title: Transparent window above OpenGL
body: <p>My application have OpenGL Engine in a WPF hosted Window.
  I created half-transparent widget (as Window object) that should display content above OpenGL window. Sometimes when application processing data, widgets backgrounds becomes black (see attached image).
  Does anybody know what it is. How can I resolve this problem.<img src="https://i.stack.imgur.com/c358C.png" alt="enter image description here"></p>