[Qt-interest] Fwd: QGLContext error

[ami guru]

Hello Oliver,

I did try off-screen rendering using FBO(Frame buffer Object). It worked
fine.

Probably i have to give 4.5 a try


Thanks
Sajjad

---------- Forwarded message ----------
From: <Oliver.Knoll at comit.ch>
Date: Fri, Jan 9, 2009 at 1:23 PM
Subject: Re: [Qt-interest] QGLContext error
To: qt-interest at trolltech.com


ami guru wrote on Friday, January 09, 2009 1:10 PM:

> ...
> Whenever i try to render to pixmap i get the following error:
> ...
> QGLContext::makeCurrent(): Failed.
> ...
> Any hint to get around that ?

Try upgrading the OpenGL driver maybe? It's sad to say, but mostly on Linux
it is the driver's fault, especially for newer cards where the driver has
not gone through an extensive testing phase yet (read: not too many
customers have complained about it so far and the ones who are actually
using it can be happy that there exists one at all ;)

That said, you could also give a recent Qt 4.5 snapshot a try - I understand
they improved the OpenGL there, too. When it comes to rendering QImages onto
a QGLWidget, for example, making better use of OpenGL extensions (I see a
*dramatic* perfomance boost on my WinXP laptop with some nVidia graphic card
when rendering a "non-power-of-two" pixmap, for example :) - but I doubt
that has anything to do with the problem you are observing. Still, it's
worth a try.

You could also try another OpenGL application which renders offscreen into a
pixmap. Note though that if it works it *still* does not imply that it is
Qt's fault, because there are *several* ways in OpenGL to render to a
pixmap!. But if it fails there as well it would be a clear indication that
it is indeed the driver's fault.

Cheers, Oliver
--
Oliver Knoll
Dipl. Informatik-Ing. ETH
COMIT AG - ++41 79 520 95 22

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