From ef38c975b994bb131eb327454c836c0ea84efd20 Mon Sep 17 00:00:00 2001
From: MaxsTechReview <maxjividen@gmail.com>
Date: Wed, 7 Oct 2026 02:23:27 -0400
Subject: [PATCH] Draw Steam's CJK and Thai text with the device's fonts (#374)

Steam ships no CJK font and the rootfs only has DejaVu, so a phone set to
Chinese, Japanese or Korean got Steam in that language with every character
drawn as a box. Bind Android's /system/fonts into the guest, index it again
whenever it changes, and prefer the matching Noto CJK face for each language.
---
 .../launcher/runtime/LinuxRuntime.java        | 12 +++++++++++
 tools/linuxfs/desktop/droiddeck-desktop       |  2 +-
 .../overlay/usr/local/bin/droiddeck-session   | 20 +++++++++++++++++++
 3 files changed, 33 insertions(+), 1 deletion(-)

diff --git a/app/src/main/java/com/droiddeck/launcher/runtime/LinuxRuntime.java b/app/src/main/java/com/droiddeck/launcher/runtime/LinuxRuntime.java
index 35a73971f..38a33980a 100644
--- a/app/src/main/java/com/droiddeck/launcher/runtime/LinuxRuntime.java
+++ b/app/src/main/java/com/droiddeck/launcher/runtime/LinuxRuntime.java
@@ -42,6 +42,8 @@ public final class LinuxRuntime {
      * session ended at once. A long host path behind it is proot's to shorten.
      */
     public static final String GUEST_RUNTIME_DIR = "/run/droiddeck";
+    private static final String SYSTEM_FONTS = "/system/fonts";
+    private static final String GUEST_SYSTEM_FONTS = "/usr/local/share/fonts/android";
     /** Where every Linux session's debug log lands: public, so a user can just hand the folder over. */
     public static final String DEBUG_LOG_DIR = "DroidDeck";
 
@@ -207,6 +209,7 @@ public final class LinuxRuntime {
         File shm = new File(context.getCacheDir(), "shm");
         shm.mkdirs();
         bind(cmd, shm.getPath() + ":/dev/shm");
+        bindSystemFonts(cmd, root);
 
         // Android denies apps these; glibc, Steam and libcap read them at startup.
         File fakeProc = new File(root, "etc/droiddeck/proc");
@@ -465,6 +468,15 @@ public final class LinuxRuntime {
         return byType;
     }
 
+    private static void bindSystemFonts(List<String> cmd, File root) {
+        File fonts = new File(SYSTEM_FONTS);
+        File target = new File(root, GUEST_SYSTEM_FONTS.substring(1));
+        if (!fonts.isDirectory() || !fonts.canRead() || !new File(root, "usr/local").isDirectory()) return;
+        if (target.isDirectory() || target.mkdirs()) {
+            bind(cmd, SYSTEM_FONTS + ":" + GUEST_SYSTEM_FONTS);
+        }
+    }
+
     private static void bind(List<String> cmd, String spec) {
         cmd.add("-b");
         cmd.add(spec);
diff --git a/tools/linuxfs/desktop/droiddeck-desktop b/tools/linuxfs/desktop/droiddeck-desktop
index b69c2a993..395799784 100644
--- a/tools/linuxfs/desktop/droiddeck-desktop
+++ b/tools/linuxfs/desktop/droiddeck-desktop
@@ -92,7 +92,7 @@ find "$XDG_RUNTIME_DIR" -mindepth 1 -maxdepth 1 ! -name 'wayland-0*' ! -name 'ke
 # fontconfig's rules (sans-serif -> DejaVu Sans and the rest) live as links in /etc/fonts/conf.d,
 # and the rootfs has none: applications then find fonts but no default font. Firefox logs
 # "no fonts" and draws pages without text.
-if [ -d /usr/share/fontconfig/conf.default ] && ! ls /etc/fonts/conf.d/*.conf >/dev/null 2>&1; then
+if [ -d /usr/share/fontconfig/conf.default ] && ! ls /etc/fonts/conf.d/*.conf 2>/dev/null | grep -qv droiddeck; then
   for f in /usr/share/fontconfig/conf.default/*.conf; do ln -sf "$f" /etc/fonts/conf.d/; done
   echo "== fontconfig: linked $(ls /etc/fonts/conf.d/*.conf | wc -l) default rules"
 fi
diff --git a/tools/linuxfs/overlay/usr/local/bin/droiddeck-session b/tools/linuxfs/overlay/usr/local/bin/droiddeck-session
index 09b769b3b..5bdabd997 100755
--- a/tools/linuxfs/overlay/usr/local/bin/droiddeck-session
+++ b/tools/linuxfs/overlay/usr/local/bin/droiddeck-session
@@ -136,6 +136,26 @@ program_cores() {
 }
 
 if [ -z "${BL_INSIDE:-}" ]; then
+  device_fonts=/usr/local/share/fonts/android
+  if [ -d "$device_fonts" ] && [ -d /etc/fonts/conf.d ] && command -v fc-cache >/dev/null 2>&1; then
+    fonts_rules=$(
+      echo '<?xml version="1.0"?><!DOCTYPE fontconfig SYSTEM "urn:fontconfig:fonts.dtd"><fontconfig>'
+      for pair in "zh-cn=Noto Sans CJK SC" "zh-sg=Noto Sans CJK SC" "zh-tw=Noto Sans CJK TC" "zh-hk=Noto Sans CJK HK" \
+        "zh-mo=Noto Sans CJK HK" "ja=Noto Sans CJK JP" "ko=Noto Sans CJK KR" "th=Noto Sans Thai"; do
+        printf '<match target="pattern"><test name="lang" compare="contains"><string>%s</string></test><edit name="family" mode="prepend_first"><string>%s</string></edit></match>\n' \
+          "${pair%%=*}" "${pair#*=}"
+      done
+      echo '</fontconfig>'
+    )
+    fonts_conf=/etc/fonts/conf.d/66-droiddeck-device-fonts.conf
+    [ "$fonts_rules" = "$(cat "$fonts_conf" 2>/dev/null)" ] || printf '%s\n' "$fonts_rules" > "$fonts_conf"
+    fonts_seen=$(ls -lL "$device_fonts" 2>/dev/null | md5sum)
+    fonts_stamp=/var/cache/fontconfig/.droiddeck-android-fonts
+    if [ "$fonts_seen" != "$(cat "$fonts_stamp" 2>/dev/null)" ]; then
+      fc-cache -f "${device_fonts%/*}" >/dev/null 2>&1 && printf '%s\n' "$fonts_seen" > "$fonts_stamp"
+      echo "== fontconfig: indexed $(ls "$device_fonts" | wc -l) device fonts, zh falls back to $(fc-match -f '%{family[0]}' ':lang=zh-cn' 2>/dev/null)"
+    fi
+  fi
   # The compositor may still be starting, and a socket left by an earlier session is not
   # a compositor: probe until a connection succeeds.
   for _ in $(seq 1 100); do