Merge pull request #5697 from matrix-org/travis/fix-tetris

Fix tetris effect (holes) in read receipts

src/Velociraptor.js

@@ -118,25 +118,10 @@ export default class Velociraptor extends React.Component {
                     domNode.style.visibility = restingStyle.visibility;
                 });
 
-            /*
-            console.log("enter:",
-                        JSON.stringify(transitionOpts[i-1]),
-                        "->",
-                        JSON.stringify(restingStyle));
-            */
-        } else if (node === null) {
-            // Velocity stores data on elements using the jQuery .data()
-            // method, and assumes you'll be using jQuery's .remove() to
-            // remove the element, but we don't use jQuery, so we need to
-            // blow away the element's data explicitly otherwise it will leak.
-            // This uses Velocity's internal jQuery compatible wrapper.
-            // See the bug at
-            // https://github.com/julianshapiro/velocity/issues/300
-            // and the FAQ entry, "Preventing memory leaks when
-            // creating/destroying large numbers of elements"
-            // (https://github.com/julianshapiro/velocity/issues/47)
-            const domNode = ReactDom.findDOMNode(this.nodes[k]);
-            if (domNode) Velocity.Utilities.removeData(domNode);
+            // console.log("enter:",
+            //             JSON.stringify(transitionOpts[i-1]),
+            //             "->",
+            //             JSON.stringify(restingStyle));
         }
         this.nodes[k] = node;
     }

src/components/views/rooms/ReadReceiptMarker.js

@@ -32,7 +32,7 @@ try {
 } catch (e) {
 }
 
-export default class ReadReceiptMarker extends React.Component {
+export default class ReadReceiptMarker extends React.PureComponent {
     static propTypes = {
         // the RoomMember to show the RR for
         member: PropTypes.object,
@@ -155,7 +155,15 @@ export default class ReadReceiptMarker extends React.Component {
 
         // then shift to the rightmost column,
         // and then it will drop down to its resting position
-        startStyles.push({ top: startTopOffset+'px', left: '0px' });
+        //
+        // XXX: We use a fractional left value to trick velocity-animate into actually animating.
+        // This is a very annoying bug where if it thinks there's no change to `left` then it'll
+        // skip applying it, thus making our read receipt at +14px instead of +0px like it
+        // should be. This does cause a tiny amount of drift for read receipts, however with a
+        // value so small it's not perceived by a user.
+        // Note: Any smaller values (or trying to interchange units) might cause read receipts to
+        // fail to fall down or cause gaps.
+        startStyles.push({ top: startTopOffset+'px', left: '0.001px' });
         enterTransitionOpts.push({
             duration: bounce ? Math.min(Math.log(Math.abs(startTopOffset)) * 200, 3000) : 300,
             easing: bounce ? 'easeOutBounce' : 'easeOutCubic',