Zooming into particular part of Screen

Hi Guys,

I have attached a screenshot of my virtual world and what I wish to achieve.My Virtual World looks like screenshot 1 and if the user highlights a section of the screen with a mouse(like the red rectangle shown) ,i want the screen to show only that portion of the virtual world on the whole window.

I thought of ofFBO and screentodata but was wondering if there would be a more efficient solution ?

Thanks !