[osg-submissions] Reuse of context IDs and cleanup of OpenGL resources.

[Robert Osfield]

Hi Mark and Mathias,

Thanks for the extra explanation, its useful to get an insight on
where things are failing.

On Wed, Apr 16, 2008 at 7:35 AM, Mathias Fröhlich
<M.Froehlich at science-computing.de> wrote:
>  Wouldn't it be better to stick such objects and cached information into the
>  GraphicsContext class? Then they get deleted, once they are no longer
>  valid ...

One design change I have been considering for a couple of years is to
move GL object ID management from the local StateAttribute/Drawable
classes into osg::State.  Extensions being per context could also get
the same treatment.  It would require us maintain a unique ID per
StateAttribute/Drawable, which is used as look up to the GL objectID.

The reason to put it into osg::State rather than GraphicsContext is
that now all apps use osgViewer, and osg::State purpose is to track
OpenGL state so conceptually its the right place, and finally all the
apply()/draw() methods get pretty direct access to osg::State via the
RenderInfo structure.

This new design would solve the issues of deleting contexts, as one
would delete the osg::State object for the context, and there would be
no need to go cleaning the scene graph as there is no actual OpenGL
obejcts in the scene graph itself, just a ID which stays constant for
the life of the object.

Given how close 2.4 is, its not possible to put such sweeping changes
in.  I believe above design is the right way to tackle this  problem
(as well as others), and also believe that merging extra workaround
code for the limitations of the current design would just complicate
the existing code and make it even more awkward to maintain.

I will tackle the above design change in the 2.6 round.  I'd expect
it'd be about a weeks work.

Robert.