From 92529e2b1173841832e9b1cbd429f14c45683cc2 Mon Sep 17 00:00:00 2001
From: Jonas Jenwald <jonas.jenwald@gmail.com>
Date: Tue, 30 May 2017 15:50:37 +0200
Subject: [PATCH] Refactor the `getTempCanvas` function in
 `pdf_thumbnail_view.js` to a factory, in preparation for ES6 conversion of
 the thumbnail related code

This patch intends to simplify future ES6 refactoring of the thumbnail code, since the current code isn't going to work well together with proper `Class`es.
---
 web/pdf_thumbnail_view.js   | 74 +++++++++++++++++++++++--------------
 web/pdf_thumbnail_viewer.js |  9 +----
 2 files changed, 48 insertions(+), 35 deletions(-)

diff --git a/web/pdf_thumbnail_view.js b/web/pdf_thumbnail_view.js
index 6d4aca892..de9e885d1 100644
--- a/web/pdf_thumbnail_view.js
+++ b/web/pdf_thumbnail_view.js
@@ -32,35 +32,52 @@ var THUMBNAIL_CANVAS_BORDER_WIDTH = 1; // px
  *   but increases the overall memory usage. The default value is false.
  */
 
+const TempImageFactory = (function TempImageFactoryClosure() {
+  let tempCanvasCache = null;
+
+  return {
+    getCanvas(width, height) {
+      let tempCanvas = tempCanvasCache;
+      if (!tempCanvas) {
+        tempCanvas = document.createElement('canvas');
+        tempCanvasCache = tempCanvas;
+      }
+      tempCanvas.width = width;
+      tempCanvas.height = height;
+
+      // Since this is a temporary canvas, we need to fill it with a white
+      // background ourselves. `_getPageDrawContext` uses CSS rules for this.
+      if (typeof PDFJSDev === 'undefined' ||
+          PDFJSDev.test('MOZCENTRAL || FIREFOX || GENERIC')) {
+        tempCanvas.mozOpaque = true;
+      }
+
+      let ctx = tempCanvas.getContext('2d', { alpha: false, });
+      ctx.save();
+      ctx.fillStyle = 'rgb(255, 255, 255)';
+      ctx.fillRect(0, 0, width, height);
+      ctx.restore();
+      return tempCanvas;
+    },
+
+    destroyCanvas() {
+      let tempCanvas = tempCanvasCache;
+      if (tempCanvas) {
+        // Zeroing the width and height causes Firefox to release graphics
+        // resources immediately, which can greatly reduce memory consumption.
+        tempCanvas.width = 0;
+        tempCanvas.height = 0;
+      }
+      tempCanvasCache = null;
+    },
+  };
+})();
+
 /**
  * @class
  * @implements {IRenderableView}
  */
 var PDFThumbnailView = (function PDFThumbnailViewClosure() {
-  function getTempCanvas(width, height) {
-    var tempCanvas = PDFThumbnailView.tempImageCache;
-    if (!tempCanvas) {
-      tempCanvas = document.createElement('canvas');
-      PDFThumbnailView.tempImageCache = tempCanvas;
-    }
-    tempCanvas.width = width;
-    tempCanvas.height = height;
-
-    // Since this is a temporary canvas, we need to fill the canvas with a white
-    // background ourselves. `_getPageDrawContext` uses CSS rules for this.
-    if (typeof PDFJSDev === 'undefined' ||
-        PDFJSDev.test('MOZCENTRAL || FIREFOX || GENERIC')) {
-      tempCanvas.mozOpaque = true;
-    }
-
-    var ctx = tempCanvas.getContext('2d', {alpha: false});
-    ctx.save();
-    ctx.fillStyle = 'rgb(255, 255, 255)';
-    ctx.fillRect(0, 0, width, height);
-    ctx.restore();
-    return tempCanvas;
-  }
-
   /**
    * @constructs PDFThumbnailView
    * @param {PDFThumbnailViewOptions} options
@@ -358,7 +375,8 @@ var PDFThumbnailView = (function PDFThumbnailViewClosure() {
       var MAX_NUM_SCALING_STEPS = 3;
       var reducedWidth = canvas.width << MAX_NUM_SCALING_STEPS;
       var reducedHeight = canvas.height << MAX_NUM_SCALING_STEPS;
-      var reducedImage = getTempCanvas(reducedWidth, reducedHeight);
+      var reducedImage = TempImageFactory.getCanvas(reducedWidth,
+                                                    reducedHeight);
       var reducedImageCtx = reducedImage.getContext('2d');
 
       while (reducedWidth > img.width || reducedHeight > img.height) {
@@ -405,11 +423,13 @@ var PDFThumbnailView = (function PDFThumbnailViewClosure() {
     },
   };
 
+  PDFThumbnailView.cleanup = function() {
+    TempImageFactory.destroyCanvas();
+  };
+
   return PDFThumbnailView;
 })();
 
-PDFThumbnailView.tempImageCache = null;
-
 export {
   PDFThumbnailView,
 };
diff --git a/web/pdf_thumbnail_viewer.js b/web/pdf_thumbnail_viewer.js
index d1c1d81a4..fbc7f80e4 100644
--- a/web/pdf_thumbnail_viewer.js
+++ b/web/pdf_thumbnail_viewer.js
@@ -104,14 +104,7 @@ var PDFThumbnailViewer = (function PDFThumbnailViewerClosure() {
     },
 
     cleanup: function PDFThumbnailViewer_cleanup() {
-      var tempCanvas = PDFThumbnailView.tempImageCache;
-      if (tempCanvas) {
-        // Zeroing the width and height causes Firefox to release graphics
-        // resources immediately, which can greatly reduce memory consumption.
-        tempCanvas.width = 0;
-        tempCanvas.height = 0;
-      }
-      PDFThumbnailView.tempImageCache = null;
+      PDFThumbnailView.cleanup();
     },
 
     /**