Allow platform to decide default behavior for show() based on window flags

The ShowIsMaximized and ShowIsFullscreen style hints were not granular
enough to build a default behavior from that would be correct for all
platforms. The recent Android patch that excluded dialogs from being
shown maximized (Ia249e93dbbea1) has now been moved into a platform
override in the Android integration plugin, leaving other platforms
to the default behavior of using the style-hints. We still special
case popup-windows though, as that behavior has been there for a
while.

Task-number: QTBUG-34969
Change-Id: Id36346d71bfc46171383ffe334592ca0b94e456f
Reviewed-by: BogDan Vatra <bogdan@kde.org>
Reviewed-by: Paul Olav Tvete <paul.tvete@digia.com>

src/gui/kernel/qplatformintegration.cpp

@@ -364,6 +364,20 @@ QVariant QPlatformIntegration::styleHint(StyleHint hint) const
     return 0;
 }
 
+Qt::WindowState QPlatformIntegration::defaultWindowState(Qt::WindowFlags flags) const
+{
+    // Leave popup-windows as is
+    if (flags & Qt::Popup & ~Qt::Window)
+        return Qt::WindowNoState;
+
+    if (styleHint(QPlatformIntegration::ShowIsFullScreen).toBool())
+        return Qt::WindowFullScreen;
+    else if (styleHint(QPlatformIntegration::ShowIsMaximized).toBool())
+        return Qt::WindowMaximized;
+
+    return Qt::WindowNoState;
+}
+
 Qt::KeyboardModifiers QPlatformIntegration::queryKeyboardModifiers() const
 {
     return QGuiApplication::keyboardModifiers();

src/gui/kernel/qplatformintegration.h

@@ -152,6 +152,7 @@ public:
     };
 
     virtual QVariant styleHint(StyleHint hint) const;
+    virtual Qt::WindowState defaultWindowState(Qt::WindowFlags) const;
 
     virtual Qt::KeyboardModifiers queryKeyboardModifiers() const;
     virtual QList<int> possibleKeys(const QKeyEvent *) const;

src/gui/kernel/qstylehints.cpp

@@ -176,6 +176,9 @@ int QStyleHints::cursorFlashTime() const
     Returns \c true if the platform defaults to windows being fullscreen,
     otherwise \c false.
 
+    \note The platform may still choose to show certain windows non-fullscreen,
+    such as popups or dialogs. This method only returns the default behavior.
+
     \sa QWindow::show()
 */
 bool QStyleHints::showIsFullScreen() const

src/gui/kernel/qwindow.cpp

@@ -1651,18 +1651,17 @@ QObject *QWindow::focusObject() const
 /*!
     Shows the window.
 
-    This equivalent to calling showFullScreen() or showNormal(), depending
-    on whether the platform defaults to windows being fullscreen or not, and
-    whether the window is a popup.
+    This is equivalent to calling showFullScreen(), showMaximized(), or showNormal(),
+    depending on the platform's default behavior for the window type and flags.
 
-    \sa showFullScreen(), showNormal(), hide(), QStyleHints::showIsFullScreen(), flags()
+    \sa showFullScreen(), showMaximized(), showNormal(), hide(), QStyleHints::showIsFullScreen(), flags()
 */
 void QWindow::show()
 {
-    bool isPopup = d_func()->windowFlags & Qt::Popup & ~Qt::Window;
-    if (!isPopup && qApp->styleHints()->showIsFullScreen())
+    Qt::WindowState defaultState = QGuiApplicationPrivate::platformIntegration()->defaultWindowState(d_func()->windowFlags);
+    if (defaultState == Qt::WindowFullScreen)
         showFullScreen();
-    else if (!isPopup && !(d_func()->windowFlags & Qt::Dialog & ~Qt::Window) && QGuiApplicationPrivate::platformIntegration()->styleHint(QPlatformIntegration::ShowIsMaximized).toBool())
+    else if (defaultState == Qt::WindowMaximized)
         showMaximized();
     else
         showNormal();

src/plugins/platforms/android/src/qandroidplatformintegration.cpp

@@ -242,6 +242,15 @@ QVariant QAndroidPlatformIntegration::styleHint(StyleHint hint) const
     }
 }
 
+Qt::WindowState QAndroidPlatformIntegration::defaultWindowState(Qt::WindowFlags flags) const
+{
+    // Don't maximize dialogs on Android
+    if (flags & Qt::Dialog & ~Qt::Window)
+        return Qt::WindowNoState;
+
+    return QPlatformIntegration::defaultWindowState(flags);
+}
+
 static const QLatin1String androidThemeName("android");
 QStringList QAndroidPlatformIntegration::themeNames() const
 {

src/plugins/platforms/android/src/qandroidplatformintegration.h

@@ -121,6 +121,7 @@ public:
 #endif
 
     QVariant styleHint(StyleHint hint) const;
+    Qt::WindowState defaultWindowState(Qt::WindowFlags flags) const Q_DECL_OVERRIDE;
 
     QStringList themeNames() const;
     QPlatformTheme *createPlatformTheme(const QString &name) const;

src/widgets/kernel/qwidget.cpp

@@ -6999,23 +6999,23 @@ void QWidget::setUpdatesEnabled(bool enable)
 }
 
 /*!
-    Shows the widget and its child widgets. This function is
-    equivalent to setVisible(true) in the normal case, and equivalent
-    to showFullScreen() if the QStyleHints::showIsFullScreen() hint
-    is true and the window is not a popup.
+    Shows the widget and its child widgets.
 
-    \sa raise(), showEvent(), hide(), setVisible(), showMinimized(), showMaximized(),
-    showNormal(), isVisible(), windowFlags()
+    This is equivalent to calling showFullScreen(), showMaximized(), or setVisible(true),
+    depending on the platform's default behavior for the window flags.
+
+     \sa raise(), showEvent(), hide(), setVisible(), showMinimized(), showMaximized(),
+    showNormal(), isVisible(), windowFlags(), flags()
 */
 void QWidget::show()
 {
-    bool isPopup = data->window_flags & Qt::Popup & ~Qt::Window;
-    if (isWindow() && !isPopup && qApp->styleHints()->showIsFullScreen())
+    Qt::WindowState defaultState = QGuiApplicationPrivate::platformIntegration()->defaultWindowState(data->window_flags);
+    if (defaultState == Qt::WindowFullScreen)
         showFullScreen();
-    else if (isWindow() && !(data->window_flags & Qt::Dialog & ~Qt::Window) && !isPopup && QGuiApplicationPrivate::platformIntegration()->styleHint(QPlatformIntegration::ShowIsMaximized).toBool())
+    else if (defaultState == Qt::WindowMaximized)
         showMaximized();
     else
-        setVisible(true);
+        setVisible(true); // FIXME: Why not showNormal(), like QWindow::show()?
 }
 
 /*! \internal