title: Mixing OpenGL and GDI on Windows
body: <p>I'm trying to work out a way to mix OpenGL rendering and GDI in Windows. Previously I've been rendering my OpenGL contents into a framebuffer object, extracting it and then blitting it into the windows GDI graphics context and then drawing my GDI stuff over the top. This is really crippling the framerate.</p>
  
  <p>I'd like to do the opposite to what I am doing now, so my OpenGL rendering is done directly to the window and then I render GDI stuff to a bitmap which is uploaded to a texture and then overlayed using a quad. The GDI stuff doesn't change all that much so I don't need to redraw it every frame, I can just cache the texture.</p>
  
  <p>I can almost get it working, the problem is that I can't seem to get the correct alpha values from the GDI bitmap so text and lines get horrible jaggies.  </p>
  
  <p>Does anyone have any useful resources for how to do this? Is it even possible to get GDI or GDI+ to write to the alpha channel in the way I need?</p>