title: Qt - Draw on canvas
body: <p>I am trying to write a program using <code>Qt5</code> that allows users to draw on canvas like paint. 
  I know that the program has to handle events such as <code>mousePressEvent()</code>, <code>mouseReleaseEvent()</code>, and <code>mouseMoveEvent()</code>. But I am not able to figure out how to use them.</p>
  
  <p>Can you guys give me a simple example on this?</p>