From d85e38d629cf740a3bd2ad978f1a832f47d2bfeb Mon Sep 17 00:00:00 2001
From: Brendan Dahl <brendan.dahl@gmail.com>
Date: Mon, 5 Aug 2013 16:34:57 -0700
Subject: [PATCH] Fix intermittent blank page on fast zoom.

---
 src/api.js    |  2 +-
 web/viewer.js | 15 ++++++++++++---
 2 files changed, 13 insertions(+), 4 deletions(-)

diff --git a/src/api.js b/src/api.js
index 902075d43..9285606a9 100644
--- a/src/api.js
+++ b/src/api.js
@@ -852,7 +852,7 @@ var InternalRenderTask = (function InternalRenderTaskClosure() {
     cancel: function InternalRenderTask_cancel() {
       this.running = false;
       this.cancelled = true;
-      this.callback();
+      this.callback('cancelled');
     },
 
     operatorListChanged: function InternalRenderTask_operatorListChanged() {
diff --git a/web/viewer.js b/web/viewer.js
index d1b01ff00..3e2ca141d 100644
--- a/web/viewer.js
+++ b/web/viewer.js
@@ -1560,7 +1560,6 @@ var PageView = function pageView(container, id, scale,
   this.update = function pageViewUpdate(scale, rotation) {
     if (this.renderTask) {
       this.renderTask.cancel();
-      this.renderTask = null;
     }
     this.resume = null;
     this.renderingState = RenderingStates.INITIAL;
@@ -1828,8 +1827,18 @@ var PageView = function pageView(container, id, scale,
 
     var self = this;
     function pageViewDrawCallback(error) {
+      // The renderTask may have been replaced by a new one, so only remove the
+      // reference to the renderTask if it matches the one that is triggering
+      // this callback.
+      if (renderTask === self.renderTask) {
+        self.renderTask = null;
+      }
+
+      if (error === 'cancelled') {
+        return;
+      }
+
       self.renderingState = RenderingStates.FINISHED;
-      self.renderTask = null;
 
       if (self.loadingIconDiv) {
         div.removeChild(self.loadingIconDiv);
@@ -1890,7 +1899,7 @@ var PageView = function pageView(container, id, scale,
         cont();
       }
     };
-    this.renderTask = this.pdfPage.render(renderContext);
+    var renderTask = this.renderTask = this.pdfPage.render(renderContext);
 
     this.renderTask.then(
       function pdfPageRenderCallback() {