title: Drawing overlay on screen in C++ or Java
body: <p>Is there any way to draw an invisible overlay on top of the screen (meaning in front of all windows and everything else) in C++ and/or Java?
  It doesn't need to support 3D graphics or anything fancy, I just need to be able to draw 
  lines/pixels on it.</p>
  
  <p>There are some other solutions that I found on the internet, but they all either</p>
  
  <p>1) don't allow mouse clicks to go through them (onto the windows or other stuff under it) or</p>
  
  <p>2) are only for Windows (I need something that works on Windows and Linux, but Mac support would also be nice).</p>