OpenGL vs. Qt4 OpenGL

[Andreas Pakulat]

On 13.12.07 17:53:49, Allen Winter wrote:
> On Thursday 13 December 2007 14:54:28 David Faure wrote:
> > On Thursday 13 December 2007, Allen Winter wrote:
> > > Howdy,
> > > 
> > > I don't think our buildsystem handles the OpenGL you can
> > > build in Qt4 vs. the one that comes with a distro.
> > 
> > I don't understand. This isn't like libpng which can be part of Qt...
> > OpenGL is not "part" of Qt, Qt only has OpenGL support when that's enabled.
> > i.e. Qt itself uses the OpenGL that comes with your distro, and I guess KDE
> > only uses Qt OpenGL (QGLWidget), otherwise KDE could make some opengl
> > calls but couldn't display the result inside a QWidget... pretty useless.
> > 
> 
> What is libQtOpenGL.so that I find in my qt-copy/lib?

Thats Qt's OpenGL support, in particular QGLWidget and whatever it
needs. If you check with ldd, you'll see that this one links against
your system libGL.so.

> And how does it differ from /usr/lib/libGL.so that I also find on my system?

Thats your OpenGL library, the one that provides stuff such as glXXX
methods.

> kpat links against ${QT_QTOPENGL_LIBRARY}, which points to qt-copy/lib/libQtOpenGL.so
> 
> so this is why I'm confused.  I do have 2 separate OpenGL builds available.
> 
> should we permit stuff to build against QT_QTOPENGL?
> so far, the only instance I've seen of this is in kpat

I'm not into that stuff that much, but I think things like kwin that
want to render directly onto the screen with OpenGL need to link only
against libGL, not against libQtOpenGL. 

If an app however only wants to display an OpenGL scene inside a QWidget
then it primarly needs QtOpenGL. (the libGL is automatically pulled in
through the deps).

Andreas

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