fix missing Qt plugin on macOS

Author: dlech

cv2/__init__.py

@@ -1,8 +1,15 @@
 import importlib
+import os
+import sys
 
 from .cv2 import *
 from .data import *
 
 # wildcard import above does not import "private" variables like __version__
 # this makes them available
 globals().update(importlib.import_module('cv2.cv2').__dict__)
+
+if sys.platform == 'darwin':
+    os.environ['QT_QPA_PLATFORM_PLUGIN_PATH'] = os.path.join(
+        os.path.dirname(os.path.abspath(__file__)), 'qt', 'plugins'
+    )

patches/patchQtPlugins

@@ -0,0 +1,12 @@
+diff --git a/opencv/CMakeLists.txt b/opencv/CMakeLists.txt
+index 8ccad4d03a..0d5e2a79e9 100644
+--- a/opencv/CMakeLists.txt
++++ b/opencv/CMakeLists.txt
+@@ -1164,6 +1164,7 @@ if(WITH_QT OR HAVE_QT)
+   if(HAVE_QT5)
+     status("    QT:" "YES (ver ${Qt5Core_VERSION_STRING})")
+     status("      QT OpenGL support:" HAVE_QT_OPENGL THEN "YES (${Qt5OpenGL_LIBRARIES} ${Qt5OpenGL_VERSION_STRING})" ELSE NO)
++    install(DIRECTORY ${Qt5_DIR}/../../../plugins DESTINATION lib/qt)
+   elseif(HAVE_QT)
+     status("    QT:" "YES (ver ${QT_VERSION_MAJOR}.${QT_VERSION_MINOR}.${QT_VERSION_PATCH} ${QT_EDITION})")
+     status("      QT OpenGL support:" HAVE_QT_OPENGL THEN "YES (${QT_QTOPENGL_LIBRARY})" ELSE NO)

setup.py

@@ -128,6 +128,7 @@ def main():
 
     if sys.platform == 'darwin' and not build_headless:
         cmake_args.append("-DWITH_QT=5")
+        rearrange_cmake_output_data['cv2.qt.plugins.platforms'] = [(r'lib/qt/plugins/platforms/libqcocoa\.dylib')]
 
     if build_headless:
         # it seems that cocoa cannot be disabled so on macOS the package is not truly headless
@@ -144,6 +145,7 @@ def main():
                                                 # https://github.com/skvark/opencv-python/issues/21
         cmake_args.append("-DCMAKE_CXX_FLAGS=-stdlib=libc++")
         cmake_args.append("-DCMAKE_OSX_DEPLOYMENT_TARGET:STRING=10.9")
+        subprocess.check_call("patch -p1 < patches/patchQtPlugins", shell=True)
 
     if sys.platform.startswith('linux'):
         cmake_args.append("-DWITH_IPP=OFF")   # tests fail with IPP compiled with