Reduce the number of calls to PDFView.getVisiblePages from updateViewarea

web/viewer.js

@@ -1205,14 +1205,15 @@ var PDFView = {
     }
   },
 
-  renderHighestPriority: function pdfViewRenderHighestPriority() {
+  renderHighestPriority:
+      function pdfViewRenderHighestPriority(currentlyVisiblePages) {
     if (PDFView.idleTimeout) {
       clearTimeout(PDFView.idleTimeout);
       PDFView.idleTimeout = null;
     }
 
     // Pages have a higher priority than thumbnails, so check them first.
-    var visiblePages = this.getVisiblePages();
+    var visiblePages = currentlyVisiblePages || this.getVisiblePages();
     var pageView = this.getHighestPriority(visiblePages, this.pages,
                                            this.pageViewScroll.down);
     if (pageView) {
@@ -1925,7 +1926,7 @@ function updateViewarea() {
     return;
   }
 
-  PDFView.renderHighestPriority();
+  PDFView.renderHighestPriority(visible);
 
   var currentId = PDFView.page;
   var firstPage = visible.first;