title: Draw polygons, and calculate areas
body: <p>I'm looking for a code that allows to draw polygons, with the mouse, and to calculate the surface.
  As well as selecting an angle and moving it to transform the shape.
  PS: I managed to draw lines between different points and close them to create a polygon.
  But I can not select the points to transform the polygons.</p>
  
  <p>My question is: Is there anyone who has already invented this wheel ?</p>
  
  <p>Cordially.</p>