highgui: win32ui plugin

modules/highgui/cmake/detect_win32ui.cmake

@@ -0,0 +1,17 @@
+#--- Win32 UI ---
+ocv_clear_vars(HAVE_WIN32UI)
+if(WITH_WIN32UI)
+  try_compile(HAVE_WIN32UI
+    "${CMAKE_CURRENT_BINARY_DIR}"
+    "${OpenCV_SOURCE_DIR}/cmake/checks/win32uitest.cpp"
+    CMAKE_FLAGS "-DLINK_LIBRARIES:STRING=user32;gdi32")
+  if(HAVE_WIN32UI)
+    set(__libs "user32" "gdi32")
+    if(OpenCV_ARCH STREQUAL "ARM64")
+      list(APPEND __libs "comdlg32" "advapi32")
+    endif()
+    ocv_add_external_target(win32ui "" "${__libs}" "HAVE_WIN32UI")
+  endif()
+endif()
+
+set(HAVE_WIN32UI "${HAVE_WIN32UI}" PARENT_SCOPE)  # informational

modules/highgui/cmake/init.cmake

@@ -43,8 +43,7 @@ else()
 endif()
 
 add_backend("gtk" WITH_GTK)
-
-# TODO win32
+add_backend("win32ui" WITH_WIN32UI)
 # TODO cocoa
 # TODO qt
 # TODO opengl