Ensure interface gradually reduces visible buttons when viewport shrinks (#33477)

* Rewrite Measured to be a functional component

* Add tests to cover narrow viewports

* lint

* breakpoint is optional

* Cleanup

* Provide default value

* Fixup

* fix two snaps

* Update screenshot

* and the other one

* unfake CIDER

* Update snaps AGAIN

apps/web/playwright/e2e/composer/CIDER.spec.ts

@@ -77,6 +77,12 @@ test.describe("Composer", () => {
             await expect(page.locator(".mx_EventTile_body", { hasText: "😇" })).toBeVisible();
         });
 
+        test("renders in narrow viewports", { tag: "@screenshot" }, async ({ page, bot, app }) => {
+            // Shrink the viewport
+            await page.setViewportSize({ width: 500, height: 1080 });
+            await expect(app.getComposer()).toMatchScreenshot("narrow.png");
+        });
+
         test.describe("render emoji picker with larger viewport height", async () => {
             test.use({ viewport: { width: 1280, height: 720 } });
             test("render emoji picker", { tag: "@screenshot" }, async ({ page, app }) => {
@@ -201,12 +207,6 @@ test.describe("Composer", () => {
         });
 
         test("can paste a file", async ({ page, bot, app }) => {
-            // Set up a private room so we have another user to mention
-            await app.client.createRoom({
-                is_direct: true,
-                invite: [bot.credentials.userId],
-            });
-            await app.viewRoomByName("Bob");
             await app.composerDragAndPasteFile("room", getSampleFilePath("riot.png"), "image/png");
             await expect(page.locator(".mx_ImageBody")).toBeVisible();
         });

apps/web/playwright/e2e/composer/RTE.spec.ts

@@ -216,6 +216,12 @@ test.describe("Composer", () => {
             await expect(page.locator(".mx_ImageBody")).toBeVisible();
         });
 
+        test("renders in narrow viewports", { tag: "@screenshot" }, async ({ page, bot, app }) => {
+            // Shrink the viewport
+            await page.setViewportSize({ width: 750, height: 1080 });
+            await expect(page.locator(".mx_MessageComposer_wrapper")).toMatchScreenshot("narrow.png");
+        });
+
         test.describe("when Control+Enter is required to send", () => {
             test.beforeEach(async ({ app }) => {
                 await app.settings.setValue("MessageComposerInput.ctrlEnterToSend", null, SettingLevel.ACCOUNT, true);

apps/web/playwright/e2e/threads/threads.spec.ts

@@ -327,19 +327,19 @@ test.describe("Threads", () => {
 
     test.describe("with larger viewport", async () => {
         // Increase viewport size so that voice messages fit
-        test.use({ viewport: { width: 1280, height: 720 } });
+        test.use({ viewport: { width: 1440, height: 720 } });
 
         test.beforeEach(async ({ page }) => {
             // Increase right-panel size, so that voice messages fit
             await page.addInitScript(() => {
-                window.localStorage.setItem("mx_rhs_size", "600");
+                window.localStorage.setItem("mx_rhs_size", "700");
             });
         });
 
         test("can send voice messages", { tag: ["@no-firefox", "@no-webkit"] }, async ({ page, app, user }) => {
             // Increase right-panel size, so that voice messages fit
             await page.evaluate(() => {
-                window.localStorage.setItem("mx_rhs_size", "600");
+                window.localStorage.setItem("mx_rhs_size", "700");
             });
 
             const roomId = await app.client.createRoom({});

apps/web/src/components/structures/ThreadView.tsx

@@ -435,7 +435,7 @@ export default class ThreadView extends React.Component<IProps, IState> {
                             PosthogTrackers.trackInteraction("WebThreadViewBackButton", ev);
                         }}
                     >
-                        <Measured sensor={this.card} onMeasurement={this.onMeasurement} />
+                        <Measured breakpoint={400} sensor={this.card} onMeasurement={this.onMeasurement} />
                         <div className="mx_ThreadView_timelinePanelWrapper">{timeline}</div>
 
                         {ContentMessages.sharedInstance().getCurrentUploads(threadRelation).length > 0 && (

apps/web/src/components/views/elements/Measured.tsx

@@ -1,4 +1,5 @@
 /*
+Copyright (C) 2026 Element Creations Ltd
 Copyright 2024 New Vector Ltd.
 Copyright 2022 The Matrix.org Foundation C.I.C.
 
@@ -6,57 +7,65 @@ SPDX-License-Identifier: AGPL-3.0-only OR GPL-3.0-only OR LicenseRef-Element-Com
 Please see LICENSE files in the repository root for full details.
 */
 
-import React, { type RefObject } from "react";
+import { useEffect, useRef, type RefObject } from "react";
 
-import UIStore, { UI_EVENTS } from "../../../stores/UIStore";
+import UIStore from "../../../stores/UIStore";
+import { useEventEmitterState } from "../../../hooks/useEventEmitter";
 
 interface IProps {
+    /**
+     * Element to watch for resize changes on.
+     */
     sensor: RefObject<Element | null>;
-    breakpoint: number;
+    /**
-    onMeasurement(narrow: boolean): void;
+     * Minimum width of element to be considered full-size.
+     * Defaults to `500px`
+     */
+    breakpoint?: number;
+    /**
+     * Callback for when the narrowness property changes.
+     * @param narrow
+     * @returns
+     */
+    onMeasurement: (narrow: boolean) => void;
 }
 
-export default class Measured extends React.PureComponent<IProps> {
+let instanceCount = 0;
-    private static instanceCount = 0;
-    private readonly instanceId: number;
 
-    public static defaultProps = {
+/**
-        breakpoint: 500,
+ * This component can watch a single element for width changes, and will fire
+ * a callback if the width changes to be lower or higher than the `breakpoint`.
+ */
+export default function Measured({ sensor, breakpoint = 500, onMeasurement }: IProps): null {
+    const instanceIdRef = useRef(instanceCount++);
+    const instanceId = instanceIdRef.current;
+
+    useEffect(() => {
+        if (sensor.current) {
+            UIStore.instance.trackElementDimensions(`Measured${instanceId}`, sensor.current);
+        }
+
+        return () => {
+            UIStore.instance.stopTrackingElementDimensions(`Measured${instanceId}`);
         };
+    }, [sensor, instanceId]);
 
-    public constructor(props: IProps) {
+    const narrow = useEventEmitterState<boolean>(
-        super(props);
+        UIStore.instance,
-
+        `Measured${instanceId}`,
-        this.instanceId = Measured.instanceCount++;
+        (_type: unknown, entry: ResizeObserverEntry) => {
+            if (!entry) {
+                return false;
             }
+            // N.B there is only one `_type` of resize event.
+            return entry.contentRect.width <= breakpoint;
+        },
+    );
 
-    public componentDidMount(): void {
+    // Only fire when the state changes.
-        UIStore.instance.on(`Measured${this.instanceId}`, this.onResize);
+    useEffect(() => {
-    }
+        onMeasurement(narrow);
+    }, [onMeasurement, narrow]);
 
-    public componentDidUpdate(prevProps: Readonly<IProps>): void {
-        const previous = prevProps.sensor.current;
-        const current = this.props.sensor.current;
-        if (previous === current) return;
-        if (previous) {
-            UIStore.instance.stopTrackingElementDimensions(`Measured${this.instanceId}`);
-        }
-        if (current) {
-            UIStore.instance.trackElementDimensions(`Measured${this.instanceId}`, current);
-        }
-    }
-
-    public componentWillUnmount(): void {
-        UIStore.instance.off(`Measured${this.instanceId}`, this.onResize);
-        UIStore.instance.stopTrackingElementDimensions(`Measured${this.instanceId}`);
-    }
-
-    private onResize = (type: UI_EVENTS, entry: ResizeObserverEntry): void => {
-        if (type !== UI_EVENTS.Resize) return;
-        this.props.onMeasurement(entry.contentRect.width <= this.props.breakpoint);
-    };
-
-    public render(): React.ReactNode {
     return null;
-    }
 }