Use a specialized new tab page in TOUCH_UI builds

chrome/browser/resources/touch_ntp/slider.js

+// Copyright (c) 2011 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+/**
+ * @fileoverview Card slider implementation. Allows you to create interactions
+ * that have items that can slide left to right to reveal additional items.
+ * Works by adding the necessary event handlers to a specific DOM structure
+ * including a frame, container and cards.
+ * - The frame defines the boundary of one item. Each card will be expanded to
+ *   fill the width of the frame. This element is also overflow hidden so that
+ *   the additional items left / right do not trigger horizontal scrolling.
+ * - The container is what all the touch events are attached to. This element
+ *   will be expanded to be the width of all cards.
+ * - The cards are the individual viewable items. There should be one card for
+ *   each item in the list. Only one card will be visible at a time. Two cards
+ *   will be visible while you are transitioning between cards.
+ *
+ * This class is designed to work well on any hardware-accelerated touch device.
+ * It should still work on pre-hardware accelerated devices it just won't feel
+ * very good. It should also work well with a mouse.
+ */
+'use strict';
+
+/**
+ * @constructor
+ * @param {!Element} frame The bounding rectangle that cards are visible in.
+ * @param {!Element} container The surrounding element that will have event
+ *     listeners attached to it.
+ * @param {!Array.<!Element>} cards The individual viewable cards.
+ * @param {number} currentCard The index of the card that is currently visible.
+ * @param {number} cardWidth The width of each card should have.
+ */
+function Slider(frame, container, cards, currentCard, cardWidth) {
+  /**
+   * @type {!Element}
+   * @private
+   */
+  this.frame_ = frame;
+
+  /**
+   * @type {!Element}
+   * @private
+   */
+  this.container_ = container;
+
+  /**
+   * @type {!Array.<!Element>}
+   * @private
+   */
+  this.cards_ = cards;
+
+  /**
+   * @type {number}
+   * @private
+   */
+  this.currentCard_ = currentCard;
+
+  /**
+   * @type {number}
+   * @private
+   */
+  this.cardWidth_ = cardWidth;
+
+  /**
+   * @type {!TouchHandler}
+   * @private
+   */
+  this.touchHandler_ = new TouchHandler(this.container_);
+}
+
+
+/**
+ * Events fired by the slider.
+ * Events are fired at the container.
+ */
+Slider.EventType = {
+  // Fired when the user slides to another card.
+  CARD_CHANGED: 'slider:card_changed'
+};
+
+
+/**
+ * The time to transition between cards when animating. Measured in ms.
+ * @type {number}
+ * @private
+ * @const
+ */
+Slider.TRANSITION_TIME_ = 200;
+
+
+/**
+ * The minimum velocity required to transition cards if they did not drag past
+ * the halfway point between cards. Measured in pixels / ms.
+ * @type {number}
+ * @private
+ * @const
+ */
+Slider.TRANSITION_VELOCITY_THRESHOLD_ = 0.2;
+
+
+Slider.prototype = {
+  /**
+   * The current left offset of the container relative to the frame.
+   * @type {number}
+   * @private
+   */
+  currentLeft_: 0,
+
+  /**
+   * Initialize all elements and event handlers. Must call after construction
+   * and before usage.
+   */
+  initialize: function() {
+    var view = this.container_.ownerDocument.defaultView;
+    assert(view.getComputedStyle(this.container_).display == '-webkit-box',
+        'Container should be display -webkit-box.');
+    assert(view.getComputedStyle(this.frame_).overflow == 'hidden',
+        'Frame should be overflow hidden.');
+    assert(view.getComputedStyle(this.container_).position == 'static',
+        'Container should be position static.');
+    for (var i = 0, card; card = this.cards_[i]; i++) {
+      assert(view.getComputedStyle(card).position == 'static',
+          'Cards should be position static.');
+    }
+
+    this.updateCardWidths_();
+    this.transformToCurrentCard_();
+
+    this.container_.addEventListener(TouchHandler.EventType.TOUCH_START,
+                                     this.onTouchStart_.bind(this));
+    this.container_.addEventListener(TouchHandler.EventType.DRAG_START,
+                                     this.onDragStart_.bind(this));
+    this.container_.addEventListener(TouchHandler.EventType.DRAG_MOVE,
+                                     this.onDragMove_.bind(this));
+    this.container_.addEventListener(TouchHandler.EventType.DRAG_END,
+                                     this.onDragEnd_.bind(this));
+
+    this.touchHandler_.enable(/* opt_capture */ false);
+  },
+
+  /**
+   * Use in cases where the width of the frame has changed in order to update
+   * the width of cards. For example should be used when orientation changes in
+   * full width sliders.
+   * @param {number} newCardWidth Width all cards should have, in pixels.
+   */
+  resize: function(newCardWidth) {
+    if (newCardWidth != this.cardWidth_) {
+      this.cardWidth_ = newCardWidth;
+
+      this.updateCardWidths_();
+
+      // Must upate the transform on the container to show the correct card.
+      this.transformToCurrentCard_();
+    }
+  },
+
+  /**
+   * Sets the cards used. Can be called more than once to switch card sets.
+   * @param {!Array.<!Element>} cards The individual viewable cards.
+   * @param {number} index Index of the card to in the new set of cards to
+   *     navigate to.
+   */
+  setCards: function(cards, index) {
+    assert(index >= 0 && index < cards.length,
+        'Invalid index in Slider#setCards');
+    this.cards_ = cards;
+
+    this.updateCardWidths_();
+
+    // Jump to the given card index.
+    this.selectCard(index);
+  },
+
+  /**
+   * Updates the width of each card.
+   * @private
+   */
+  updateCardWidths_: function() {
+    for (var i = 0, card; card = this.cards_[i]; i++)
+      card.style.width = this.cardWidth_ + 'px';
+  },
+
+  /**
+   * Returns the index of the current card.
+   * @return {number} index of the current card.
+   */
+  get currentCard() {
+    return this.currentCard_;
+  },
+
+  /**
+   * Clear any transition that is in progress and enable dragging for the touch.
+   * @param {!TouchHandler.Event} e The TouchHandler event.
+   * @private
+   */
+  onTouchStart_: function(e) {
+    this.container_.style.WebkitTransition = '';
+    e.enableDrag = true;
+  },
+
+
+  /**
+   * Tell the TouchHandler that dragging is acceptable when the user begins by
+   * scrolling horizontally.
+   * @param {!TouchHandler.Event} e The TouchHandler event.
+   * @private
+   */
+  onDragStart_: function(e) {
+    e.enableDrag = Math.abs(e.dragDeltaX) > Math.abs(e.dragDeltaY);
+  },
+
+  /**
+   * On each drag move event reposition the container appropriately so the cards
+   * look like they are sliding.
+   * @param {!TouchHandler.Event} e The TouchHandler event.
+   * @private
+   */
+  onDragMove_: function(e) {
+    var deltaX = e.dragDeltaX;
+    // If dragging beyond the first or last card then apply a backoff so the
+    // dragging feels stickier than usual.
+    if (!this.currentCard && deltaX > 0 ||
+        this.currentCard == (this.cards_.length - 1) && deltaX < 0) {
+      deltaX /= 2;
+    }
+    this.translateTo_(this.currentLeft_ + deltaX);
+  },
+
+  /**
+   * Moves the view to the specified position.
+   * @param {number} x Horizontal position to move to.
+   * @private
+   */
+  translateTo_: function(x) {
+    // We use a webkitTransform to slide because this is GPU accelerated on
+    // Chrome and iOS.  Once Chrome does GPU acceleration on the position
+    // fixed-layout elements we could simply set the element's position to
+    // fixed and modify 'left' instead.
+    this.container_.style.WebkitTransform = 'translate3d(' + x + 'px, 0, 0)';
+  },
+
+  /**
+   * On drag end events we may want to transition to another card, depending on
+   * the ending position of the drag and the velocity of the drag.
+   * @param {!TouchHandler.Event} e The TouchHandler event.
+   * @private
+   */
+  onDragEnd_: function(e) {
+    var deltaX = e.dragDeltaX;
+    var velocity = this.touchHandler_.getEndVelocity().x;
+    var newX = this.currentLeft_ + deltaX;
+    var newCardIndex = Math.round(-newX / this.cardWidth_);
+
+    if (newCardIndex == this.currentCard && Math.abs(velocity) >
+        Slider.TRANSITION_VELOCITY_THRESHOLD_) {
+      // If the drag wasn't far enough to change cards but the velocity was high
+      // enough to transition anyways.
+      // If the velocity is to the left (negative) then the user wishes to go
+      // right (card +1).
+      newCardIndex += velocity > 0 ? -1 : 1;
+    }
+
+    this.selectCard(newCardIndex, /* animate */ true);
+  },
+
+  /**
+   * Cancel any current touch/slide as if we saw a touch end
+   */
+  cancelTouch: function() {
+    // Stop listening to any current touch
+    this.touchHandler_.cancelTouch();
+
+    // Ensure we're at a card bounary
+    this.transformToCurrentCard_(true);
+  },
+
+  /**
+   * Selects a new card, ensuring that it is a valid index, transforming the
+   * view and possibly calling the change card callback.
+   * @param {number} newCardIndex Index of card to show.
+   * @param {boolean=} opt_animate If true will animate transition from current
+   *     position to new position.
+   */
+  selectCard: function(newCardIndex, opt_animate) {
+    var isChangingCard = newCardIndex >= 0 &&
+        newCardIndex < this.cards_.length &&
+        newCardIndex != this.currentCard;
+    if (isChangingCard) {
+      // If we have a new card index and it is valid then update the left
+      // position and current card index.
+      this.currentCard_ = newCardIndex;
+    }
+
+    this.transformToCurrentCard_(opt_animate);
+
+    if (isChangingCard) {
+      var event = document.createEvent('Event');
+      event.initEvent(Slider.EventType.CARD_CHANGED, true, true);
+      event.slider = this;
+      this.container_.dispatchEvent(event);
+    }
+  },
+
+  /**
+   * Centers the view on the card denoted by this.currentCard. Can either
+   * animate to that card or snap to it.
+   * @param {boolean=} opt_animate If true will animate transition from current
+   *     position to new position.
+   * @private
+   */
+  transformToCurrentCard_: function(opt_animate) {
+    this.currentLeft_ = -this.currentCard * this.cardWidth_;
+
+    // Animate to the current card, which will either transition if the current
+    // card is new, or reset the existing card if we didn't drag enough to
+    // change cards.
+    var transition = '';
+    if (opt_animate) {
+        transition = '-webkit-transform ' + Slider.TRANSITION_TIME_ +
+                     'ms ease-in-out';
+    }
+    this.container_.style.WebkitTransition = transition;
+    this.translateTo_(this.currentLeft_);
+  }
+};