add minimal theme detection on Linux

Closes #1116

qt/aqt/main.py

@@ -31,7 +31,7 @@ from anki.decks import DeckDict, DeckId
 from anki.hooks import runHook
 from anki.notes import NoteId
 from anki.sound import AVTag, SoundOrVideoTag
-from anki.utils import devMode, ids2str, int_time, isMac, isWin, split_fields
+from anki.utils import devMode, ids2str, int_time, isLin, isMac, isWin, split_fields
 from aqt import gui_hooks
 from aqt.addons import DownloadLogEntry, check_and_prompt_for_updates, show_log_to_user
 from aqt.dbcheck import check_db
@@ -1005,8 +1005,17 @@ title="{}" {}>{}</button>""".format(
 
     def setupStyle(self) -> None:
         theme_manager.apply_style()
+        if isLin:
+            # On Linux, the check requires invoking an external binary,
+            # which we don't want to be doing frequently
+            interval_secs = 300
+        else:
+            interval_secs = 5
         self.progress.timer(
-            5 * 1000, theme_manager.apply_style_if_system_style_changed, True, False
+            interval_secs * 1000,
+            theme_manager.apply_style_if_system_style_changed,
+            True,
+            False,
         )
 
     def set_theme(self, theme: Theme) -> None:

qt/aqt/platform.py

@@ -6,11 +6,12 @@
 from __future__ import annotations
 
 import os
+import subprocess
 import sys
 from ctypes import CDLL
 
 import aqt.utils
-from anki.utils import isMac, isWin
+from anki.utils import isLin, isMac, isWin
 
 
 def get_windows_dark_mode() -> bool:
@@ -56,6 +57,26 @@ def get_macos_dark_mode() -> bool:
         return False
 
 
+def get_linux_dark_mode() -> bool:
+    """True if Linux system is in dark mode.
+    This only works if the GTK theme name contains '-dark'"""
+    if not isLin:
+        return False
+    try:
+        process = subprocess.run(
+            ["gsettings", "get", "org.gnome.desktop.interface", "gtk-theme"],
+            check=True,
+            capture_output=True,
+            encoding="utf8",
+        )
+    except FileNotFoundError as e:
+        # swallow exceptions, as gsettings may not be installed
+        print(e)
+        return False
+
+    return "-dark" in process.stdout.lower()
+
+
 _ankihelper_dll: CDLL | None = None
 
 

qt/aqt/theme.py

@@ -10,7 +10,12 @@ from dataclasses import dataclass
 import aqt
 from anki.utils import isMac
 from aqt import QApplication, colors, gui_hooks, isWin
-from aqt.platform import get_macos_dark_mode, get_windows_dark_mode, set_macos_dark_mode
+from aqt.platform import (
+    get_linux_dark_mode,
+    get_macos_dark_mode,
+    get_windows_dark_mode,
+    set_macos_dark_mode,
+)
 from aqt.qt import (
     QColor,
     QGuiApplication,
@@ -164,8 +169,7 @@ class ThemeManager:
             elif isMac:
                 return get_macos_dark_mode()
             else:
-                # not supported on Linux
-                return False
+                return get_linux_dark_mode()
 
     def apply_style_if_system_style_changed(self) -> None:
         theme = aqt.mw.pm.theme()