title: Zooming in/out on a mouser point ?
body: <p>As seen in the pictures.
  <img src="https://i.stack.imgur.com/tABMP.png" alt="alt text"></p>
  
  <p><img src="https://i.stack.imgur.com/epcYK.png" alt="alt text"></p>
  
  <p>I have QWidget inside a QScrollArea.
  QWidget act as a render widget for cell image  and some vector based contour data.
  User can performe zoom in/out  and what simply happens is, it changes the QPainters scale and change the size of QWidget size accordinly.</p>
  
  <p>Now I want to perform the zooming in/out on the  point under the mouse. (like zooming action  in GIMP).
  How to calculate the new positions of the scrollbars according to the zoom level ?
  Is it better to implement this using transformations without using a scrollarea?</p>