From 121c165a39bb533a1670b0be3e7a2311ca418f73 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Lorenz=20H=C3=BCbschle-Schneider?=
 <lorenz-dev@lgh-alumni.de>
Date: Sat, 13 Sep 2014 17:58:31 +0100
Subject: [PATCH] Scroll to correct position when fetching more lines

Fixes #406
---
 js/connection.js  | 27 ++++++++++++---------------
 js/glowingbear.js | 10 +++++++---
 2 files changed, 19 insertions(+), 18 deletions(-)

diff --git a/js/connection.js b/js/connection.js
index 2945d4a..f938783 100644
--- a/js/connection.js
+++ b/js/connection.js
@@ -234,9 +234,10 @@ weechat.factory('connection',
 //XXX move to handlers?
             // delete old lines and add new ones
             var oldLength = buffer.lines.length;
-            // Whether to set the readmarker to the middle position
-            // Don't do that if we didn't get any more lines than we already had
-            var setReadmarker = (buffer.lastSeen >= 0) && (oldLength !== buffer.lines.length);
+            // whether we already had all unread lines
+            var hadAllUnreadLines = buffer.lastSeen >= 0;
+
+            // clear the old lines
             buffer.lines.length = 0;
             // We need to set the number of requested lines to 0 here, because parsing a line
             // increments it. This is needed to also count newly arriving lines while we're
@@ -248,23 +249,19 @@ weechat.factory('connection',
             // Parse the lines
             handlers.handleLineInfo(lineinfo, true);
 
-            if (setReadmarker) {
-                // Read marker was somewhere in the old lines - we don't need it any more,
-                // set it to the boundary between old and new. This way, we stay at the exact
-                // same position in the text through the scrollWithBuffer below
-                buffer.lastSeen = buffer.lines.length - oldLength - 1;
-            } else {
-                // We are currently fetching at least some unread lines, so we need to keep
-                // the read marker position correct
-                buffer.lastSeen -= oldLength;
-            }
+            // Correct the read marker for the lines that were counted twice
+            buffer.lastSeen -= oldLength;
+
             // We requested more lines than we got, no more lines.
             if (linesReceivedCount < numLines) {
                 buffer.allLinesFetched = true;
             }
             $rootScope.loadingLines = false;
-            // Scroll read marker to the center of the screen
-            $rootScope.scrollWithBuffer(true);
+
+            // Only scroll to read marker if we didn't have all unread lines previously, but have them now
+            var scrollToReadmarker = !hadAllUnreadLines && buffer.lastSeen >= 0;
+            // Scroll to correct position
+            $rootScope.scrollWithBuffer(scrollToReadmarker, true);
         });
     };
 
diff --git a/js/glowingbear.js b/js/glowingbear.js
index d307890..0b2a5b6 100644
--- a/js/glowingbear.js
+++ b/js/glowingbear.js
@@ -432,7 +432,7 @@ weechat.controller('WeechatCtrl', ['$rootScope', '$scope', '$store', '$timeout',
         return connection.fetchMoreLines(numLines);
     };
 
-    $rootScope.scrollWithBuffer = function(nonIncremental) {
+    $rootScope.scrollWithBuffer = function(scrollToReadmarker, moreLines) {
         // First, get scrolling status *before* modification
         // This is required to determine where we were in the buffer pre-change
         var bl = document.getElementById('bufferlines');
@@ -443,11 +443,15 @@ weechat.controller('WeechatCtrl', ['$rootScope', '$scope', '$store', '$timeout',
             // Determine if we want to scroll at all
             // Give the check 3 pixels of slack so you don't have to hit
             // the exact spot. This fixes a bug in some browsers
-            if ((nonIncremental && sTop < sVal) || (Math.abs(sTop - sVal) < 3)) {
+            if (((scrollToReadmarker || moreLines) && sTop < sVal) || (Math.abs(sTop - sVal) < 3)) {
                 var readmarker = document.querySelector(".readmarker");
-                if (nonIncremental && readmarker) {
+                if (scrollToReadmarker && readmarker) {
                     // Switching channels, scroll to read marker
                     bl.scrollTop = readmarker.offsetTop - readmarker.parentElement.scrollHeight + readmarker.scrollHeight;
+                } else if (moreLines) {
+                    // We fetched more lines but the read marker is still out of view
+                    // Keep the scroll position constant
+                    bl.scrollTop = bl.scrollHeight - bl.clientHeight - sVal;
                 } else {
                     // New message, scroll with buffer (i.e. to bottom)
                     bl.scrollTop = bl.scrollHeight - bl.clientHeight;