Dana and I worked through some OpenGL setup stuff, and we got C++ OpenGL calls rendering to my .NET control. I get the HDC in C# from the PaintEventArgs, and pass the HDC through to my C++ OpenGL rendering code... and it draws! Mostly.

With my current code, I only see the opengl-painted stuff when I minimize, then maximize the window; my opengl code gets called every paint event, but it only gets drawn visibly after a maximize event. I'm not yet very worried about this, because I'm making a new wglContext every paint event, which is not ideal. My next step is to make one wglContext for a ManagedWindow, and reuse it for subsequent redraws.

Here's the most important nugget of the code

// C#
// Paint handler for my .NET control
private void LeoControl_Paint(object sender, System.Windows.Forms.PaintEventArgs e)
{
System.IntPtr hdc = e.Graphics.GetHdc(); 
// Call the C++ internals to render some stuff onto this widget.
CSCppWrapper wrapper = new CSCppWrapper();
// initHDC also draws some test stuff into the HDC
wrapper.initHDC(hdc);
e.Graphics.ReleaseHdc(hdc);
}
// C++
void
CppInternals::initHDC(HDC hdc) 
{
 _hdc = hdc;
 //   create and enable the render context (RC)
       _hrc = wglCreateContext( _hdc );
 PIXELFORMATDESCRIPTOR pfd;
 int format;
  
 // set the pixel format for the DC
 ZeroMemory( &pfd, sizeof( pfd ) );
 pfd.nSize = sizeof( pfd );
 pfd.nVersion = 1;
 pfd.dwFlags = PFD_DRAW_TO_WINDOW | PFD_SUPPORT_OPENGL | PFD_DOUBLEBUFFER;
 pfd.iPixelType = PFD_TYPE_RGBA;
 pfd.cColorBits = 24;
 pfd.cDepthBits = 16;
 pfd.iLayerType = PFD_MAIN_PLANE;
 format = ChoosePixelFormat( _hdc, &pfd );
 SetPixelFormat( _hdc, format, &pfd );
 renderScene();
 
 // pair with create context call.
 wglDeleteContext( _hrc);
}
void
CppInternals::renderScene() {
 // Tell it to render to the context we initialized in initHDC
    wglMakeCurrent( _hdc, _hrc );
 .
 .
 .
        // make some opengl calls here to draw stuff
        // ....
 .
 .
 .
 // Actually put this opengl stuff on the screen!
 // Except, this doesn't seem to actually put the stuff on the screen... I don't think. 
 SwapBuffers(_hdc);
 // Let go of this context
 wglMakeCurrent( NULL, NULL);
}

This makes me so very very happy.