310    },
311
312    /**
313     * Centers the view on the card denoted by this.currentCard. Can either
314     * animate to that card or snap to it.
315     * @param {boolean=} opt_animate If true will animate transition from
316     *     current position to new position.
317     * @private
318     */
319    transformToCurrentCard_: function(opt_animate) {
320      this.currentLeft_ = -this.currentCard * this.cardWidth_;
321
322      // Animate to the current card, which will either transition if the
323      // current card is new, or reset the existing card if we didn't drag
324      // enough to change cards.
325      var transition = '';
326      if (opt_animate) {
327        transition = '-webkit-transform ' + Slider.TRANSITION_TIME_ +
328                     'ms ease-in-out';
329      }
330      this.container_.style.WebkitTransition = transition;
331      this.translateTo_(this.currentLeft_);
332    }
333  };
334
335  return Slider;
336})();
337