Use requestUpdate instead of timer in a few GL examples

Change-Id: I235ad367fe693c86ef5a0844fde0573371b284db
Reviewed-by: Laszlo Agocs <laszlo.agocs@qt.io>

examples/opengl/contextinfo/renderwindow.cpp

@@ -181,6 +181,13 @@ void RenderWindow::setupVertexAttribs()
     m_vbo.release();
 }
 
+bool RenderWindow::event(QEvent *ev)
+{
+    if (ev->type() == QEvent::UpdateRequest)
+        render();
+    return QWindow::event(ev);
+}
+
 void RenderWindow::render()
 {
     if (!m_context->makeCurrent(this)) {
@@ -227,9 +234,5 @@ void RenderWindow::render()
 
     m_angle += 1.0f;
 
-    // Instead of 0 wait a few more milliseconds before rendering again. This is
-    // only here to make the UI widgets more responsive on slower machines. We
-    // can afford it since our rendering is so lightweight.
-    const int interval = 5;
-    QTimer::singleShot(interval, this, &RenderWindow::render);
+    requestUpdate();
 }

examples/opengl/contextinfo/renderwindow.h

@@ -72,6 +72,9 @@ signals:
     void ready();
     void error(const QString &msg);
 
+protected:
+    bool event(QEvent *ev) override;
+
 private slots:
     void render();
 

examples/opengl/hellowindow/hellowindow.cpp

@@ -98,6 +98,15 @@ void HelloWindow::exposeEvent(QExposeEvent *)
         m_renderer->render();
 }
 
+bool HelloWindow::event(QEvent *ev)
+{
+    if (ev->type() == QEvent::UpdateRequest) {
+        m_renderer->render();
+        requestUpdate();
+    }
+    return QWindow::event(ev);
+}
+
 void HelloWindow::mousePressEvent(QMouseEvent *)
 {
     updateColor();
@@ -132,7 +141,7 @@ void Renderer::setAnimating(HelloWindow *window, bool animating)
     if (animating) {
         m_windows << window;
         if (m_windows.size() == 1)
-            QTimer::singleShot(0, this, &Renderer::render);
+            window->requestUpdate();
     } else {
         m_currentWindow = 0;
         m_windows.removeOne(window);
@@ -196,8 +205,6 @@ void Renderer::render()
     m_context->swapBuffers(surface);
 
     m_fAngle += 1.0f;
-
-    QTimer::singleShot(0, this, &Renderer::render);
 }
 
 Q_GLOBAL_STATIC(QMutex, initMutex)

examples/opengl/hellowindow/hellowindow.h

@@ -112,11 +112,12 @@ public:
     QColor color() const;
     void updateColor();
 
+protected:
+    bool event(QEvent *ev) override;
     void exposeEvent(QExposeEvent *event) override;
-
-private:
     void mousePressEvent(QMouseEvent *) override;
 
+private:
     int m_colorIndex;
     QColor m_color;
     const QSharedPointer<Renderer> m_renderer;