Merge pull request matplotlib#19334 from ericpre/fix_mac_big_sur_qt

FIX: qt backend on mac big sur by setting ENVS

Author: tacaswell

lib/matplotlib/backends/qt_compat.py

@@ -15,6 +15,7 @@
 
 from distutils.version import LooseVersion
 import os
+import platform
 import sys
 
 import matplotlib as mpl
@@ -180,6 +181,15 @@ def is_pyqt5():
     raise AssertionError("Unexpected QT_API: {}".format(QT_API))
 
 
+# Fixes issues with Big Sur
+# https://bugreports.qt.io/browse/QTBUG-87014, fixed in qt 5.15.2
+if (sys.platform == 'darwin' and
+        LooseVersion(platform.mac_ver()[0]) >= LooseVersion("10.16") and
+        LooseVersion(QtCore.qVersion()) < LooseVersion("5.15.2") and
+        "QT_MAC_WANTS_LAYER" not in os.environ):
+    os.environ["QT_MAC_WANTS_LAYER"] = "1"
+
+
 # These globals are only defined for backcompatibility purposes.
 ETS = dict(pyqt=(QT_API_PYQTv2, 4), pyside=(QT_API_PYSIDE, 4),
            pyqt5=(QT_API_PYQT5, 5), pyside2=(QT_API_PYSIDE2, 5))