Cache font-ids that were already loaded

`get_font_id` also saves the trouble of
specifying the entire path of the fonts.

electrum/gui/common_qt/util.py

@@ -1,13 +1,27 @@
 from typing import Optional
+import os.path
 
 from PyQt6 import QtGui
 from PyQt6.QtCore import Qt
-from PyQt6.QtGui import QColor, QPen, QPaintDevice
+from PyQt6.QtGui import QColor, QPen, QPaintDevice, QFontDatabase
 import qrcode
 
 from electrum.i18n import _
 
 
+_cached_font_ids: dict[str, int] = {}
+
+def get_font_id(filename: str) -> int:
+    font_id = _cached_font_ids.get(filename)
+    if font_id is not None:
+        return font_id
+    # font_id will be negative on error
+    font_id = QFontDatabase.addApplicationFont(
+        os.path.join(os.path.dirname(__file__), '..', 'fonts', filename)
+    )
+    _cached_font_ids[filename] = font_id
+    return font_id
+
 def draw_qr(
     *,
     qr: Optional[qrcode.main.QRCode],

electrum/gui/qml/qeapp.py

@@ -9,7 +9,7 @@ from typing import TYPE_CHECKING, Set
 
 from PyQt6.QtCore import (pyqtSlot, pyqtSignal, pyqtProperty, QObject, QT_VERSION_STR, PYQT_VERSION_STR,
                           qInstallMessageHandler, QTimer, QSortFilterProxyModel)
-from PyQt6.QtGui import QGuiApplication, QFontDatabase
+from PyQt6.QtGui import QGuiApplication
 from PyQt6.QtQml import qmlRegisterType, QQmlApplicationEngine
 
 import electrum
@@ -20,6 +20,7 @@ from electrum.bip21 import BITCOIN_BIP21_URI_SCHEME, LIGHTNING_URI_SCHEME
 from electrum.base_crash_reporter import BaseCrashReporter, EarlyExceptionsQueue
 from electrum.network import Network
 from electrum.plugin import run_hook
+from electrum.gui.common_qt.util import get_font_id
 
 from .qeconfig import QEConfig
 from .qedaemon import QEDaemon
@@ -426,8 +427,8 @@ class ElectrumQmlApplication(QGuiApplication):
 
         # add a monospace font as we can't rely on device having one
         self.fixedFont = 'PT Mono'
-        not_loaded = QFontDatabase.addApplicationFont('electrum/gui/fonts/PTMono-Regular.ttf') < 0
-        not_loaded = QFontDatabase.addApplicationFont('electrum/gui/fonts/PTMono-Bold.ttf') < 0 and not_loaded
+        not_loaded = get_font_id('PTMono-Regular.ttf') < 0
+        not_loaded = get_font_id('PTMono-Bold.ttf') < 0 and not_loaded
         if not_loaded:
             self.logger.warning('Could not load font PT Mono')
             self.fixedFont = 'Monospace' # hope for the best