option to disable qt's hidpi scaling

https://anki.tenderapp.com/discussions/beta-testing/765-problem-with-the-ui-of-anki

aqt/__init__.py

@@ -223,6 +223,8 @@ def parseArgs(argv):
     parser.add_option("-b", "--base", help="path to base folder")
     parser.add_option("-p", "--profile", help="profile name to load")
     parser.add_option("-l", "--lang", help="interface language (en, de, etc)")
+    parser.add_option("--lodpi", action="store_true", dest="lodpi",
+                      help="disable Qt's high DPI support")
     return parser.parse_args(argv[1:])
 
 def run():
@@ -259,7 +261,8 @@ def _run(argv=None, exec=True):
         ctypes.CDLL('libGL.so.1', ctypes.RTLD_GLOBAL)
 
     # opt in to full hidpi support
-    QCoreApplication.setAttribute(Qt.AA_EnableHighDpiScaling)
+    if not opts.lodpi:
+        QCoreApplication.setAttribute(Qt.AA_EnableHighDpiScaling)
 
     # create the app
     app = AnkiApp(argv)

aqt/webview.py

@@ -6,7 +6,7 @@ import sys
 import math
 from anki.hooks import runHook
 from aqt.qt import *
-from aqt.utils import openLink
+from aqt.utils import openLink, showWarning
 from anki.utils import isMac, isWin, isLin, devMode
 
 # Page for debug messages
@@ -73,6 +73,8 @@ class AnkiWebPage(QWebEnginePage):
 # Main web view
 ##########################################################################
 
+dpiWarned = False
+
 class AnkiWebView(QWebEngineView):
 
     def __init__(self, parent=None):
@@ -157,6 +159,7 @@ class AnkiWebView(QWebEngineView):
             oldFocus.setFocus()
 
     def zoomFactor(self):
+        global dpiWarned
         if isMac:
             return 1
         screen = QApplication.desktop().screen()
@@ -167,6 +170,9 @@ class AnkiWebView(QWebEngineView):
             return factor
         # compensate for qt's integer scaling
         # on windows
+        if isWin and screen.physicalDpiX() % 72 != 0 and not dpiWarned:
+            showWarning("Unexpected physical DPI - try starting Anki with --lodpi")
+            dpiWarned = True
         qtIntScale = 72/screen.physicalDpiX()
         desiredScale = factor * qtIntScale
         newFactor = desiredScale / qtIntScale