Improve scrolling performance in OOP PDF

chrome/browser/resources/pdf/pdf.js

 // Copyright 2013 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.
 
 'use strict';
 
 <include src="../../../../ui/webui/resources/js/util.js">
 <include src="pdf_scripting_api.js">
 <include src="viewport.js">
 
@@ skipping 34 matching lines @@
   this.pageIndicator_ = $('page-indicator');
   this.progressBar_ = $('progress-bar');
   this.passwordScreen_ = $('password-screen');
   this.passwordScreen_.addEventListener('password-submitted',
                                         this.onPasswordSubmitted_.bind(this));
   this.errorScreen_ = $('error-screen');
 
   // Create the viewport.
   this.viewport_ = new Viewport(window,
                                 this.sizer_,
-                                this.viewportChangedCallback_.bind(this),
+                                this.viewportChanged_.bind(this),
+                                this.beforeZoom_.bind(this),
+                                this.afterZoom_.bind(this),
                                 getScrollbarWidth());
 
   // Create the plugin object dynamically so we can set its src. The plugin
   // element is sized to fill the entire window and is set to be fixed
   // positioning, acting as a viewport. The plugin renders into this viewport
   // according to the scroll position of the window.
   this.plugin_ = document.createElement('object');
   // NOTE: The plugin's 'id' field must be set to 'plugin' since
   // chrome/renderer/printing/print_web_view_helper.cc actually references it.
   this.plugin_.id = 'plugin';
@@ skipping 280 matching lines @@
         this.errorScreen_.text = message.data.loadFailedString;
         break;
       case 'cancelStreamUrl':
         chrome.streamsPrivate.abort(this.streamDetails.streamUrl);
         break;
     }
   },
 
   /**
    * @private
-   * A callback that's called when the viewport changes.
+   * A callback that's called before the zoom changes. Notify the plugin to stop
+   * reacting to scroll events while zoom is taking place to avoid flickering.
    */
-  viewportChangedCallback_: function() {
+  beforeZoom_: function() {
+    this.plugin_.postMessage({
+      type: 'stopScrolling'
+    });
+  },
+
+  /**
+   * @private
+   * A callback that's called after the zoom changes. Notify the plugin of the
+   * zoom change and to continue reacting to scroll events.
+   */
+  afterZoom_: function() {
+    var position = this.viewport_.position;
+    var zoom = this.viewport_.zoom;
+    this.plugin_.postMessage({
+      type: 'viewport',
+      zoom: zoom,
+      xOffset: position.x,
+      yOffset: position.y
+    });
+  },
+
+  /**
+   * @private
+   * A callback that's called after the viewport changes.
+   */
+  viewportChanged_: function() {
     if (!this.documentDimensions_)
       return;
 
     // Update the buttons selected.
     $('fit-to-page-button').classList.remove('polymer-selected');
     $('fit-to-width-button').classList.remove('polymer-selected');
     if (this.viewport_.fittingType == Viewport.FittingType.FIT_TO_PAGE) {
       $('fit-to-page-button').classList.add('polymer-selected');
     } else if (this.viewport_.fittingType ==
                Viewport.FittingType.FIT_TO_WIDTH) {
@@ skipping 15 matching lines @@
     // Update the page indicator.
     var visiblePage = this.viewport_.getMostVisiblePage();
     this.pageIndicator_.index = visiblePage;
     if (this.documentDimensions_.pageDimensions.length > 1 &&
         hasScrollbars.vertical) {
       this.pageIndicator_.style.visibility = 'visible';
     } else {
       this.pageIndicator_.style.visibility = 'hidden';
     }
 
-    var position = this.viewport_.position;
-    var zoom = this.viewport_.zoom;
-    // Notify the plugin of the viewport change.
-    this.plugin_.postMessage({
-      type: 'viewport',
-      zoom: zoom,
-      xOffset: position.x,
-      yOffset: position.y
-    });
-
     var visiblePageDimensions = this.viewport_.getPageScreenRect(visiblePage);
     var size = this.viewport_.size;
     this.sendScriptingMessage_({
       type: 'viewport',
       pageX: visiblePageDimensions.x,
       pageY: visiblePageDimensions.y,
       pageWidth: visiblePageDimensions.width,
       viewportWidth: size.width,
       viewportHeight: size.height,
     });
@@ skipping 64 matching lines @@
 
   /**
    * @type {Viewport} the viewport of the PDF viewer.
    */
   get viewport() {
     return this.viewport_;
   }
 };
 
 var viewer = new PDFViewer();