I am looking for some information about rendering child windows in specific about how OpenGL interop with GDI. The problem that I have is that I have basically is that I have two windows, first, the main windows are created in qt, and inside of qt, a child window is hosted that leverages an OpenGL renderer.
Now what I wanted to do is to host an overlay on top of my OpenGL window, so I use that to overlay the OpenGL window. The problem that I am having is that when I render with OpenGL, the OpenGL generated graphics seem to obscure the graphics area including and effectively undo the graphics composited by qt.
In the image below the blue area is the qt overlay, in that picture I'm using GDI (BeginPaint/EndPaint) so and the windows seem to interact fine. That is, window order seems correct, the client region is correct. The moment I start to render with Opengl the blue area gets replaced with whatever OpenGL renders.
What I did I basically created to create the overlay I created a second frameless, topmost QMainWindow, and once the platform HWND was initialized I reparent it. Basically I change the new windows parent to be the same parent of my OpenGL window.
What I believed this would do is that the every window, gets drawn separately and the desktop composition manager would make the final composition and basically avoiding the infamous airspace problem as documented by Microsoft in their WPF framework.
What I would like to know is what could cause these issues? At this point, I lack understanding why once i render with OpenGL the pixels by qt overlay are obscured, even though windows hierarchy should say make them composited. What could I do to accomplish what I want?
