[Development] QtCS: OpenGL session notes

[Sean Harmer]

On Monday 25 June 2012 11:44:09 Girish Ramakrishnan wrote:
> Hi,
> OpenGL session notes (pasted from
> http://qt-project.org/groups/qt-contributors-summit-2012/wiki/QtOpenGL)
> so you can comment inline.

Sorry I could not attend this year but the QtCS clashed with my family 
vacation.

> Thanks to Samuel for leading the session and taking the notes!
> 
> Girish
> 
> Future plans
> - Desktop OpenGL 3+ support, ES 3 support

I have started work on this (desktop for now until ES 3 is released). The 
general idea is to make it as simple as possible to get up and running with 
OpenGL and Qt without having to resort to manually resolving entry points or 
trying to mix in GLEW or similar.

I have written a small parser for the OpenGL spec files. The idea is to use 
the parsed information along with a code generator to create a family of 
classes (API still being determined) similar to QOpenGLFunctions. 

These classes will contain functions for each OpenGL version and profile. 
QOpenGLContext could be modified to return a pointer to the class appropriate 
for the requested context.

This has the advantage of having access to OpenGL functions per context (entry 
point addresses can change between contexts on some platforms) and providing 
compile-time errors if you try to use functions not present in a given version 
and profile (e.g. glBegin() with an OpenGL 3 Core Profile context).

Aspects that still require some thought are how to incorporate OpenGL 
extension entry points and higher level "is feature X available". For the 
latter, a given feature may be provided either by the core functionality in 
some versions of OpenGL or by extensions in earlier versions. This kind of 
query is needed to re-enable support for Geometry shaders and to introduce 
support for Tessellation shaders in QtGui.

I also have some ideas (and some code cooking) for other "enabler" classes 
e.g. QOpenGLVertexArrayObject.

> - QOpenGLWindow

Yes this would be a useful convenience class to have.

> - Shared cross process graphics buffer APIs
>  - copy to texture
>  - bind to texture

Along these lines it would be nice to have OpenGL texture formats as storage 
formats in QImage. There is also no replacement in QtGui for 
QGLWidget::convertToGLFormat() as yet.

Cheers,

Sean