Merge pull request #2629 from matrix-org/bwindels/lazyroomtilerendering

Improve room list rendering performance

src/components/structures/AutoHideScrollbar.js

@@ -114,10 +114,15 @@ export default class AutoHideScrollbar extends React.Component {
         }
     }
 
+    getScrollTop() {
+        return this.containerRef.scrollTop;
+    }
+
     render() {
         return (<div
                     ref={this._collectContainerRef}
                     className={["mx_AutoHideScrollbar", this.props.className].join(" ")}
+                    onScroll={this.props.onScroll}
                 >
             <div className="mx_AutoHideScrollbar_offset">
                 { this.props.children }

src/components/structures/IndicatorScrollbar.js

@@ -59,6 +59,10 @@ export default class IndicatorScrollbar extends React.Component {
         }
     }
 
+    getScrollTop() {
+        return this._autoHideScrollbar.getScrollTop();
+    }
+
     componentWillUnmount() {
         if (this._scrollElement) {
             this._scrollElement.removeEventListener("scroll", this.checkOverflow);

src/components/structures/RoomSubList.js

@@ -27,7 +27,8 @@ import IndicatorScrollbar from './IndicatorScrollbar';
 import { KeyCode } from '../../Keyboard';
 import { Group } from 'matrix-js-sdk';
 import PropTypes from 'prop-types';
-
+import RoomTile from "../views/rooms/RoomTile";
+import LazyRenderList from "../views/elements/LazyRenderList";
 
 // turn this on for drop & drag console debugging galore
 const debug = false;
@@ -60,6 +61,9 @@ const RoomSubList = React.createClass({
     getInitialState: function() {
         return {
             hidden: this.props.startAsHidden || false,
+            // some values to get LazyRenderList starting
+            scrollerHeight: 800,
+            scrollTop: 0,
         };
     },
 
@@ -134,9 +138,7 @@ const RoomSubList = React.createClass({
         this.setState(this.state);
     },
 
-    makeRoomTiles: function() {
-        const RoomTile = sdk.getComponent("rooms.RoomTile");
-        return this.props.list.map((room, index) => {
+    makeRoomTile: function(room) {
         return <RoomTile
             room={room}
             roomSubList={this}
@@ -151,7 +153,6 @@ const RoomSubList = React.createClass({
             incomingCall={null}
             onClick={this.onRoomTileClick}
         />;
-        });
     },
 
     _onNotifBadgeClick: function(e) {
@@ -270,6 +271,29 @@ const RoomSubList = React.createClass({
         if (this.refs.subList) {
             this.refs.subList.style.height = `${height}px`;
         }
+        this._updateLazyRenderHeight(height);
+    },
+
+    _updateLazyRenderHeight: function(height) {
+        this.setState({scrollerHeight: height});
+    },
+
+    _onScroll: function() {
+        this.setState({scrollTop: this.refs.scroller.getScrollTop()});
+    },
+
+    _getRenderItems: function() {
+        // try our best to not create a new array
+        // because LazyRenderList rerender when the items prop
+        // is not the same object as the previous value
+        const {list, extraTiles} = this.props;
+        if (!extraTiles || !extraTiles.length) {
+            return list;
+        }
+        if (!list || list.length) {
+            return extraTiles;
+        }
+        return list.concat(extraTiles);
     },
 
     render: function() {
@@ -287,12 +311,15 @@ const RoomSubList = React.createClass({
                     {this._getHeaderJsx(isCollapsed)}
                 </div>;
             } else {
-                const tiles = this.makeRoomTiles();
-                tiles.push(...this.props.extraTiles);
                 return <div ref="subList" className={subListClasses}>
                     {this._getHeaderJsx(isCollapsed)}
-                    <IndicatorScrollbar ref="scroller" className="mx_RoomSubList_scroll">
-                        { tiles }
+                    <IndicatorScrollbar ref="scroller" className="mx_RoomSubList_scroll" onScroll={ this._onScroll }>
+                        <LazyRenderList
+                            scrollTop={this.state.scrollTop }
+                            height={ this.state.scrollerHeight }
+                            renderItem={ this.makeRoomTile }
+                            itemHeight={34}
+                            items={this._getRenderItems()} />
                     </IndicatorScrollbar>
                 </div>;
             }

src/components/views/elements/LazyRenderList.js

@@ -0,0 +1,92 @@
+/*
+Copyright 2019 New Vector Ltd
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+import React from "react";
+
+const OVERFLOW_ITEMS = 20;
+const OVERFLOW_MARGIN = 5;
+
+class ItemRange {
+    constructor(topCount, renderCount, bottomCount) {
+        this.topCount = topCount;
+        this.renderCount = renderCount;
+        this.bottomCount = bottomCount;
+    }
+
+    contains(range) {
+        return range.topCount >= this.topCount &&
+            (range.topCount + range.renderCount) <= (this.topCount + this.renderCount);
+    }
+
+    expand(amount) {
+        const topGrow = Math.min(amount, this.topCount);
+        const bottomGrow = Math.min(amount, this.bottomCount);
+        return new ItemRange(
+            this.topCount - topGrow,
+            this.renderCount + topGrow + bottomGrow,
+            this.bottomCount - bottomGrow,
+        );
+    }
+}
+
+export default class LazyRenderList extends React.Component {
+    constructor(props) {
+        super(props);
+        const renderRange = LazyRenderList.getVisibleRangeFromProps(props).expand(OVERFLOW_ITEMS);
+        this.state = {renderRange};
+    }
+
+    static getVisibleRangeFromProps(props) {
+        const {items, itemHeight, scrollTop, height} = props;
+        const length = items ? items.length : 0;
+        const topCount = Math.max(0, Math.floor(scrollTop / itemHeight));
+        const itemsAfterTop = length - topCount;
+        const renderCount = Math.min(Math.ceil(height / itemHeight), itemsAfterTop);
+        const bottomCount = itemsAfterTop - renderCount;
+        return new ItemRange(topCount, renderCount, bottomCount);
+    }
+
+    componentWillReceiveProps(props) {
+        const state = this.state;
+        const range = LazyRenderList.getVisibleRangeFromProps(props);
+        // only update state if the new range isn't contained by the old anymore
+        if (!state.renderRange || !state.renderRange.contains(range.expand(OVERFLOW_MARGIN))) {
+            this.setState({renderRange: range.expand(OVERFLOW_ITEMS)});
+        }
+    }
+
+    shouldComponentUpdate(nextProps, nextState) {
+        const itemsChanged = nextProps.items !== this.props.items;
+        const rangeChanged = nextState.renderRange !== this.state.renderRange;
+        return itemsChanged || rangeChanged;
+    }
+
+    render() {
+        const {itemHeight, items, renderItem} = this.props;
+
+        const {renderRange} = this.state;
+        const paddingTop = renderRange.topCount * itemHeight;
+        const paddingBottom = renderRange.bottomCount * itemHeight;
+        const renderedItems = (items || []).slice(
+            renderRange.topCount,
+            renderRange.topCount + renderRange.renderCount,
+        );
+
+        return (<div style={{paddingTop: `${paddingTop}px`, paddingBottom: `${paddingBottom}px`}}>
+            { renderedItems.map(renderItem) }
+        </div>);
+    }
+}