title: paint() vs paintEvent() in Qt
body: <p>I have two questions.</p>
  
  <ol>
  <li><p>What is the difference between <code>paint()</code> of <code>QGraphicsItem</code> and <code>paintEvent()</code> of <code>QWidget</code> APIs? </p></li>
  <li><p>I am developing a timer kinda GUI, so I am updating the screen every 100ms with <code>paint()</code> API on embedded linux board. It consumes almost all of the CPU. Any idea how to prevent this? </p></li>
  </ol>
  
  <p>Or is there any other method to do this simple graphics?</p>
  
  <ol start="3">
  <li>Also I have multiple <code>QGraphicsScene</code> each with its own <code>QGraphicsView</code> in a grid layout. How to update the individual view from the MainWindow.</li>
  </ol>
  
  <p>Below is the code how I currently do this:</p>
  
  <pre><code>/****SCENE 1*****/
      scene_1 = new QGraphicsScene();
      scene_1-&gt;setBackgroundBrush(Qt::black);
      ui-&gt;gv_1-&gt;setScene(scene_1);
      ui-&gt;gv_1-&gt;setRenderHint(QPainter::Antialiasing);
      circle = scene_1-&gt;addEllipse(50, 80, 150, 150, outlinePen, darkGreyBrush);
      textSlotNo = scene_1-&gt;addText("1", QFont("Arial", 30) );
      textSlotNo-&gt;setDefaultTextColor(Qt::gray);
      textSlotNo-&gt;setPos(0,50);
  
      MyItem *item_1 = new MyItem(1);
      scene_1-&gt;addItem(item_1);
      item_1-&gt;timer = new QTimer();
      connect(item_1-&gt;timer, SIGNAL(timeout()),scene_1, SLOT(update()));
      item_1-&gt;timer-&gt;start(100);
  
  /****SCENE 2*****/
  ......
  </code></pre>
  
  <p><strong>Hardware: TI-AM3354</strong></p>