From f9d2d45b242c1035a68ec3961ca05eafdad39aa2 Mon Sep 17 00:00:00 2001
From: Bruno Windels <brunow@matrix.org>
Date: Tue, 3 Mar 2020 15:42:22 +0100
Subject: [PATCH 1/3] use relative scrolling to compensate when changing height

---
 src/components/structures/ScrollPanel.js | 14 ++++++--------
 1 file changed, 6 insertions(+), 8 deletions(-)

diff --git a/src/components/structures/ScrollPanel.js b/src/components/structures/ScrollPanel.js
index 5121dd3f9d..72d5330451 100644
--- a/src/components/structures/ScrollPanel.js
+++ b/src/components/structures/ScrollPanel.js
@@ -705,17 +705,15 @@ export default createReactClass({
             // the currently filled piece of the timeline
             if (trackedNode) {
                 const oldTop = trackedNode.offsetTop;
-                // changing the height might change the scrollTop
-                // if the new height is smaller than the scrollTop.
-                // We calculate the diff that needs to be applied
-                // ourselves, so be sure to measure the
-                // scrollTop before changing the height.
-                const preexistingScrollTop = sn.scrollTop;
                 itemlist.style.height = `${newHeight}px`;
                 const newTop = trackedNode.offsetTop;
                 const topDiff = newTop - oldTop;
-                sn.scrollTop = preexistingScrollTop + topDiff;
-                debuglog("updateHeight to", {newHeight, topDiff, preexistingScrollTop});
+                // important to scroll by a relative amount as
+                // reading scrollTop and then setting it might
+                // yield out of date values and cause a jump
+                // when setting it
+                sn.scrollBy(0, topDiff);
+                debuglog("updateHeight to", {newHeight, topDiff});
             }
         }
     },

From 223956a206f217e4d6ed5e2abfb1b0558b336414 Mon Sep 17 00:00:00 2001
From: Bruno Windels <brunow@matrix.org>
Date: Tue, 3 Mar 2020 15:42:44 +0100
Subject: [PATCH 2/3] add comment how offset from bottom is calculated

---
 src/components/structures/ScrollPanel.js | 1 +
 1 file changed, 1 insertion(+)

diff --git a/src/components/structures/ScrollPanel.js b/src/components/structures/ScrollPanel.js
index 72d5330451..548dd70748 100644
--- a/src/components/structures/ScrollPanel.js
+++ b/src/components/structures/ScrollPanel.js
@@ -765,6 +765,7 @@ export default createReactClass({
     },
 
     _topFromBottom(node) {
+        // current capped height - distance from top = distance from bottom of container to top of tracked element
         return this._itemlist.current.clientHeight - node.offsetTop;
     },
 

From 3e39cebb8f18006a5e20a44a45f3e21aaf59b17c Mon Sep 17 00:00:00 2001
From: Bruno Windels <brunow@matrix.org>
Date: Tue, 3 Mar 2020 15:44:59 +0100
Subject: [PATCH 3/3] also use relative scrolling when eh ... doing relative
 scrolling

---
 src/components/structures/ScrollPanel.js | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/components/structures/ScrollPanel.js b/src/components/structures/ScrollPanel.js
index 548dd70748..b81b3ebede 100644
--- a/src/components/structures/ScrollPanel.js
+++ b/src/components/structures/ScrollPanel.js
@@ -523,7 +523,7 @@ export default createReactClass({
     scrollRelative: function(mult) {
         const scrollNode = this._getScrollNode();
         const delta = mult * scrollNode.clientHeight * 0.5;
-        scrollNode.scrollTop = scrollNode.scrollTop + delta;
+        scrollNode.scrollBy(0, delta);
         this._saveScrollState();
     },