Merge pull request #4166 from matrix-org/bwindels/relativescrolling

Adjust scroll offset with relative scrolling
matrix-org · Mar 3, 2020 · 72af620 · 72af620
2 parents b23eaa1 + 3e39ceb
commit 72af620
Showing 1 changed file with 8 additions and 9 deletions.
diff --git 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();
     },
 
@@ -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+                // yield out of date values and cause a jump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});
             }
         }
     },
@@ -767,6 +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;
     },