Windows QPA: Add detection of dark mode

Read the dark mode setting and make it accessible
via native interface.
Add a command line option to set the support level.

Task-number: QTBUG-72028
Change-Id: I1e9fe296a6b1bda81512d003183038b866b67545
Reviewed-by: Oliver Wolff <oliver.wolff@qt.io>

1 files changed, 15 insertions, 0 deletions

diff --git a/src/gui/kernel/qguiapplication.cpp b/src/gui/kernel/qguiapplication.cpp
index 445ad6b835..1190bd1936 100644
--- a/src/gui/kernel/qguiapplication.cpp
+++ b/src/gui/kernel/qguiapplication.cpp
@@ -592,6 +592,21 @@ static QWindowGeometrySpecification windowGeometrySpecification = Q_WINDOW_GEOME
     \list
         \li \c {altgr}, detect the key \c {AltGr} found on some keyboards as
                Qt::GroupSwitchModifier (since Qt 5.12).
+        \li \c {darkmode=[1|2]} controls how Qt responds to the activation
+               of the \e{Dark Mode for applications} introduced in Windows 10
+               1903 (since Qt 5.15).
+
+               A value of 1 causes Qt to switch the window borders to black
+               when \e{Dark Mode for applications} is activated and no High
+               Contrast Theme is in use. This is intended for applications
+               that implement their own theming.
+
+               A value of 2 will in addition cause the Windows Vista style to
+               be deactivated and switch to the Windows style using a
+               simplified palette in dark mode. This is currently
+               experimental pending the introduction of new style that
+               properly adapts to dark mode.
+
         \li \c {dialogs=[xp|none]}, \c xp uses XP-style native dialogs and
             \c none disables them.