title: gtk+ Image draw over image in c++
body: <p>I would like to draw a simple (red) line <strong>over</strong> an image with gtkmm (in c++).</p>
  
  <p>I have the image : <code>Gtk::Image *image</code> which is displayed in my window.</p>
  
  <p>But I would like the line to change of position (I mean : draw another line) when a function is called. I need your help because I didn't find how to draw <strong>over</strong> an existing image...</p>
  
  <p>Thank you for your help !</p>
  
  <p>EDIT : A solution for me would be to overlay the image by an image with alpha channel... but I don't know how to to that :-/</p>