Make QWindow's windowState a QFlags of the WindowState

This reflects QWidget API, and restores some behavior from Qt4.
Some WM can have several state at the same time. On Plasma for example,
when a window is both maximized and minimized, the "maximized" checkbox
is checked from the taskbar entry.

The API of QPlatformWindow was changed to take a QFlag and the platform
plugins were adapted.

 - On XCB: Always send the full state to the WM. And read the full state.

 - On Windows: The code was originally written with '&' in Qt4, and was changed
   to == when porting. Some adaptation had to be made so the states would be
   preserved.

 - On macOS: Only a single state can be set and is reported back for now,
   with the possibly to expand this in the future.

 - Other platforms: Just do as before with the effective state.

Task-number: QTBUG-57882
Task-number: QTBUG-52616
Task-number: QTBUG-52555
Change-Id: I7a1f7cac64236bbd4c591f796374315639233dad
Reviewed-by: Gunnar Sletta <gunnar@crimson.no>
Reviewed-by: Robin Burchell <robin.burchell@crimson.no>

1 files changed, 2 insertions, 0 deletions

diff --git a/src/gui/kernel/qwindow.h b/src/gui/kernel/qwindow.h
index 2883749d2e..033678cf5a 100644
--- a/src/gui/kernel/qwindow.h
+++ b/src/gui/kernel/qwindow.h
@@ -189,7 +189,9 @@ public:
     qreal devicePixelRatio() const;
 
     Qt::WindowState windowState() const;
+    Qt::WindowStates windowStates() const;
     void setWindowState(Qt::WindowState state);
+    void setWindowStates(Qt::WindowStates states);
 
     void setTransientParent(QWindow *parent);
     QWindow *transientParent() const;