fix(linux/flatpak): ensure emojis are rendered correctly on every launch

src/app/system.utils.ts

@@ -146,6 +146,7 @@ export async function clearFlatpakFontConfigCache() {
 	}
 
 	try {
+		console.debug('Clearing Flatpak font config cache...')
 		// Note: clearing with "fc-cache" command did not help with the issue (was tested with many users and colleagues)
 		await rm(path.join(process.env.XDG_CACHE_HOME, 'fontconfig'), { recursive: true, force: true })
 	} catch (error) {

src/main.js

@@ -18,7 +18,7 @@ const { triggerDownloadUrl } = require('./app/downloads.ts')
 const { setupReleaseNotificationScheduler, checkForUpdate } = require('./app/githubRelease.service.ts')
 const { initLaunchAtStartupListener } = require('./app/launchAtStartup.config.ts')
 const { runMigrations } = require('./app/migration.service.ts')
-const { systemInfo, isLinux, isMac, isWindows, isSameExecution, isSquirrel, relaunchApp } = require('./app/system.utils.ts')
+const { systemInfo, isLinux, isMac, isWindows, isSameExecution, isSquirrel, relaunchApp, clearFlatpakFontConfigCache } = require('./app/system.utils.ts')
 const { applyTheme } = require('./app/theme.config.ts')
 const { buildTitle } = require('./app/utils.ts')
 const { enableWebRequestInterceptor, disableWebRequestInterceptor } = require('./app/webRequestInterceptor.js')
@@ -92,6 +92,7 @@ ipcMain.on('app:grantUserGesturedPermission', (event, id) => {
 	return event.sender.executeJavaScript(`document.getElementById('${id}')?.click()`, true)
 })
 ipcMain.on('app:toggleDevTools', (event) => event.sender.toggleDevTools())
+ipcMain.on('app:clearFlatpakFontConfigCache', async () => clearFlatpakFontConfigCache())
 ipcMain.handle('app:anything', () => { /* Put any code here to run it from UI */ })
 ipcMain.on('app:openChromeWebRtcInternals', () => openChromeWebRtcInternals())
 ipcMain.handle('app:update:check', async () => await checkForUpdate({ forceRequest: true }))

src/preload.js

@@ -98,7 +98,7 @@
 	 * Set an application config value by key
 	 *
 	 * @param {string} key - Config key
 	 * @param {any} [value] - Config value
 	 * @return {Promise<void>}
 	 */
 	setAppConfig: (key, value) => ipcRenderer.invoke('app:config:set', key, value),
@@ -125,10 +125,14 @@
 	 * Open developer tools
 	 */
 	toggleDevTools: () => ipcRenderer.send('app:toggleDevTools'),
+	/**
+	 * Clear Flatpak fontconfig cache
+	 */
+	clearFlatpakFontConfigCache: () => ipcRenderer.send('app:clearFlatpakFontConfigCache'),
 	/**
 	 * Invoke app:anything
 	 *
 	 * @param {...any} args - Arguments
 	 */
 	invokeAnything: (...args) => ipcRenderer.invoke('app:anything', ...args),
 	/**

src/welcome/ensureFlatpakEmojiFontRendering.ts

@@ -0,0 +1,105 @@
+/*!
+ * SPDX-FileCopyrightText: 2026 Nextcloud GmbH and Nextcloud contributors
+ * SPDX-License-Identifier: AGPL-3.0-or-later
+ */
+
+import { getBuilder } from '@nextcloud/browser-storage'
+
+/**
+ * Cool down time after the last attempt to clear the Flatpak font config cache preventing infinite loop in case of failed fix
+ */
+const FLATPAK_FONT_CONFIG_CACHE_CLEAR_COOL_DOWN = 24 * 60 * 60 * 1000 // 24h
+
+const LAST_FLATPAK_FONT_CONFIG_CACHE_CLEAR_KEY = 'lastFlatpakFontConfigCacheClear'
+
+/**
+ * Ensure there is no emoji rendering issue in Flatpak installation resulting in emojis being rendered as text instead of colored.
+ * If there is, clear the Flatpak font config cache and relaunch the app.
+ */
+export async function ensureFlatpakEmojiFontRendering() {
+	// Flatpak specific issue only
+	if (!window.systemInfo.isFlatpak) {
+		return
+	}
+
+	// No issues - nothing to fix
+	if (!hasEmojiRenderingIssue()) {
+		return
+	}
+
+	// Prevent the relaunch loop when there is an issue but it is not solved by clearing the cache and relaunch
+	const browserStorage = getBuilder('talk-desktop').persist().build()
+	const lastFontconfigCacheClear = browserStorage.getItem(LAST_FLATPAK_FONT_CONFIG_CACHE_CLEAR_KEY)
+
+	if (lastFontconfigCacheClear && (Date.now() - parseInt(lastFontconfigCacheClear)) < FLATPAK_FONT_CONFIG_CACHE_CLEAR_COOL_DOWN) {
+		console.warn('Emoji rendering issue detected, but font config cache was cleared recently. Probably the issue is not solvable by clearing the cache...')
+		return
+	}
+
+	browserStorage.setItem(LAST_FLATPAK_FONT_CONFIG_CACHE_CLEAR_KEY, Date.now().toString())
+
+	await window.TALK_DESKTOP.clearFlatpakFontConfigCache()
+	await window.TALK_DESKTOP.relaunch()
+}
+
+/**
+ * Check whether there is an emoji rendering issue resulting in emojis being rendered as text instead of colored images
+ * by rendering an emoji on a canvas and checking how colorful it is.
+ * The check cost is around 40ms.
+ */
+export function hasEmojiRenderingIssue(): boolean {
+	const EMOJI = '😅'
+	// Uncomment for testing of forced text emoji rendering
+	// const EMOJI = '😅\uFE0E'
+
+	// Same as in EmojiPicker
+	const FONT_FAMILY = '"Segoe UI Emoji","Segoe UI Symbol","Segoe UI","Apple Color Emoji","Twemoji Mozilla","Noto Color Emoji","EmojiOne Color","Android Emoji"'
+	const FONT_SIZE = 15
+	const WIDTH = 20
+	const HEIGHT = 20
+
+	/**
+	 * How much colored an emoji must be to consider it successfully colored.
+	 * On testing, monochrome text emoji is always 0.0 and colored emoji is usually 0.4..0.6 with bright yellow Noto Color Emojis
+	 * Only very gray emojis like 😶‍🌫️ has low chroma and it is still >0.11
+	 */
+	const CHROMA_THRESHOLD = 0.1
+
+	const canvas = document.createElement('canvas')
+	canvas.width = WIDTH
+	canvas.height = HEIGHT
+	// Uncomment for debugging
+	// document.body.appendChild(canvas)
+
+	const ctx = canvas.getContext('2d')!
+	ctx.fillStyle = '#000000'
+	ctx.font = `${FONT_SIZE}px ${FONT_FAMILY}`
+	ctx.textAlign = 'center'
+	ctx.fillText(EMOJI, WIDTH / 2, FONT_SIZE, WIDTH)
+
+	const { data } = ctx.getImageData(0, 0, WIDTH, HEIGHT)
+
+	const chroma = imageChroma(data)
+	console.debug('Flatpak emoji rendering test chroma:', chroma)
+
+	return chroma < CHROMA_THRESHOLD
+}
+
+/**
+ * Calculates the average chroma of the given pixel data, ignoring transparent parts
+ *
+ * @param pixels - RGBA pixel image data
+ */
+function imageChroma(pixels: Uint8ClampedArray): number {
+	let totalChroma = 0
+	let nonTransparentPixels = 0
+	for (let i = 0; i < pixels.length; i += 4) {
+		const [r, g, b, a] = [pixels[i]!, pixels[i + 1]!, pixels[i + 2]!, pixels[i + 3]!]
+		if (a === 0) {
+			continue
+		}
+		nonTransparentPixels += 1
+		totalChroma += Math.max(r, g, b) - Math.min(r, g, b)
+	}
+	return totalChroma / nonTransparentPixels / 255
+}

src/welcome/welcome.main.ts

@@ -8,6 +8,7 @@ import { refetchAppDataWithRetry } from '../app/appData.service.js'
 import { getAppConfigValue, initAppConfig, setAppConfigValue } from '../shared/appConfig.service.ts'
 import { initGlobals } from '../shared/globals/globals.js'
 import { applyAxiosInterceptors } from '../shared/setupWebPage.js'
+import { ensureFlatpakEmojiFontRendering } from './ensureFlatpakEmojiFontRendering.ts'
 
 import '@global-styles/dist/icons.css'
 
@@ -30,6 +31,8 @@ appData.restore()
 initGlobals()
 applyAxiosInterceptors()
 
+await ensureFlatpakEmojiFontRendering()
+
 if (appData.credentials) {
 	await window.TALK_DESKTOP.enableWebRequestInterceptor(appData.serverUrl, { credentials: appData.credentials })
 	await refetchAppDataWithRetry(appData)