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X: wglMakeCurrent error: 0006 on XUnmapWindow->XMapWindow

I was asked by the freeglut mailing list to alert the X/Cygwin
team to problems with the WGL context handles becoming invalid
if a window is hidden and then the error in the subject is out
putted when the window is revealed again.

There are also issues with iconification, where the windows are
in need of repainting when restored. But when unmapped they lose
their WGL context, meaning that OpenGL textures are probably lost
and the context is inoperable, which is a whole other class of 

The freeglut developer Chris Marshal confirmed this experience.
There is a resizer.exe demo in the freeglut development package
that demonstrates both problems.

In GLUT the problem presents itself when doing glutHideWindow and
then glutShowWindow. Which is not the same as XIconfiyWindow.

I hope this is a temporary development and not the state of X on
Cygwin. I found Xming to supplement the X server. I spent a couple
afternoons attempting to determine the root of the problem. I 
thought perhaps the backing-store fields needed to be set, but it
became clear that most X servers are simply very lenient and most
clients expect them to be, and that there's most likely oversights
in Cygwin/X in the direct rendering mode with WGL.

P.S. I have not subscribed to the Cygwin mailing list. You know if
I receive a CC, but I'm just throwing this out. It may well not be
the first report. Thank you :)

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