From edf3163fa6ca3f2bf73b2fd10bdf40b7d24c2d29 Mon Sep 17 00:00:00 2001
From: Jonas <Snuffleupagus@server.fake>
Date: Wed, 31 Jul 2013 19:43:03 +0200
Subject: [PATCH] Keep current scroll position when zooming the document

---
 web/viewer.js | 86 +++++++++++++++++++++++++++++++++------------------
 1 file changed, 56 insertions(+), 30 deletions(-)

diff --git a/web/viewer.js b/web/viewer.js
index fd10930eb..141a092c6 100644
--- a/web/viewer.js
+++ b/web/viewer.js
@@ -251,28 +251,45 @@ var PDFView = {
     }, true);
   },
 
-  setScale: function pdfViewSetScale(val, resetAutoSettings, noScroll) {
-    if (val == this.currentScale)
+  getPageTop: function pdfViewGetPageTop(id) {
+    return (this.pages[id - 1].el.offsetTop + this.pages[id - 1].el.clientTop);
+  },
+
+  setScale: function pdfViewSetScale(value, resetAutoSettings, noScroll) {
+    if (this.currentScale === value) {
       return;
+    }
 
-    var pages = this.pages;
-    for (var i = 0; i < pages.length; i++)
-      pages[i].update(val * CSS_UNITS);
+    var pages = this.pages, page = this.page;
+    var currentPage = pages[page - 1], dest = null;
+    if (!noScroll && !this.isPresentationMode) {
+      // Obtain the current scroll position before resizing the pages.
+      var topLeft = currentPage.getPagePoint(this.container.scrollLeft,
+        (this.container.scrollTop - this.getPageTop(page)));
+      dest = [null, { name: 'XYZ' }, Math.round(topLeft[0]),
+              Math.round(topLeft[1]), null];
+    }
 
-    if (!noScroll && this.currentScale != val)
-      this.pages[this.page - 1].scrollIntoView();
-    this.currentScale = val;
+    for (var i = 0; i < pages.length; i++) {
+      pages[i].update(value * CSS_UNITS);
+    }
+    this.currentScale = value;
+
+    if (!noScroll) {
+      currentPage.scrollIntoView(dest);
+    }
 
     var event = document.createEvent('UIEvents');
     event.initUIEvent('scalechange', false, false, window, 0);
-    event.scale = val;
+    event.scale = value;
     event.resetAutoSettings = resetAutoSettings;
     window.dispatchEvent(event);
   },
 
   parseScale: function pdfViewParseScale(value, resetAutoSettings, noScroll) {
-    if ('custom' == value)
+    if ('custom' === value) {
       return;
+    }
 
     var scale = parseFloat(value);
     this.currentScaleValue = value;
@@ -1040,14 +1057,14 @@ var PDFView = {
     } else if (storedHash) {
       this.setHash(storedHash);
     } else if (scale) {
-      this.parseScale(scale, true);
+      this.parseScale(scale, true, true);
       this.page = 1;
     }
 
     if (PDFView.currentScale === UNKNOWN_SCALE) {
       // Scale was not initialized: invalid bookmark or scale was not specified.
       // Setting the default one.
-      this.parseScale(DEFAULT_SCALE, true);
+      this.parseScale(DEFAULT_SCALE, true, true);
     }
   },
 
@@ -1372,15 +1389,28 @@ var PDFView = {
 
   enterPresentationMode: function pdfViewEnterPresentationMode() {
     this.isPresentationMode = true;
-    this.page = this.presentationModeArgs.page;
     this.parseScale('page-fit', true);
+    // Since 'resize' events are fired when entering presentation mode,
+    // add this call to the end of the rendering queue to prevent
+    // the page from being scrolled partially out of view.
+    setTimeout(function() {
+      this.page = this.presentationModeArgs.page;
+    }.bind(this), 0);
+
     this.showPresentationControls();
   },
 
   exitPresentationMode: function pdfViewExitPresentationMode() {
     this.isPresentationMode = false;
-    this.parseScale(this.presentationModeArgs.previousScale);
-    this.page = this.page;
+    var currentPage = this.pages[this.page - 1];
+    this.parseScale(this.presentationModeArgs.previousScale, true, true);
+    // Since 'resize' events are fired when exiting from presentation mode,
+    // add this call to the end of the rendering queue to make sure
+    // that the current page is scrolled into view properly.
+    setTimeout(function() {
+      currentPage.scrollIntoView();
+    }, 0);
+
     this.clearMouseScrollState();
     this.hidePresentationControls();
     this.presentationModeArgs = null;
@@ -1434,14 +1464,9 @@ var PDFView = {
     this.renderHighestPriority();
 
     var currentPage = this.pages[this.page - 1];
-    if (!currentPage) {
-      return;
-    }
-
-    // Wait for presentation mode to take effect
-    setTimeout(function() {
+    if (currentPage) {
       currentPage.scrollIntoView();
-    }, 0);
+    }
   },
 
   /**
@@ -2490,9 +2515,10 @@ function updateViewarea() {
 window.addEventListener('resize', function webViewerResize(evt) {
   if (PDFView.initialized &&
       (document.getElementById('pageWidthOption').selected ||
-      document.getElementById('pageFitOption').selected ||
-      document.getElementById('pageAutoOption').selected))
-      PDFView.parseScale(document.getElementById('scaleSelect').value);
+       document.getElementById('pageFitOption').selected ||
+       document.getElementById('pageAutoOption').selected)) {
+    PDFView.parseScale(document.getElementById('scaleSelect').value);
+  }
   updateViewarea();
 });
 
@@ -2567,11 +2593,11 @@ window.addEventListener('scalechange', function scalechange(evt) {
   customScaleOption.selected = false;
 
   if (!evt.resetAutoSettings &&
-       (document.getElementById('pageWidthOption').selected ||
-        document.getElementById('pageFitOption').selected ||
-        document.getElementById('pageAutoOption').selected)) {
-      updateViewarea();
-      return;
+      (document.getElementById('pageWidthOption').selected ||
+       document.getElementById('pageFitOption').selected ||
+       document.getElementById('pageAutoOption').selected)) {
+    updateViewarea();
+    return;
   }
 
   var predefinedValueFound = selectScaleOption('' + evt.scale);