title: How can I make another application's window transparent?
body: <p>I know how to make my own application transparent using Layered Windows but I want to make a different application transparent (for example notepad).
  I wrote code like this but it doesn't work with other windows except my app main window:</p>
  
  <pre><code>SetWindowLongPtr(WindowFromPoint(p), GWL_EXSTYLE, 
                   GetWindowLongPtr(hWnd, GWL_EXSTYLE) | WS_EX_LAYERED);
  SetLayeredWindowAttributes(WindowFromPoint(p), 0, (255 * 50) / 100, LWA_ALPHA);
  </code></pre>
  
  <p>where p is a point on screen ( for example the window I select with my mouse )</p>
  
  <p>I am also interested if there is a way to do this directly from Windows 7 (not necessarily programmatic). I figure there must be a way to do it since every application is rendered in it's own surface and DWM composites them into the final image.</p>