Disable animations for users that prefer reduced motion

src/room/InCallView.tsx

@@ -60,6 +60,7 @@ import { useAudioOutputDevice } from "../video-grid/useAudioOutputDevice";
 import { widget, ElementWidgetActions } from "../widget";
 import { useJoinRule } from "./useJoinRule";
 import { useUrlParams } from "../UrlParams";
+import { usePrefersReducedMotion } from "../usePrefersReducedMotion";
 
 const canScreenshare = "getDisplayMedia" in (navigator.mediaDevices ?? {});
 // There is currently a bug in Safari our our code with cloning and sending MediaStreams
@@ -265,6 +266,8 @@ export function InCallView({
     []
   );
 
+  const prefersReducedMotion = usePrefersReducedMotion();
+
   const renderContent = (): JSX.Element => {
     if (items.length === 0) {
       return (
@@ -292,7 +295,11 @@ export function InCallView({
     }
 
     return (
-      <VideoGrid items={items} layout={layout} disableAnimations={isSafari}>
+      <VideoGrid
+        items={items}
+        layout={layout}
+        disableAnimations={prefersReducedMotion || isSafari}
+      >
         {({
           item,
           ...rest

src/room/PTTButton.tsx

@@ -22,6 +22,7 @@ import styles from "./PTTButton.module.css";
 import { ReactComponent as MicIcon } from "../icons/Mic.svg";
 import { useEventTarget } from "../useEvents";
 import { Avatar } from "../Avatar";
+import { usePrefersReducedMotion } from "../usePrefersReducedMotion";
 
 interface Props {
   enabled: boolean;
@@ -159,8 +160,14 @@ export const PTTButton: React.FC<Props> = ({
   // TODO: We will need to disable this for a global PTT hotkey to work
   useEventTarget(window, "blur", unhold);
 
+  const prefersReducedMotion = usePrefersReducedMotion();
   const { shadow } = useSpring({
-    shadow: (Math.max(activeSpeakerVolume, -70) + 70) * 0.6,
+    immediate: prefersReducedMotion,
+    shadow: prefersReducedMotion
+      ? activeSpeakerUserId
+        ? 17
+        : 0
+      : (Math.max(activeSpeakerVolume, -70) + 70) * 0.6,
     config: {
       clamp: true,
       tension: 300,

src/usePrefersReducedMotion.ts

@@ -0,0 +1,42 @@
+/*
+Copyright 2022 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 { useCallback, useRef, useState } from "react";
+
+import { useEventTarget } from "./useEvents";
+
+/**
+ * @returns Whether the user has requested reduced motion.
+ */
+export const usePrefersReducedMotion = () => {
+  const mediaQuery = useRef<MediaQueryList>();
+  if (mediaQuery.current === undefined)
+    mediaQuery.current = matchMedia("(prefers-reduced-motion)");
+
+  const [prefersReducedMotion, setPrefersReducedMotion] = useState(
+    mediaQuery.current.matches
+  );
+  useEventTarget(
+    mediaQuery.current!,
+    "change",
+    useCallback(
+      () => setPrefersReducedMotion(mediaQuery.current!.matches),
+      [setPrefersReducedMotion]
+    )
+  );
+
+  return prefersReducedMotion;
+};