Qt-interest Archive, November 2006
Re: Multiple GL contexts in Qt 4.2 not working
Message 1 in thread
First of all, thanks to all, who were helping me.
I just solved the problem. It is either a bug or a feature in Qt 4.2 :-)
Maybe Qt developers can comment on it.
Ok, here is the problem description:
updateGL() calls makeCurrent() internally (you can found the source code for
this in qgl_win.cpp in the class QGLContext). makeCurrent() internally calls
GetDC(). So far so good.
Eevery call to GetDC() MUST have a corresponding call to ReleaseDC().
ReleaseDC() is usually called in doneCurrent(). doneCurrent() is supposed to
be called automatically by Qt. However, in our application Qt DID NOT call
doneCurrent() automatically, but only makeCurrent(), causing many many calls
of GetDC() without corresponding calls of ReleaseDC(). If the numer of
GetDC() calls exceeds some limit, a null pointer is returned by Windows.
So the temporary solution in our application is to replace every updateGL()
call by updateGL() followed by doneCurrent().
Qt developers, is this behaviour intended or is it a bug?
Unfortunately I don't have the 4.1 source available at the moment to debug
the behaviour, but apparently Qt 4.2 introduced this incorrect behaviour.
Thanks for your considerations!
Cheers,
Marco
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Message 2 in thread
Hi,
> Qt developers, is this behaviour intended or is it a bug?
> Unfortunately I don't have the 4.1 source available at the moment to debug
> the behaviour, but apparently Qt 4.2 introduced this incorrect behaviour.
I don't work on the Windows platform so I can't comment, but you might
want to ask Trolltech support or file a bug report (preferably with a
minimal compilable example) and someone will look into this:
http://www.trolltech.com/bugreport-form
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Message 3 in thread
The bug is filed:
http://www.trolltech.com/developer/task-tracker/index_html?method=entry&id=138570
Marco
> I don't work on the Windows platform so I can't comment, but you might
> want to ask Trolltech support or file a bug report (preferably with a
> minimal compilable example) and someone will look into this:
> http://www.trolltech.com/bugreport-form
>
> --
> Dimitri
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