Problem calling GDI after SwapBuffers()

OpenGL OpenGL: Advanced Coding
1

Hi folks;

I’m working on an interactive modeling program using OpenGL. My application runs on Win32, and I’m using double buffering. Sometimes I need to use GDI to do some drawing on top of the window after I have called SwapBuffers().

I’ve experimented some, and I am coming to the inescapable conclusion that the actual buffer swap is delayed and is happening after I make my GDI calls. Here’s the order of things:

  1. Do OpenGL rendering
  2. SwapBuffers()
  3. glFlush()
  4. GDI calls

And yet it seems that my OpenGL graphics are in fact overwriting the display generated by my GDI calls.

If I insert a long delay between just before calling GDI, then it works as expected.

Can anyone explain what is going on here?

Thanks,
Dan

2

Have you tried to call glFinish instead of glFlush?

3

Perfect. Thanks!

I wasn’t aware of glFinish(), just looked it up. Things work now.