Modernize rasterwindow/openglwindow examples to use requestUpdate()

Change-Id: Ib8d0c42db7343247d0431ea008eb17da9ee98f4d
Reviewed-by: Laszlo Agocs <laszlo.agocs@qt.io>

examples/gui/doc/src/openglwindow.qdoc

@@ -34,6 +34,9 @@
 
     \image openglwindow-example.png Screenshot of the OpenGLWindow example
 
+    \note This is a low level example of how to use QWindow with OpenGL.
+    In practice you should consider using the higher level QOpenGLWindow class.
+
     \section1 OpenGLWindow Super Class
 
     Our OpenGLWindow class acts as an API which is then subclassed to do the
@@ -70,9 +73,8 @@
 
     \snippet openglwindow/openglwindow.cpp 2
 
-    The renderLater() function simply puts an update request event on
-    the event loop, which leads to renderNow() being called once the event
-    gets processed.
+    The renderLater() function simply calls QWindow::requestUpdate() to schedule
+    an update for when the system is ready to repaint.
 
     We also call renderNow() when we get an expose event. The exposeEvent() is
     the notification to the window that its exposure, meaning visibility, on
@@ -109,11 +111,11 @@
     \l {http://www.khronos.org/registry/gles/}{Khronos OpenGL ES API Registry}.
 
     If animation has been enabled with OpenGLWindow::setAnimating(true), we
-    call renderLater() to put another update request on the event loop.
+    call renderLater() to schedule another update request.
 
     \snippet openglwindow/openglwindow.cpp 4
 
-    Enabling animation also triggers an update request as shown in the
+    Enabling animation also schedules an update request as shown in the
     following code snippet.
 
     \snippet openglwindow/openglwindow.cpp 5

examples/gui/doc/src/rasterwindow.qdoc

@@ -143,19 +143,16 @@
     \snippet rasterwindow/rasterwindow.cpp 6
 
     We went through a few places where the window needed to repainted
-    immediately. There are some cases where this is not desierable,
+    immediately. There are some cases where this is not desirable,
     but rather let the application return to the event loop and
-    later. We acheive this by posting an even to ourself which will
-    then be delivered when the application returns to the \l
-    QGuiApplication event loop. To avoid posting new requests when one
-    is already pending, we store this state in the \c m_update_pending
-    variable.
+    schedule the repaint for later. We achieve this by requesting
+    an update, using QWindow::requestUpdate(), which will then be
+    delivered when the system is ready to repaint.
 
     \snippet rasterwindow/rasterwindow.cpp 7
 
     We reimplement the virtual \l QObject::event() function to handle
-    the update event we posted to ourselves. When the event comes in
-    we reset the pending update flag and call renderNow() to render
-    the window right away.
+    the update event. When the event comes in we call renderNow() to
+    render the window right away.
 
   */

examples/gui/openglwindow/openglwindow.cpp

@@ -59,7 +59,6 @@
 //! [1]
 OpenGLWindow::OpenGLWindow(QWindow *parent)
     : QWindow(parent)
-    , m_update_pending(false)
     , m_animating(false)
     , m_context(0)
     , m_device(0)
@@ -99,17 +98,13 @@ void OpenGLWindow::render()
 //! [3]
 void OpenGLWindow::renderLater()
 {
-    if (!m_update_pending) {
-        m_update_pending = true;
-        QCoreApplication::postEvent(this, new QEvent(QEvent::UpdateRequest));
-    }
+    requestUpdate();
 }
 
 bool OpenGLWindow::event(QEvent *event)
 {
     switch (event->type()) {
     case QEvent::UpdateRequest:
-        m_update_pending = false;
         renderNow();
         return true;
     default:

examples/gui/openglwindow/openglwindow.h

@@ -82,7 +82,6 @@ protected:
     void exposeEvent(QExposeEvent *event) override;
 
 private:
-    bool m_update_pending;
     bool m_animating;
 
     QOpenGLContext *m_context;

examples/gui/rasterwindow/rasterwindow.cpp

@@ -53,7 +53,6 @@
 //! [1]
 RasterWindow::RasterWindow(QWindow *parent)
     : QWindow(parent)
-    , m_update_pending(false)
 {
     create();
     m_backingStore = new QBackingStore(this);
@@ -68,7 +67,6 @@ RasterWindow::RasterWindow(QWindow *parent)
 bool RasterWindow::event(QEvent *event)
 {
     if (event->type() == QEvent::UpdateRequest) {
-        m_update_pending = false;
         renderNow();
         return true;
     }
@@ -79,10 +77,7 @@ bool RasterWindow::event(QEvent *event)
 //! [6]
 void RasterWindow::renderLater()
 {
-    if (!m_update_pending) {
-        m_update_pending = true;
-        QCoreApplication::postEvent(this, new QEvent(QEvent::UpdateRequest));
-    }
+    requestUpdate();
 }
 //! [6]
 
@@ -99,10 +94,9 @@ void RasterWindow::resizeEvent(QResizeEvent *resizeEvent)
 //! [2]
 void RasterWindow::exposeEvent(QExposeEvent *)
 {
-    if (isExposed()) {
+    if (isExposed())
         renderNow();
 }
-}
 //! [2]
 
 

examples/gui/rasterwindow/rasterwindow.h

@@ -74,7 +74,6 @@ protected:
 
 private:
     QBackingStore *m_backingStore;
-    bool m_update_pending;
 };
 //! [1]
 #endif // RASTERWINDOW_H

src/gui/kernel/qwindow.cpp

@@ -2175,11 +2175,14 @@ void QWindowPrivate::deliverUpdateRequest()
     Schedules a QEvent::UpdateRequest event to be delivered to this window.
 
     The event is delivered in sync with the display vsync on platforms
-    where this is possible. When driving animations, this function should
-    be called once after drawing has completed.
+    where this is possible. Otherwise, the event is delivered after a
+    delay of 5 ms. The additional time is there to give the event loop
+    a bit of idle time to gather system events, and can be overridden
+    using the QT_QPA_UPDATE_IDLE_TIME environment variable.
 
-    Calling this function multiple times will result in a single event
-    being delivered to the window.
+    When driving animations, this function should be called once after drawing
+    has completed. Calling this function multiple times will result in a single
+    event being delivered to the window.
 
     Subclasses of QWindow should reimplement event(), intercept the event and
     call the application's rendering code, then call the base class