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>

2 files changed, 10 insertions, 37 deletions

diff --git a/src/widgets/kernel/qwidget.cpp b/src/widgets/kernel/qwidget.cpp
index 8d5c3e415a..62d723bea5 100644
--- a/src/widgets/kernel/qwidget.cpp
+++ b/src/widgets/kernel/qwidget.cpp
@@ -3037,17 +3037,6 @@ void QWidget::overrideWindowState(Qt::WindowStates newstate)
     QApplication::sendEvent(this, &e);
 }
 
-Qt::WindowState effectiveState(Qt::WindowStates state)
-{
-    if (state & Qt::WindowMinimized)
-        return Qt::WindowMinimized;
-    else if (state & Qt::WindowFullScreen)
-        return Qt::WindowFullScreen;
-    else if (state & Qt::WindowMaximized)
-        return Qt::WindowMaximized;
-    return Qt::WindowNoState;
-}
-
 /*!
     \fn void QWidget::setWindowState(Qt::WindowStates windowState)
 
@@ -3089,19 +3078,17 @@ void QWidget::setWindowState(Qt::WindowStates newstate)
 
     data->window_state = newstate;
     data->in_set_window_state = 1;
-    Qt::WindowState newEffectiveState = effectiveState(newstate);
-    Qt::WindowState oldEffectiveState = effectiveState(oldstate);
-    if (isWindow() && newEffectiveState != oldEffectiveState) {
+    if (isWindow()) {
         // Ensure the initial size is valid, since we store it as normalGeometry below.
         if (!testAttribute(Qt::WA_Resized) && !isVisible())
             adjustSize();
 
         d->createTLExtra();
-        if (oldEffectiveState == Qt::WindowNoState)
+        if (!(oldstate & (Qt::WindowMinimized | Qt::WindowMaximized | Qt::WindowFullScreen)))
             d->topData()->normalGeometry = geometry();
 
         Q_ASSERT(windowHandle());
-        windowHandle()->setWindowState(newEffectiveState);
+        windowHandle()->setWindowStates(newstate & ~Qt::WindowActive);
     }
     data->in_set_window_state = 0;
 
diff --git a/src/widgets/kernel/qwidgetwindow.cpp b/src/widgets/kernel/qwidgetwindow.cpp
index 31f2d672bb..44fd4b6a80 100644
--- a/src/widgets/kernel/qwidgetwindow.cpp
+++ b/src/widgets/kernel/qwidgetwindow.cpp
@@ -726,8 +726,6 @@ void QWidgetWindow::repaintWindow()
                                                  QWidgetBackingStore::UpdateNow, QWidgetBackingStore::BufferInvalid);
 }
 
-Qt::WindowState effectiveState(Qt::WindowStates state);
-
 // Store normal geometry used for saving application settings.
 void QWidgetWindow::updateNormalGeometry()
 {
@@ -738,7 +736,7 @@ void QWidgetWindow::updateNormalGeometry()
     QRect normalGeometry;
     if (const QPlatformWindow *pw = handle())
         normalGeometry = QHighDpi::fromNativePixels(pw->normalGeometry(), this);
-    if (!normalGeometry.isValid() && effectiveState(m_widget->windowState()) == Qt::WindowNoState)
+    if (!normalGeometry.isValid() && !(m_widget->windowState() & ~Qt::WindowActive))
         normalGeometry = m_widget->geometry();
     if (normalGeometry.isValid())
         tle->normalGeometry = normalGeometry;
@@ -930,30 +928,18 @@ void QWidgetWindow::handleWindowStateChangedEvent(QWindowStateChangeEvent *event
     // QWindow does currently not know 'active'.
     Qt::WindowStates eventState = event->oldState();
     Qt::WindowStates widgetState = m_widget->windowState();
+    Qt::WindowStates windowState = windowStates();
     if (widgetState & Qt::WindowActive)
         eventState |= Qt::WindowActive;
 
     // Determine the new widget state, remember maximized/full screen
     // during minimized.
-    switch (windowState()) {
-    case Qt::WindowNoState:
-        widgetState &= ~(Qt::WindowMinimized | Qt::WindowMaximized | Qt::WindowFullScreen);
-        break;
-    case Qt::WindowMinimized:
+    if (windowState & Qt::WindowMinimized) {
         widgetState |= Qt::WindowMinimized;
-        break;
-    case Qt::WindowMaximized:
-        updateNormalGeometry();
-        widgetState |= Qt::WindowMaximized;
-        widgetState &= ~(Qt::WindowMinimized | Qt::WindowFullScreen);
-        break;
-    case Qt::WindowFullScreen:
-        updateNormalGeometry();
-        widgetState |= Qt::WindowFullScreen;
-        widgetState &= ~(Qt::WindowMinimized);
-        break;
-    case Qt::WindowActive: // Not handled by QWindow
-        break;
+    } else {
+        widgetState = windowState | (widgetState & Qt::WindowActive);
+        if (windowState) // Maximized or FullScreen
+            updateNormalGeometry();
     }
 
     // Sent event if the state changed (that is, it is not triggered by