From 146d832e19591b0e85fee5cb4286a458d8781393 Mon Sep 17 00:00:00 2001
From: James Allen <james@sharelatex.com>
Date: Wed, 6 Aug 2014 13:10:41 +0100
Subject: [PATCH] Keep apparent scroll position fixed when changes are made
 offscreen

---
 lib/ace/virtual_renderer.js | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/lib/ace/virtual_renderer.js b/lib/ace/virtual_renderer.js
index dfb435be..60b7b779 100644
--- a/lib/ace/virtual_renderer.js
+++ b/lib/ace/virtual_renderer.js
@@ -809,6 +809,15 @@ var VirtualRenderer = function(container, theme) {
             changes & this.CHANGE_H_SCROLL
         ) {
             changes |= this.$computeLayerConfig();
+            // If a change is made offscreen and wrapMode is on, then the onscreen
+            // lines may have been pushed down. If so, the first screen row will not
+            // have changed, but the first actual row will. In that case, adjust 
+            // scrollTop so that the cursor and onscreen content stays in the same place.
+            if (config.firstRow != this.layerConfig.firstRow && config.firstRowScreen == this.layerConfig.firstRowScreen) {
+                this.scrollTop = this.scrollTop + (config.firstRow - this.layerConfig.firstRow) * this.lineHeight;
+                changes = changes | this.CHANGE_SCROLL;
+                changes |= this.$computeLayerConfig();
+            }
             config = this.layerConfig;
             // update scrollbar first to not lose scroll position when gutter calls resize
             this.$updateScrollBarV();