Introduced QWindow::isExposed().

The visible property along with show/hideEvent tracks the
windows visibility from the application perspective and is
really a request. The exposeEvent() along with the isExposed()
accessor is used to notify the application of the actual
state of the window in the windowing system.

Change-Id: I7f5b7ed74a168e34aaa21ce0ae9042ddfb0bf6d8
Reviewed-by: Samuel Rødal <samuel.rodal@nokia.com>

src/gui/kernel/qplatformwindow_qpa.cpp

@@ -142,6 +142,7 @@ QMargins QPlatformWindow::frameMargins() const
 void QPlatformWindow::setVisible(bool visible)
 {
     Q_UNUSED(visible);
+    QWindowSystemInterface::handleSynchronousExposeEvent(window(), QRect(QPoint(), geometry().size()));
 }
 /*!
     Requests setting the window flags of this surface
@@ -152,6 +153,20 @@ Qt::WindowFlags QPlatformWindow::setWindowFlags(Qt::WindowFlags flags)
     return flags;
 }
 
+
+
+/*!
+    Returns if this window is exposed in the windowing system.
+
+    An exposeEvent() is sent every time this value changes.
+ */
+
+bool QPlatformWindow::isExposed() const
+{
+    Q_D(const QPlatformWindow);
+    return d->window->visible();
+}
+
 /*!
     Requests setting the window state of this surface
     to \a type. Returns the actual state set.

src/gui/kernel/qplatformwindow_qpa.h

@@ -89,6 +89,8 @@ public:
     virtual void raise();
     virtual void lower();
 
+    virtual bool isExposed() const;
+
     virtual void propagateSizeHints();
 
     virtual void setOpacity(qreal level);

src/gui/kernel/qwindow.cpp

@@ -374,6 +374,25 @@ void QWindow::requestActivateWindow()
         d->platformWindow->requestActivateWindow();
 }
 
+
+/*!
+    Returns if this window is exposed in the windowing system.
+
+    When the window is not exposed, it is shown by the application
+    but it is still not showing in the windowing system, so the application
+    should minimize rendering and other graphical activities.
+
+    An exposeEvent() is sent every time this value changes.
+ */
+
+bool QWindow::isExposed() const
+{
+    Q_D(const QWindow);
+    if (d->platformWindow)
+        return d->platformWindow->isExposed();
+    return false;
+}
+
 /*!
     Returns true if the window should appear active from a style perspective.
 
@@ -888,6 +907,19 @@ bool QWindow::close()
     return true;
 }
 
+
+
+/*!
+    The expose event is sent by the window system whenever the window's
+    exposure on screen changes.
+
+    If the window is moved off screen, is made totally obscured by another
+    window, iconified or similar, this function might be called and the
+    value of isExposed() might change to false. When this happens,
+    an application should stop its rendering as it is no longer visible
+    to the user.
+ */
+
 void QWindow::exposeEvent(QExposeEvent *ev)
 {
     ev->ignore();

src/gui/kernel/qwindow.h

@@ -152,6 +152,8 @@ public:
 
     bool isAncestorOf(const QWindow *child, AncestorMode mode = IncludeTransients) const;
 
+    bool isExposed() const;
+
     QSize minimumSize() const;
     QSize maximumSize() const;
     QSize baseSize() const;

src/plugins/platforms/windows/qwindowswindow.cpp

@@ -708,6 +708,7 @@ void QWindowsWindow::setVisible(bool visible)
             hide_sys();
         }
     }
+    QWindowSystemInterface::handleSynchronousExposeEvent(window(), QRect(QPoint(), geometry().size()));
 }
 
 bool QWindowsWindow::isVisible() const