Display monitor hotplugging v2

application.nix

@@ -21,7 +21,19 @@ rec {
       (import ./application/overlays version)
     ];
 
-    module = { config, lib, pkgs, ... }: {
+    module = { config, lib, pkgs, ... }:
+    let
+      selectDisplay = pkgs.writeShellApplication {
+        name = "select-display";
+        runtimeInputs = with pkgs; [
+          gnugrep
+          gawk
+          xorg.xrandr
+          bash
+        ];
+        text = (builtins.readFile ./application/select-display.sh);
+      };
+    in {
 
       imports = [
         ./application/playos-status.nix
@@ -67,6 +79,9 @@ rec {
               xset s noblank
               xset -dpms
 
+              # Select best display to output to
+              ${selectDisplay}/bin/select-display || true
+
               # Localization for xsession
               if [ -f /var/lib/gui-localization/lang ]; then
                 export LANG=$(cat /var/lib/gui-localization/lang)
@@ -75,19 +90,6 @@ rec {
                 setxkbmap $(cat /var/lib/gui-localization/keymap) || true
               fi
 
-              # Set preferred screen resolution
-              scaling_pref=$(cat /var/lib/gui-localization/screen-scaling 2>/dev/null || echo "default")
-              case "$scaling_pref" in
-                "default" | "full-hd")
-                  xrandr --size 1920x1080;;
-                "native")
-                  # Nothing to do, let system decide.
-                  ;;
-                *)
-                  echo "Unknown scaling preference '$scaling_pref'. Ignoring."
-                  ;;
-              esac
-
               # Enable Qt WebEngine Developer Tools (https://doc.qt.io/qt-6/qtwebengine-debugging.html)
               export QTWEBENGINE_REMOTE_DEBUGGING="127.0.0.1:3355"
 
@@ -145,6 +147,24 @@ rec {
         wantedBy = [ "multi-user.target" ];
       };
 
+      # Monitor hotplugging
+      services.udev.extraRules = ''
+        ACTION=="change", SUBSYSTEM=="drm", RUN+="${pkgs.systemd}/bin/systemctl start select-display.service"
+      '';
+      systemd.services."select-display" = {
+        description = "Select best display to output to";
+        serviceConfig = {
+          Type = "oneshot";
+          ExecStart = "${selectDisplay}/bin/select-display";
+          User = "play";
+        };
+        environment = {
+          XAUTHORITY = "${config.users.users.play.home}/.Xauthority";
+          DISPLAY = ":0";
+        };
+        after = [ "graphical.target" ];
+      };
+
       # Audio
       sound.enable = true;
       hardware.pulseaudio = {

application/select-display.sh

@@ -0,0 +1,48 @@
+set -euo pipefail
+
+SCALING_PREF=$(cat /var/lib/gui-localization/screen-scaling 2>/dev/null || echo "default")
+readonly SCALING_PREF
+
+CONNECTED_OUTPUTS=$(xrandr | grep ' connected' | awk '{ print $1 }')
+readonly CONNECTED_OUTPUTS
+
+echo -e "Connected outputs:\n$CONNECTED_OUTPUTS\n"
+
+scaling_pref_params=""
+
+echo "Using scaling preference '$SCALING_PREF'"
+
+case "$SCALING_PREF" in
+    "default" | "full-hd")
+        scaling_pref_params=(--mode 1920x1080)
+        ;;
+    "native")
+        scaling_pref_params=(--auto)
+        ;;
+    *)
+        scaling_pref_params=(--auto)
+        ;;
+esac
+
+if [ -z "$CONNECTED_OUTPUTS" ]; then
+
+    echo "Error: no connected outputs found. Not applying any changes."
+
+else
+
+    first_functional_output=""
+    for output in $CONNECTED_OUTPUTS; do
+        if [ -z "$first_functional_output" ]; then
+            if xrandr --output "$output" --primary "${scaling_pref_params[@]}"; then
+                first_functional_output=$output
+                echo "Configured display $output as primary"
+            else
+                echo "Failed to configure display $output"
+            fi
+        else
+            xrandr --output "$output" \
+                --same-as "$first_functional_output" \
+                "${scaling_pref_params[@]}" || echo "Failed to configure display $output"
+        fi
+    done
+fi

kiosk/kiosk_browser/__init__.py

@@ -17,21 +17,19 @@ def start(kiosk_url, settings_url, toggle_settings_key, fullscreen = True):
     mainWidget = main_widget.MainWidget(
         kiosk_url = parseUrl(kiosk_url),
         settings_url = parseUrl(settings_url),
-        toggle_settings_key = QKeySequence(toggle_settings_key)
+        toggle_settings_key = QKeySequence(toggle_settings_key),
+        fullscreen = fullscreen
     )
 
     mainWidget.setContextMenuPolicy(Qt.ContextMenuPolicy.NoContextMenu)
 
-    screen_size = app.primaryScreen().size()
-
-    if fullscreen:
-        # Without a Window Manager, showFullScreen does not work under X,
-        # so set the window size to the primary screen size.
-        mainWidget.resize(screen_size)
-        mainWidget.showFullScreen()
-    else:
-        mainWidget.resize(QSize(round(screen_size.width() / 2), round(screen_size.height() / 2)))
-        mainWidget.show()
+    # Note: Qt primary screen != xrandr primary screen
+    # Qt will set primary when screen becomes visible, while on
+    # xrandr it only changes when `--primary` is explicitly specified
+    app.primaryScreenChanged.connect(mainWidget.handle_screen_change,
+        type=Qt.ConnectionType.QueuedConnection)
+    primary = app.primaryScreen()
+    mainWidget.handle_screen_change(primary)
 
     # Quit application gracefully when receiving SIGINT or SIGTERM
     # This is important to trigger flushing of in-memory DOM storage to disk

kiosk/kiosk_browser/main_widget.py

@@ -1,5 +1,6 @@
 from PyQt6 import QtWidgets, QtCore, QtGui
 import time
+import logging
 
 from kiosk_browser import browser_widget, captive_portal, dialogable_widget, proxy as proxy_module
 
@@ -11,8 +12,12 @@ class MainWidget(QtWidgets.QWidget):
     - Use proxy configured in Connman.
     """
 
-    def __init__(self, kiosk_url: str, settings_url: str, toggle_settings_key: str):
+    def __init__(self, kiosk_url: str, settings_url: str,
+                 toggle_settings_key: str, fullscreen: bool):
         super(MainWidget, self).__init__()
+        # Display
+        self._primary_screen_con = None
+        self._fullscreen = fullscreen
 
         # Proxy
         proxy = proxy_module.Proxy()
@@ -102,3 +107,27 @@ def eventFilter(self, source, event):
                 self._menu_press_since = None
 
         return super(MainWidget, self).eventFilter(source, event)
+
+    def handle_screen_change(self, new_primary):
+        logging.info(f"Primary screen changed to {new_primary.name()}")
+        if self._primary_screen_con is not None:
+            QtCore.QObject.disconnect(self._primary_screen_con)
+
+        self._primary_screen_con = \
+            new_primary.geometryChanged.connect(self._resize_to_screen)
+
+        # Precautionary sleep to allow Chromium to update screens
+        time.sleep(1)
+        self._resize_to_screen(new_primary.geometry())
+
+    def _resize_to_screen(self, new_geom):
+        screen_size = new_geom.size()
+        logging.info(f"Resizing widget based on new screen size: {screen_size}")
+        if self._fullscreen:
+            # Without a Window Manager, showFullScreen does not work under X,
+            # so set the window size to the primary screen size.
+            self.resize(screen_size)
+            self.showFullScreen()
+        else:
+            self.resize(QtCore.QSize(round(screen_size.width() / 2), round(screen_size.height() / 2)))
+            self.show()