[polari] chatView: Don't autoscroll to bottom while reading backlog

[Florian Müllner <fmuellner src gnome org>]

commit d8dd41ec6767edb714219b90a72f34b079c78e7b
Author: Florian Müllner <fmuellner gnome org>
Date:   Fri Oct 11 01:36:11 2013 +0200

    chatView: Don't autoscroll to bottom while reading backlog
    
    Scrolling automatically to the bottom as new messages arrive is
    generally what we want, but it is a horrible disruption when it
    kicks in while the user chose to scroll up to read up on previous
    messages. To fix, only autoscroll while we are scrolled to the
    bottom and keep the current scroll position otherwise.

 src/chatView.js |   13 ++++++++++---
 1 files changed, 10 insertions(+), 3 deletions(-)
---
diff --git a/src/chatView.js b/src/chatView.js
index a2fd3ac..bcb5bed 100644
--- a/src/chatView.js
+++ b/src/chatView.js
@@ -70,6 +70,9 @@ const ChatView = new Lang.Class({
         this._hoveringLink = false;
         this._pending = [];
 
+        let adj = this.widget.vadjustment;
+        this._scrollBottom = adj.upper - adj.page_size;
+
         let app = Gio.Application.get_default();
         app.pasteManager.addWidget(this._view);
 
@@ -264,10 +267,14 @@ const ChatView = new Lang.Class({
     },
 
     _updateScroll: function() {
-        if (this._pending.length == 0)
-            this.widget.vadjustment.value = this.widget.vadjustment.upper;
-        else if (!this._active)
+        let adj = this.widget.vadjustment;
+        if (this._pending.length == 0) {
+            if (adj.value == this._scrollBottom)
+                adj.value = adj.upper - adj.page_size;
+        } else if (!this._active) {
             this._view.scroll_mark_onscreen(this._pending[0].mark);
+        }
+        this._scrollBottom = adj.upper - adj.page_size;
     },
 
     _pendingMessageRemoved: function(channel, message) {