chrome/browser/resources/pdf/viewport_scroller.js

   1 // Copyright 2015 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 'use strict';
   6
   7 /**
   8  * @private
   9  * The period of time in milliseconds to wait between updating the viewport
  10  * position by the scroll velocity.
  11  */
  12 ViewportScroller.DRAG_TIMER_INTERVAL_MS_ = 100;
  13
  14 /**
  15  * @private
  16  * The maximum drag scroll distance per DRAG_TIMER_INTERVAL in pixels.
  17  */
  18 ViewportScroller.MAX_DRAG_SCROLL_DISTANCE_ = 100;
  19
  20 /**
  21  * Creates a new ViewportScroller.
  22  * A ViewportScroller scrolls the page in response to drag selection with the
  23  * mouse.
  24  * @param {Object} viewport The viewport info of the page.
  25  * @param {Object} plugin The PDF plugin element.
  26  * @param {Object} window The window containing the viewer.
  27  */
  28 function ViewportScroller(viewport, plugin, window) {
  29   this.viewport_ = viewport;
  30   this.plugin_ = plugin;
  31   this.window_ = window;
  32   this.mousemoveCallback_ = null;
  33   this.timerId_ = null;
  34   this.scrollVelocity_ = null;
  35   this.lastFrameTime_ = 0;
  36 }
  37
  38 ViewportScroller.prototype = {
  39   /**
  40    * @private
  41    * Start scrolling the page by |scrollVelocity_| every
  42    * |DRAG_TIMER_INTERVAL_MS_|.
  43    */
  44   startDragScrollTimer_: function() {
  45     if (this.timerId_ === null) {
  46       this.timerId_ =
  47           this.window_.setInterval(this.dragScrollPage_.bind(this),
  48                                    ViewportScroller.DRAG_TIMER_INTERVAL_MS_);
  49       this.lastFrameTime_ = Date.now();
  50     }
  51   },
  52
  53   /**
  54    * @private
  55    * Stops the drag scroll timer if it is active.
  56    */
  57   stopDragScrollTimer_: function() {
  58     if (this.timerId_ !== null) {
  59       this.window_.clearInterval(this.timerId_);
  60       this.timerId_ = null;
  61       this.lastFrameTime_ = 0;
  62     }
  63   },
  64
  65   /**
  66    * @private
  67    * Scrolls the viewport by the current scroll velocity.
  68    */
  69   dragScrollPage_: function() {
  70     var position = this.viewport_.position;
  71     var currentFrameTime = Date.now();
  72     var timeAdjustment = (currentFrameTime - this.lastFrameTime_) /
  73                          ViewportScroller.DRAG_TIMER_INTERVAL_MS_;
  74     position.y += (this.scrollVelocity_.y * timeAdjustment);
  75     position.x += (this.scrollVelocity_.x * timeAdjustment);
  76     this.viewport_.position = position;
  77     this.lastFrameTime_ = currentFrameTime;
  78   },
  79
  80   /**
  81    * @private
  82    * Calculate the velocity to scroll while dragging using the distance of the
  83    * cursor outside the viewport.
  84    * @param {Object} event The mousemove event.
  85    * @return {Object} Object with x and y direction scroll velocity.
  86    */
  87   calculateVelocity_: function(event) {
  88     var x = Math.min(Math.max(-event.offsetX,
  89                               event.offsetX - this.plugin_.offsetWidth, 0),
  90                      ViewportScroller.MAX_DRAG_SCROLL_DISTANCE_) *
  91             Math.sign(event.offsetX);
  92     var y = Math.min(Math.max(-event.offsetY,
  93                               event.offsetY - this.plugin_.offsetHeight, 0),
  94                      ViewportScroller.MAX_DRAG_SCROLL_DISTANCE_) *
  95             Math.sign(event.offsetY);
  96     return {
  97       x: x,
  98       y: y
  99     };
 100   },
 101
 102   /**
 103    * @private
 104    * Handles mousemove events. It updates the scroll velocity and starts and
 105    * stops timer based on scroll velocity.
 106    * @param {Object} event The mousemove event.
 107    */
 108   onMousemove_: function(event) {
 109     this.scrollVelocity_ = this.calculateVelocity_(event);
 110     if (!this.scrollVelocity_.x && !this.scrollVelocity_.y)
 111       this.stopDragScrollTimer_();
 112     else if (!this.timerId_)
 113       this.startDragScrollTimer_();
 114   },
 115
 116   /**
 117    * Sets whether to scroll the viewport when the mouse is outside the
 118    * viewport.
 119    * @param {boolean} isSelecting Represents selection status.
 120    */
 121   setEnableScrolling: function(isSelecting) {
 122     if (isSelecting) {
 123       if (!this.mousemoveCallback_)
 124         this.mousemoveCallback_ = this.onMousemove_.bind(this);
 125       this.plugin_.addEventListener('mousemove', this.mousemoveCallback_,
 126                                     false);
 127     } else {
 128       this.stopDragScrollTimer_();
 129       if (this.mousemoveCallback_) {
 130         this.plugin_.removeEventListener('mousemove', this.mousemoveCallback_,
 131                                          false);
 132       }
 133     }
 134   }
 135 };