Linux: Use the system dark mode setting

This comes from the desktop settings portal implemented in KDE 5.24 and
GNOME 42

manual/customize.rst

@@ -49,7 +49,7 @@ Environment variables
       the system theme -- beware of crashes and hangs.
     * ``CALIBRE_SHOW_DEPRECATION_WARNINGS`` - causes calibre to print deprecation warnings to stdout. Useful for calibre developers.
     * ``CALIBRE_NO_DEFAULT_PROGRAMS`` - prevent calibre from automatically registering the filetypes it is capable of handling with Windows.
-    * ``CALIBRE_USE_DARK_PALETTE`` - set it to ``1`` to have calibre use dark colors. Works on **Linux only**.
+    * ``CALIBRE_USE_DARK_PALETTE`` - set it to ``1`` to have calibre use dark colors and ``0`` for light colors. Works on **Linux only**.
     * ``SYSFS_PATH`` - Use if sysfs is mounted somewhere other than /sys
     * ``http_proxy``, ``https_proxy`` - used on Linux to specify an HTTP(S) proxy
 

src/calibre/gui2/__init__.py

@@ -16,7 +16,7 @@ from qt.core import (
     QFileIconProvider, QFileInfo, QFont, QFontDatabase, QFontInfo, QFontMetrics,
     QGuiApplication, QIcon, QIODevice, QLocale, QNetworkProxyFactory, QObject,
     QPalette, QResource, QSettings, QSocketNotifier, QStringListModel, QStyle, Qt,
-    QThread, QTimer, QTranslator, QUrl, pyqtSignal
+    QThread, QTimer, QTranslator, QUrl, pyqtSignal, pyqtSlot
 )
 from threading import Lock, RLock
 
@@ -47,6 +47,8 @@ try:
     NO_URL_FORMATTING = QUrl.UrlFormattingOption.None_
 except AttributeError:
     NO_URL_FORMATTING = getattr(QUrl, 'None')
+if islinux:
+    from qt.dbus import QDBusConnection, QDBusMessage, QDBusVariant
 
 
 class IconResourceManager:
@@ -1234,7 +1236,14 @@ class Application(QApplication):
             elif ismacos:
                 use_dark_palette = False
             else:
-                use_dark_palette = os.environ.get('CALIBRE_USE_DARK_PALETTE') == '1'
+                if 'CALIBRE_USE_DARK_PALETTE' in os.environ:
+                    use_dark_palette = os.environ.get('CALIBRE_USE_DARK_PALETTE') == '1'
+                else:
+                    use_dark_palette = linux_is_system_dark_mode_enabled()
+                    bus = QDBusConnection.sessionBus()
+                    bus.connect(
+                        'org.freedesktop.portal.Desktop', '/org/freedesktop/portal/desktop',
+                        'org.freedesktop.portal.Settings', 'SettingChanged', 'ssv', self.linux_desktop_setting_changed)
             if use_dark_palette:
                 self.set_dark_mode_palette()
             elif self.original_palette_modified:
@@ -1247,6 +1256,18 @@ class Application(QApplication):
             self.load_calibre_style()
         self.on_palette_change()
 
+    if islinux:
+        @pyqtSlot(str, str, QDBusVariant)
+        def linux_desktop_setting_changed(self, namespace, key, val):
+            if (namespace, key) == ('org.freedesktop.appearance', 'color-scheme'):
+                use_dark_palette = val.variant() == 1
+                if use_dark_palette != bool(self.is_dark_theme):
+                    if use_dark_palette:
+                        self.set_dark_mode_palette()
+                    else:
+                        self.set_palette(self.original_palette)
+                self.on_palette_change()
+
     def check_for_windows_palette_change(self):
         use_dark_palette = bool(windows_is_system_dark_mode_enabled())
         if bool(self.is_dark_theme) != use_dark_palette:
@@ -1670,6 +1691,18 @@ def windows_is_system_dark_mode_enabled():
     return False
 
 
+def linux_is_system_dark_mode_enabled():
+    bus = QDBusConnection.sessionBus()
+    m = QDBusMessage.createMethodCall(
+        'org.freedesktop.portal.Desktop', '/org/freedesktop/portal/desktop',
+        'org.freedesktop.portal.Settings', 'Read'
+    )
+    m.setArguments(['org.freedesktop.appearance', 'color-scheme'])
+    reply = bus.call(m, timeout=1000)
+    a = reply.arguments()
+    return len(a) and isinstance(a[0], int) and a[0] == 1
+
+
 def make_view_use_window_background(view):
     p = view.palette()
     p.setColor(QPalette.ColorRole.Base, p.color(QPalette.ColorRole.Window))

src/qt/__init__.py

@@ -1,5 +1,5 @@
 # autogenerated by __main__.py do not edit
-top_level_module_names=('QtCore', 'QtGui', 'QtWidgets', 'QtNetwork', 'QtSvg', 'QtPrintSupport', 'QtWebEngineCore', 'QtWebEngineWidgets')
+top_level_module_names=('QtCore', 'QtGui', 'QtWidgets', 'QtNetwork', 'QtSvg', 'QtPrintSupport', 'QtWebEngineCore', 'QtWebEngineWidgets', 'QtDBus')
 
 
 def __getattr__(name):

src/qt/__main__.py

@@ -22,6 +22,9 @@ module_lists = {
         'QtWebEngineCore',
         'QtWebEngineWidgets',
     ),
+    'dbus': (
+        'QtDBus',
+    )
 }
 
 
@@ -54,7 +57,7 @@ def scan(name):
 
 
 top_level_module_names = ()
-for name in ('core', 'webengine'):
+for name in ('core', 'webengine', 'dbus'):
     top_level_module_names += module_lists[name]
     scan(name)
 with open(f'{base}/__init__.py', 'w') as f:

src/qt/dbus.py

@@ -0,0 +1,14 @@
+#!/usr/bin/env python
+# vim:fileencoding=utf-8
+# License: GPL v3 Copyright: 2021, Kovid Goyal <kovid at kovidgoyal.net>
+
+
+from .loader import dynamic_load
+from .dbus_name_map import name_map, module_names
+
+already_imported = {}
+qt_modules = {}
+
+
+def __getattr__(name):
+    return dynamic_load(name, name_map, already_imported, qt_modules, module_names)

src/qt/dbus.pyi

@@ -0,0 +1,20 @@
+# autogenerated by __main__.py do not edit
+import PyQt6.QtDBus
+QDBus = PyQt6.QtDBus.QDBus
+QDBusAbstractAdaptor = PyQt6.QtDBus.QDBusAbstractAdaptor
+QDBusAbstractInterface = PyQt6.QtDBus.QDBusAbstractInterface
+QDBusArgument = PyQt6.QtDBus.QDBusArgument
+QDBusConnection = PyQt6.QtDBus.QDBusConnection
+QDBusConnectionInterface = PyQt6.QtDBus.QDBusConnectionInterface
+QDBusError = PyQt6.QtDBus.QDBusError
+QDBusInterface = PyQt6.QtDBus.QDBusInterface
+QDBusMessage = PyQt6.QtDBus.QDBusMessage
+QDBusObjectPath = PyQt6.QtDBus.QDBusObjectPath
+QDBusPendingCall = PyQt6.QtDBus.QDBusPendingCall
+QDBusPendingCallWatcher = PyQt6.QtDBus.QDBusPendingCallWatcher
+QDBusPendingReply = PyQt6.QtDBus.QDBusPendingReply
+QDBusReply = PyQt6.QtDBus.QDBusReply
+QDBusServiceWatcher = PyQt6.QtDBus.QDBusServiceWatcher
+QDBusSignature = PyQt6.QtDBus.QDBusSignature
+QDBusUnixFileDescriptor = PyQt6.QtDBus.QDBusUnixFileDescriptor
+QDBusVariant = PyQt6.QtDBus.QDBusVariant

src/qt/dbus_name_map.py

@@ -0,0 +1,22 @@
+# autogenerated by __main__.py do not edit
+name_map = {'QDBus': 'PyQt6.QtDBus',
+ 'QDBusAbstractAdaptor': 'PyQt6.QtDBus',
+ 'QDBusAbstractInterface': 'PyQt6.QtDBus',
+ 'QDBusArgument': 'PyQt6.QtDBus',
+ 'QDBusConnection': 'PyQt6.QtDBus',
+ 'QDBusConnectionInterface': 'PyQt6.QtDBus',
+ 'QDBusError': 'PyQt6.QtDBus',
+ 'QDBusInterface': 'PyQt6.QtDBus',
+ 'QDBusMessage': 'PyQt6.QtDBus',
+ 'QDBusObjectPath': 'PyQt6.QtDBus',
+ 'QDBusPendingCall': 'PyQt6.QtDBus',
+ 'QDBusPendingCallWatcher': 'PyQt6.QtDBus',
+ 'QDBusPendingReply': 'PyQt6.QtDBus',
+ 'QDBusReply': 'PyQt6.QtDBus',
+ 'QDBusServiceWatcher': 'PyQt6.QtDBus',
+ 'QDBusSignature': 'PyQt6.QtDBus',
+ 'QDBusUnixFileDescriptor': 'PyQt6.QtDBus',
+ 'QDBusVariant': 'PyQt6.QtDBus',
+ 'QtDBus': 'PyQt6.QtDBus'}
+module_names = frozenset(('QtDBus',)
+)