Move setting of AA_EnableHighDpiScaling before creating QApplication.

anntzer · anntzer · commit f00836052b34 · 2019-06-18T14:13:34.000+02:00
This is required by the docs (https://doc.qt.io/qt-5/qt.html#ApplicationAttribute-enum) and Qt 5.12.4 has started emitting a warning otherwise ("Attribute Qt::AA_EnableHighDpiScaling must be set before QCoreApplication is created.")
diff --git a/lib/matplotlib/backends/backend_qt5.py b/lib/matplotlib/backends/backend_qt5.py
@@ -118,6 +118,11 @@ def _create_qApp():
                 if display is None or not re.search(r':\d', display):
                     raise RuntimeError('Invalid DISPLAY variable')
 
+            try:
+                QtWidgets.QApplication.setAttribute(
+                    QtCore.Qt.AA_EnableHighDpiScaling)
+            except AttributeError:  # Attribute only exists for Qt>=5.6.
+                pass
             qApp = QtWidgets.QApplication([b"matplotlib"])
             qApp.lastWindowClosed.connect(qApp.quit)
         else:
@@ -126,7 +131,6 @@ def _create_qApp():
     if is_pyqt5():
         try:
             qApp.setAttribute(QtCore.Qt.AA_UseHighDpiPixmaps)
-            qApp.setAttribute(QtCore.Qt.AA_EnableHighDpiScaling)
         except AttributeError:
             pass
 
