[gnome-shell] telepathyClient: Fix auto-scroll to bottom

[Guillaume Desmottes <gdesmott src gnome org>]

commit c77b38fc4fd42d0851a0c40e2402b51aa4d08e82
Author: Sjoerd Simons <sjoerd luon net>
Date:   Sun Oct 21 14:11:45 2012 +0200

    telepathyClient: Fix auto-scroll to bottom
    
    Instead of keeping track of the old adjustment.upper keep track of the
    old adjustment.value that corresponded to the bottom scroll position.
    
    This fixes the integrated chatview not always scrolling to the bottom
    by removing the assumption that page_size is constant between updates,
    which is not the case as the view is presented in various different ways.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=686571

 js/ui/components/telepathyClient.js |   10 ++++++----
 1 files changed, 6 insertions(+), 4 deletions(-)
---
diff --git a/js/ui/components/telepathyClient.js b/js/ui/components/telepathyClient.js
index a487352..dc7da4d 100644
--- a/js/ui/components/telepathyClient.js
+++ b/js/ui/components/telepathyClient.js
@@ -771,16 +771,18 @@ const ChatNotification = new Lang.Class({
             this.emit('unfocused');
         }));
 
-        this._oldMaxScrollAdjustment = 0;
         this._createScrollArea();
         this._lastGroup = null;
         this._lastGroupActor = null;
 
+        // Keep track of the bottom position for the current adjustment and
+        // force a scroll to the bottom if things change while we were at the
+        // bottom
+        this._oldMaxScrollValue = this._scrollArea.vscroll.adjustment.value;
         this._scrollArea.vscroll.adjustment.connect('changed', Lang.bind(this, function(adjustment) {
-            let currentValue = adjustment.value + adjustment.page_size;
-            if (currentValue == this._oldMaxScrollAdjustment)
+            if (adjustment.value == this._oldMaxScrollValue)
                 this.scrollTo(St.Side.BOTTOM);
-            this._oldMaxScrollAdjustment = adjustment.upper;
+            this._oldMaxScrollValue = Math.max(adjustment.lower, adjustment.upper - adjustment.page_size);
         }));
 
         this._inputHistory = new History.HistoryManager({ entry: this._responseEntry.clutter_text });