[Development] OpenGL Support in Qt5

[Sean Harmer]

On Saturday 21 July 2012 09:50:25 Sean Harmer wrote:
> On Monday 16 July 2012 20:22:24 Sean Harmer wrote:
> > On 16/07/2012 19:54, gunnar.sletta at nokia.com wrote:
> > > On Jul 16, 2012, at 4:54 PM, ext Sean Harmer wrote:
> > >> On Monday 16 July 2012 07:21:23 Thiago Macieira wrote:
> > >>> On segunda-feira, 16 de julho de 2012 15.12.15, Sean Harmer wrote:
> > >>>> On Monday 16 July 2012 07:08:38 Thiago Macieira wrote:
> > >>>>> I'm asking for Qt 5.0: what should we tell Linux distributors to
> > >>>>> configure
> > >>>>> qtbase with? Considering what requirements qtwayland has, I think it
> > >>>>> needs
> > >>>>> to be -opengl es2.
> > >>>>> 
> > >>>>> Correct?
> > >>>> 
> > >>>> If using wayland then yes I believe so.
> > >>>> 
> > >>>> If using xcb backend then -opengl desktop works fine.
> > >>> 
> > >>> There's only one build of Qt. The choice is made at compile-time of
> > >>> qtbase,
> > >>> not at run-time like the platform plugin.
> > >>> 
> > >>> So everyone should use OpenGL ES 2.
> > >> 
> > >> Unless they want to support applications that use legacy OpenGL calls
> > >> or
> > >> develop new applications that use modern desktop GL.
> > >> 
> > >> There seems to be a dependency issue here that needs resolving. Qtbase
> > >> itself has a configure time switch for OpenGL ES vs Desktop whereas the
> > >> QPA plugins can be decided upon at runtime. Is there some way we can
> > >> move the GL decision to be runtime too I wonder?
> > > 
> > > We've talked about in the past that Qt could internally resolve all
> > > OpenGL
> > > functions and expose proxy functions which at run time are linked
> > > towards
> > > the correct library... Incidentally, exactly the problem the patch that
> > > started this thread solves, if it gets expanded to include every
> > > extension in the Khronos registry.
> > 
> > I almost have this aspect completed now. Should be done in the next day
> > or so. Once ready I'll update the patchset.
> 
> The patchset now contains the output of the code generator including support
> for all OpenGL extensions in the Khronos registry (for those that actually
> define entry points).

As a real world example of how this could be used in Qt5, this patch:

https://codereview.qt-project.org/#change,31231

re-enables geometry shader support in a more flexible way than in Qt4. The new 
approach can use geometry shader support built into newer versions of OpenGL 
(3.2 or newer) or using one of the extensions GL_ARB_geometry_shader4 or 
GL_ext_geometry_shader4.

It should be trivial to additionally add support for tessellation shader 
stages in a similar manner.

Cheers,

Sean