enhance(frontend): テーマ切り替えのアニメーションをView Transitionに変更 (#15974)

* enhance(frontend): テーマ切り替えのアニメーションをView Transitionに変更

* fix lint

* fix: 切り替え時間を0.5sに

3 files changed, 86 insertions, 19 deletions

diff --git a/packages/frontend/src/components/MkFoldableSection.vue b/packages/frontend/src/components/MkFoldableSection.vue
index b9888d9b64..0fa7bea7ab 100644
--- a/packages/frontend/src/components/MkFoldableSection.vue
+++ b/packages/frontend/src/components/MkFoldableSection.vue
@@ -31,9 +31,10 @@ SPDX-License-Identifier: AGPL-3.0-only
 </template>
 
 <script lang="ts" setup>
-import { onMounted, ref, useTemplateRef, watch } from 'vue';
+import { onBeforeUnmount, onMounted, ref, useTemplateRef, watch } from 'vue';
 import { miLocalStorage } from '@/local-storage.js';
 import { prefer } from '@/preferences.js';
+import { globalEvents } from '@/events.js';
 import { getBgColor } from '@/utility/get-bg-color.js';
 
 const miLocalStoragePrefix = 'ui:folder:' as const;
@@ -83,8 +84,19 @@ function afterLeave(el: Element) {
 	el.style.height = '';
 }
 
+function updateBgColor() {
+	if (rootEl.value) {
+		parentBg.value = getBgColor(rootEl.value.parentElement);
+	}
+}
+
 onMounted(() => {
-	parentBg.value = getBgColor(rootEl.value?.parentElement);
+	updateBgColor();
+	globalEvents.on('themeChanging', updateBgColor);
+});
+
+onBeforeUnmount(() => {
+	globalEvents.off('themeChanging', updateBgColor);
 });
 </script>
 
diff --git a/packages/frontend/src/style.scss b/packages/frontend/src/style.scss
index 30936fbb10..12879e63b3 100644
--- a/packages/frontend/src/style.scss
+++ b/packages/frontend/src/style.scss
@@ -90,12 +90,49 @@ html {
 	}
 }
 
-html._themeChanging_ {
+html._themeChangingFallback_ {
 	&, * {
-		transition: background 1s ease, border 1s ease !important;
+		transition: background 0.5s ease, border 0.5s ease !important;
 	}
 }
 
+html._themeChanging_ {
+	view-transition-name: theme-changing;
+}
+
+html::view-transition-new(theme-changing) {
+	z-index: 4000001;
+	animation: themeChangingNew 0.5s ease;
+	animation-fill-mode: forwards;
+}
+
+html::view-transition-old(theme-changing) {
+	z-index: 4000000;
+	animation: themeChangingOld 0.5s ease;
+	animation-fill-mode: forwards;
+}
+
+@keyframes themeChangingNew {
+	0% {
+		opacity: 0;
+	}
+
+	100% {
+		opacity: 1;
+	}
+}
+
+@keyframes themeChangingOld {
+	0% {
+		opacity: 1;
+	}
+
+	100% {
+		opacity: 0;
+	}
+
+}
+
 html,
 body,
 #misskey_app {
diff --git a/packages/frontend/src/theme.ts b/packages/frontend/src/theme.ts
index 268f879d17..9562f69cf3 100644
--- a/packages/frontend/src/theme.ts
+++ b/packages/frontend/src/theme.ts
@@ -3,7 +3,7 @@
  * SPDX-License-Identifier: AGPL-3.0-only
  */
 
-import { ref } from 'vue';
+import { ref, nextTick } from 'vue';
 import tinycolor from 'tinycolor2';
 import lightTheme from '@@/themes/_light.json5';
 import darkTheme from '@@/themes/_dark.json5';
@@ -88,20 +88,7 @@ export async function removeTheme(theme: Theme): Promise<void> {
 	prefer.commit('themes', themes);
 }
 
-let timeout: number | null = null;
-
-export function applyTheme(theme: Theme, persist = true) {
-	if (timeout) window.clearTimeout(timeout);
-
-	window.document.documentElement.classList.add('_themeChanging_');
-
-	timeout = window.setTimeout(() => {
-		window.document.documentElement.classList.remove('_themeChanging_');
-
-		// 色計算など再度行えるようにクライアント全体に通知
-		globalEvents.emit('themeChanged');
-	}, 1000);
-
+function applyThemeInternal(theme: Theme, persist: boolean) {
 	const colorScheme = theme.base === 'dark' ? 'dark' : 'light';
 
 	window.document.documentElement.dataset.colorScheme = colorScheme;
@@ -139,6 +126,37 @@ export function applyTheme(theme: Theme, persist = true) {
 	globalEvents.emit('themeChanging');
 }
 
+let timeout: number | null = null;
+
+export function applyTheme(theme: Theme, persist = true) {
+	if (timeout) {
+		window.clearTimeout(timeout);
+		timeout = null;
+	}
+
+	if (window.document.startViewTransition != null && prefer.s.animation) {
+		window.document.documentElement.classList.add('_themeChanging_');
+		window.document.startViewTransition(async () => {
+			applyThemeInternal(theme, persist);
+			await nextTick();
+		}).finished.then(() => {
+			window.document.documentElement.classList.remove('_themeChanging_');
+			// 色計算など再度行えるようにクライアント全体に通知
+			globalEvents.emit('themeChanged');
+		});
+	} else {
+		// TODO: ViewTransition API が主要ブラウザで対応したら消す
+		window.document.documentElement.classList.add('_themeChangingFallback_');
+		timeout = window.setTimeout(() => {
+			window.document.documentElement.classList.remove('_themeChangingFallback_');
+			// 色計算など再度行えるようにクライアント全体に通知
+			globalEvents.emit('themeChanged');
+		}, 500);
+
+		applyThemeInternal(theme, persist);
+	}
+}
+
 export function compile(theme: Theme): Record<string, string> {
 	function getColor(val: string): tinycolor.Instance {
 		if (val[0] === '@') { // ref (prop)