Move backdrop filter to a canvas based solution

res/css/structures/_LeftPanel.scss

@@ -43,7 +43,6 @@ $roomListCollapsedWidth: 68px;
     // Note: The 'room list' in this context is actually everything that isn't the tag
     // panel, such as the menu options, breadcrumbs, filtering, etc
     .mx_LeftPanel_roomListContainer {
-        background-color: $roomlist-bg-color;
         flex: 1 0 0;
         min-width: 0;
         // Create another flexbox (this time a column) for the room list components

res/css/structures/_MatrixChat.scss

@@ -35,6 +35,16 @@ limitations under the License.
     height: 100%;
 }
 
+.mx_BackdropPanel {
+    position: absolute;
+    top: 0;
+    left: 0;
+    width: 100%;
+    min-height: 100%;
+    z-index: 0;
+    opacity: .15;
+}
+
 .mx_MatrixToolbar {
     order: 1;
 

res/css/structures/_SpacePanel.scss

@@ -27,6 +27,7 @@ $activeBorderColor: $secondary-fg-color;
     background-color: $groupFilterPanel-bg-color;
     padding: 0;
     margin: 0;
+    position: relative;
 
     // Create another flexbox so the Panel fills the container
     display: flex;

res/themes/light/css/_mods.scss

@@ -4,27 +4,6 @@
 // set the user avatar (if any) as a background so
 // it can be blurred by the tag panel and room list
 
-@supports (backdrop-filter: none) {
-    .mx_LeftPanel {
-        background-image: var(--avatar-url, unset);
-        background-repeat: no-repeat;
-        background-size: cover;
-        background-position: left top;
-    }
-
-    .mx_GroupFilterPanel {
-        backdrop-filter: blur($groupFilterPanel-background-blur-amount);
-    }
-
-    .mx_SpacePanel {
-        backdrop-filter: blur($groupFilterPanel-background-blur-amount);
-    }
-
-    .mx_LeftPanel .mx_LeftPanel_roomListContainer {
-        backdrop-filter: blur($roomlist-background-blur-amount);
-    }
-}
-
 .mx_RoomSublist_showNButton {
     background-color: transparent !important;
 }

src/components/structures/BackdropPanel.tsx

@@ -0,0 +1,50 @@
+import React, { createRef } from "react";
+
+interface IProps {
+    width?: number;
+    height?: number;
+    backgroundImage?: ImageBitmap;
+    blur?: string;
+}
+
+
+export default class BackdropPanel extends React.PureComponent<IProps> {
+    private canvasRef: React.RefObject<HTMLCanvasElement> = createRef();
+    private ctx: CanvasRenderingContext2D;
+
+    static defaultProps = {
+        blur: "60px",
+    }
+
+    public componentDidMount() {
+        this.ctx = this.canvasRef.current.getContext("2d");
+    }
+
+    public componentDidUpdate() {
+        if (this.props.backgroundImage) {
+            requestAnimationFrame(this.refreshBackdropImage);
+        }
+    }
+
+    private refreshBackdropImage = (): void => {
+        const { width, height, backgroundImage } = this.props;
+        this.canvasRef.current.width = width;
+        this.canvasRef.current.height = height;
+
+        const destinationX = width - backgroundImage.width;
+        const destinationY = height - backgroundImage.height;
+
+        this.ctx.filter = `blur(${this.props.blur})`;
+        this.ctx.drawImage(
+            backgroundImage,
+            Math.min(destinationX, 0),
+            Math.min(destinationY, 0),
+            Math.max(width, backgroundImage.width),
+            Math.max(height, backgroundImage.height),
+        );
+    }
+
+    public render() {
+        return <canvas ref={this.canvasRef} className="mx_BackdropPanel" />;
+    }
+}

src/components/structures/LeftPanel.tsx

@@ -36,18 +36,18 @@ import SettingsStore from "../../settings/SettingsStore";
 import RoomListStore, { LISTS_UPDATE_EVENT } from "../../stores/room-list/RoomListStore";
 import IndicatorScrollbar from "../structures/IndicatorScrollbar";
 import AccessibleTooltipButton from "../views/elements/AccessibleTooltipButton";
-import { OwnProfileStore } from "../../stores/OwnProfileStore";
 import RoomListNumResults from "../views/rooms/RoomListNumResults";
 import LeftPanelWidget from "./LeftPanelWidget";
 import {replaceableComponent} from "../../utils/replaceableComponent";
-import {mediaFromMxc} from "../../customisations/Media";
 import SpaceStore, {UPDATE_SELECTED_SPACE} from "../../stores/SpaceStore";
 import { getKeyBindingsManager, RoomListAction } from "../../KeyBindingsManager";
 import UIStore from "../../stores/UIStore";
+import BackdropPanel from "./BackdropPanel";
 
 interface IProps {
     isMinimized: boolean;
     resizeNotifier: ResizeNotifier;
+    backgroundImage?: ImageBitmap;
 }
 
 interface IState {
@@ -85,16 +85,14 @@ export default class LeftPanel extends React.Component<IProps, IState> {
 
         BreadcrumbsStore.instance.on(UPDATE_EVENT, this.onBreadcrumbsUpdate);
         RoomListStore.instance.on(LISTS_UPDATE_EVENT, this.onBreadcrumbsUpdate);
-        OwnProfileStore.instance.on(UPDATE_EVENT, this.onBackgroundImageUpdate);
         SpaceStore.instance.on(UPDATE_SELECTED_SPACE, this.updateActiveSpace);
-        this.bgImageWatcherRef = SettingsStore.watchSetting(
-            "RoomList.backgroundImage", null, this.onBackgroundImageUpdate);
         this.groupFilterPanelWatcherRef = SettingsStore.watchSetting("TagPanel.enableTagPanel", null, () => {
             this.setState({showGroupFilterPanel: SettingsStore.getValue("TagPanel.enableTagPanel")});
         });
     }
 
     public componentDidMount() {
+        UIStore.instance.trackElementDimensions("LeftPanel", this.ref.current);
         UIStore.instance.trackElementDimensions("ListContainer", this.listContainerRef.current);
         UIStore.instance.on("ListContainer", this.refreshStickyHeaders);
         // Using the passive option to not block the main thread
@@ -104,10 +102,8 @@ export default class LeftPanel extends React.Component<IProps, IState> {
 
     public componentWillUnmount() {
         SettingsStore.unwatchSetting(this.groupFilterPanelWatcherRef);
-        SettingsStore.unwatchSetting(this.bgImageWatcherRef);
         BreadcrumbsStore.instance.off(UPDATE_EVENT, this.onBreadcrumbsUpdate);
         RoomListStore.instance.off(LISTS_UPDATE_EVENT, this.onBreadcrumbsUpdate);
-        OwnProfileStore.instance.off(UPDATE_EVENT, this.onBackgroundImageUpdate);
         SpaceStore.instance.off(UPDATE_SELECTED_SPACE, this.updateActiveSpace);
         UIStore.instance.stopTrackingElementDimensions("ListContainer");
         UIStore.instance.removeListener("ListContainer", this.refreshStickyHeaders);
@@ -144,23 +140,6 @@ export default class LeftPanel extends React.Component<IProps, IState> {
         }
     };
 
-    private onBackgroundImageUpdate = () => {
-        // Note: we do this in the LeftPanel as it uses this variable most prominently.
-        const avatarSize = 32; // arbitrary
-        let avatarUrl = OwnProfileStore.instance.getHttpAvatarUrl(avatarSize);
-        const settingBgMxc = SettingsStore.getValue("RoomList.backgroundImage");
-        if (settingBgMxc) {
-            avatarUrl = mediaFromMxc(settingBgMxc).getSquareThumbnailHttp(avatarSize);
-        }
-
-        const avatarUrlProp = `url(${avatarUrl})`;
-        if (!avatarUrl) {
-            document.body.style.removeProperty("--avatar-url");
-        } else if (document.body.style.getPropertyValue("--avatar-url") !== avatarUrlProp) {
-            document.body.style.setProperty("--avatar-url", avatarUrlProp);
-        }
-    };
-
     private handleStickyHeaders(list: HTMLDivElement) {
         if (this.isDoingStickyHeaders) return;
         this.isDoingStickyHeaders = true;
@@ -453,8 +432,15 @@ export default class LeftPanel extends React.Component<IProps, IState> {
             "mx_AutoHideScrollbar",
         );
 
+        const panelDimensions = UIStore.instance.getElementDimensions("LeftPanel");
+
         return (
             <div className={containerClasses} ref={this.ref}>
+                <BackdropPanel
+                    backgroundImage={this.props.backgroundImage}
+                    width={panelDimensions?.width}
+                    height={panelDimensions?.height}
+                />
                 {leftLeftPanel}
                 <aside className="mx_LeftPanel_roomListContainer">
                     {this.renderHeader()}

src/components/structures/LoggedInView.tsx

@@ -59,6 +59,10 @@ import {replaceableComponent} from "../../utils/replaceableComponent";
 import CallHandler, { CallHandlerEvent } from '../../CallHandler';
 import { MatrixCall } from 'matrix-js-sdk/src/webrtc/call';
 import AudioFeedArrayForCall from '../views/voip/AudioFeedArrayForCall';
+import { OwnProfileStore } from '../../stores/OwnProfileStore';
+import { UPDATE_EVENT } from "../../stores/AsyncStore";
+import { mediaFromMxc } from "../../customisations/Media";
+
 
 // We need to fetch each pinned message individually (if we don't already have it)
 // so each pinned message may trigger a request. Limit the number per room for sanity.
@@ -120,6 +124,7 @@ interface IState {
     usageLimitEventTs?: number;
     useCompactLayout: boolean;
     activeCalls: Array<MatrixCall>;
+    backgroundImage?: ImageBitmap;
 }
 
 /**
@@ -198,6 +203,8 @@ class LoggedInView extends React.Component<IProps, IState> {
         this.resizer = this._createResizer();
         this.resizer.attach();
         this._loadResizerPreferences();
+
+        OwnProfileStore.instance.on(UPDATE_EVENT, this.refreshBackgroundImage);
     }
 
     componentWillUnmount() {
@@ -206,10 +213,17 @@ class LoggedInView extends React.Component<IProps, IState> {
         this._matrixClient.removeListener("accountData", this.onAccountData);
         this._matrixClient.removeListener("sync", this.onSync);
         this._matrixClient.removeListener("RoomState.events", this.onRoomStateEvents);
+        OwnProfileStore.instance.off(UPDATE_EVENT, this.refreshBackgroundImage);
         SettingsStore.unwatchSetting(this.compactLayoutWatcherRef);
         this.resizer.detach();
     }
 
+    private refreshBackgroundImage = async (): Promise<void> => {
+        this.setState({
+            backgroundImage: await OwnProfileStore.instance.getAvatarBitmap(),
+        });
+    }
+
     private onCallsChanged = () => {
         this.setState({
             activeCalls: CallHandler.sharedInstance().getAllActiveCalls(),
@@ -633,10 +647,13 @@ class LoggedInView extends React.Component<IProps, IState> {
                 >
                     <ToastContainer />
                     <div ref={this._resizeContainer} className={bodyClasses}>
-                        { SettingsStore.getValue("feature_spaces") ? <SpacePanel /> : null }
+                        { SettingsStore.getValue("feature_spaces")
+                            ? <SpacePanel backgroundImage={this.state.backgroundImage} />
+                            : null }
                         <LeftPanel
                             isMinimized={this.props.collapseLhs || false}
                             resizeNotifier={this.props.resizeNotifier}
+                            backgroundImage={this.state.backgroundImage}
                         />
                         <ResizeHandle />
                         { pageElement }

src/components/views/spaces/SpacePanel.tsx

@@ -14,7 +14,7 @@ See the License for the specific language governing permissions and
 limitations under the License.
 */
 
-import React, { Dispatch, ReactNode, SetStateAction, useEffect, useState } from "react";
+import React, { Dispatch, ReactNode, SetStateAction, useEffect, useRef, useState } from "react";
 import { DragDropContext, Droppable, Draggable } from "react-beautiful-dnd";
 import classNames from "classnames";
 import { Room } from "matrix-js-sdk/src/models/room";
@@ -43,6 +43,8 @@ import { Key } from "../../../Keyboard";
 import { RoomNotificationStateStore } from "../../../stores/notifications/RoomNotificationStateStore";
 import { NotificationState } from "../../../stores/notifications/NotificationState";
 import SettingsStore from "../../../settings/SettingsStore";
+import BackdropPanel from "../../structures/BackdropPanel";
+import UIStore from "../../../stores/UIStore";
 
 interface IButtonProps {
     space?: Room;
@@ -178,7 +180,11 @@ const InnerSpacePanel = React.memo<IInnerSpacePanelProps>(({ children, isPanelCo
     </div>;
 });
 
-const SpacePanel = () => {
+interface IProps {
+    backgroundImage?: ImageBitmap;
+}
+
+const SpacePanel = (props: IProps) => {
     // We don't need the handle as we position the menu in a constant location
     // eslint-disable-next-line @typescript-eslint/no-unused-vars
     const [menuDisplayed, handle, openMenu, closeMenu] = useContextMenu<void>();
@@ -261,6 +267,15 @@ const SpacePanel = () => {
         openMenu();
     };
 
+    const ref: React.RefObject<HTMLUListElement> = useRef(null);
+    useEffect(() => {
+        UIStore.instance.trackElementDimensions("SpacePanel", ref.current);
+        return () => {
+            UIStore.instance.stopTrackingElementDimensions("SpacePanel");
+        }
+    }, []);
+    const panelDimensions = UIStore.instance.getElementDimensions("SpacePanel");
+
     return (
         <DragDropContext onDragEnd={result => {
             if (!result.destination) return; // dropped outside the list
@@ -271,7 +286,13 @@ const SpacePanel = () => {
                     <ul
                         className={classNames("mx_SpacePanel", { collapsed: isPanelCollapsed })}
                         onKeyDown={onKeyDownHandler}
+                        ref={ref}
                     >
+                        <BackdropPanel
+                            backgroundImage={props.backgroundImage}
+                            width={panelDimensions?.width}
+                            height={panelDimensions?.height}
+                        />
                         <Droppable droppableId="top-level-spaces">
                             {(provided, snapshot) => (
                                 <AutoHideScrollbar

src/stores/OwnProfileStore.ts

@@ -23,6 +23,7 @@ import { throttle } from "lodash";
 import { MatrixClientPeg } from "../MatrixClientPeg";
 import { _t } from "../languageHandler";
 import {mediaFromMxc} from "../customisations/Media";
+import SettingsStore from "../settings/SettingsStore";
 
 interface IState {
     displayName?: string;
@@ -137,6 +138,22 @@ export class OwnProfileStore extends AsyncStoreWithClient<IState> {
         await this.updateState({displayName: profileInfo.displayname, avatarUrl: profileInfo.avatar_url});
     };
 
+    public async getAvatarBitmap(avatarSize = 32): Promise<ImageBitmap> {
+        let avatarUrl = this.getHttpAvatarUrl(avatarSize);
+        const settingBgMxc = SettingsStore.getValue("RoomList.backgroundImage");
+        if (settingBgMxc) {
+            avatarUrl = mediaFromMxc(settingBgMxc).getSquareThumbnailHttp(avatarSize);
+        }
+
+        if (avatarUrl) {
+            const response = await fetch(avatarUrl);
+            const blob = await response.blob();
+            return await createImageBitmap(blob);
+        } else {
+            return null;
+        }
+    }
+
     private onStateEvents = throttle(async (ev: MatrixEvent) => {
         const myUserId = MatrixClientPeg.get().getUserId();
         if (ev.getType() === 'm.room.member' && ev.getSender() === myUserId && ev.getStateKey() === myUserId) {