chrome/browser/resources/pdf/zoom_manager.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  * A class that manages updating the browser with zoom changes.
   9  */
  10 class ZoomManager {
  11   /**
  12    * Constructs a ZoomManager
  13    * @param {!Viewport} viewport A Viewport for which to manage zoom.
  14    * @param {Function} setBrowserZoomFunction A function that sets the browser
  15    *     zoom to the provided value.
  16    * @param {number} defaultZoom The default browser zoom level.
  17    */
  18   constructor(viewport, setBrowserZoomFunction, defaultZoom) {
  19     this.viewport_ = viewport;
  20     this.setBrowserZoomFunction_ = setBrowserZoomFunction;
  21     this.browserZoom_ = defaultZoom;
  22     this.changingBrowserZoom_ = null;
  23   }
  24
  25   /**
  26    * Invoked when a browser-initiated zoom-level change occurs.
  27    * @param {number} newZoom the zoom level to zoom to.
  28    */
  29   onBrowserZoomChange(newZoom) {
  30     // If we are changing the browser zoom level, ignore any browser zoom level
  31     // change events. Either, the change occurred before our update and will be
  32     // overwritten, or the change being reported is the change we are making,
  33     // which we have already handled.
  34     if (this.changingBrowserZoom_)
  35       return;
  36
  37     if (this.floatingPointEquals(this.browserZoom_, newZoom))
  38       return;
  39
  40     this.browserZoom_ = newZoom;
  41     this.viewport_.setZoom(newZoom);
  42   }
  43
  44   /**
  45    * Invoked when an extension-initiated zoom-level change occurs.
  46    */
  47   onPdfZoomChange() {
  48     // If we are already changing the browser zoom level in response to a
  49     // previous extension-initiated zoom-level change, ignore this zoom change.
  50     // Once the browser zoom level is changed, we check whether the extension's
  51     // zoom level matches the most recently sent zoom level.
  52     if (this.changingBrowserZoom_)
  53       return;
  54
  55     let zoom = this.viewport_.zoom;
  56     if (this.floatingPointEquals(this.browserZoom_, zoom))
  57       return;
  58
  59     this.changingBrowserZoom_ = this.setBrowserZoomFunction_(zoom).then(
  60         function() {
  61       this.browserZoom_ = zoom;
  62       this.changingBrowserZoom_ = null;
  63
  64       // The extension's zoom level may have changed while the browser zoom
  65       // change was in progress. We call back into onPdfZoomChange to ensure the
  66       // browser zoom is up to date.
  67       this.onPdfZoomChange();
  68     }.bind(this));
  69   }
  70
  71   /**
  72    * Returns whether two numbers are approximately equal.
  73    * @param {number} a The first number.
  74    * @param {number} b The second number.
  75    */
  76   floatingPointEquals(a, b) {
  77     let MIN_ZOOM_DELTA = 0.01;
  78     // If the zoom level is close enough to the current zoom level, don't
  79     // change it. This avoids us getting into an infinite loop of zoom changes
  80     // due to floating point error.
  81     return Math.abs(a - b) <= MIN_ZOOM_DELTA;
  82   }
  83 };