[osg-users] context IDs

[Robert Osfield]

Hi Andy,

I have just had a quick look at the various s_* containers in
GLExtensions.cpp and I think these are an old hang over that should be
removed and replaced by code that is embedded into the GLExtensions
object so that it can be constructed and destructed.

Short of this refactor perhaps these data structures could be reset
within the GLExtensions destructor.

I don't have time to look into a fix right now, so either dive into
the code yourself or avoid creating and destructor lots of contexts.

Robert.

Robert.
On Wed, 19 Sep 2018 at 15:52, Andy Skinner <Andy.Skinner at mathworks.com> wrote:
>
> OK, I've digested some more.  I see what you mean (I think) about ~State clearing the GLExtensions object from the static map (s_extensions) defined in GLExtensions.cpp.
>
> However, if the next GLExceptions::Get will make a new one, the GLExtensions constructor will use other static maps: s_glExtensionSetList, s_glRendererList, and s_glInitializedList.  So if we make a new GLExtensions object, we will get the answers from last time, because they were cached.
>
> It seems to me that if we need to store these per context ID, and if we can re-use context IDs, then we need a way to clear out what is stored, possibly when the context ID usage count goes to 0, or maybe explicitly.
>
> thanks
>
> andy
>
> -----Original Message-----
> From: osg-users <osg-users-bounces at lists.openscenegraph.org> On Behalf Of Robert Osfield
> Sent: Wednesday, September 19, 2018 4:20 AM
> To: OpenSceneGraph Users <osg-users at lists.openscenegraph.org>
> Subject: Re: [osg-users] context IDs
>
> Hi Andy,
>
> It's quite a while since I worked specifically on the osg::State, ContextID, osg::GLExtensions management.  In principle it should be possible to reuse ContextID's, the sticky issue of whether the GLExtensions object is recreated for each new graphics context is something I haven't personally tested.  Looking at osg::State is does look to clean up the GLExtensions object in 3.4 onwards (I haven't checked further back)
>
> For graphics performance I would recommend that applications don't go creating and destroying GraphicsWindows, if possible just hide the window and reuse it will provide better performance.
>
> Cheers,
> Robert.
> On Mon, 17 Sep 2018 at 19:08, Andy Skinner <Andy.Skinner at mathworks.com> wrote:
> >
> > If we get our contextIDs from GraphicsContext::createNewContextID(), it could give us a new number or return a previous one, if we are returning them with GraphicsContext::decrementContextIDUsageCount.  Right?
> >
> >
> >
> > Is there an intended connection between a contextID that has been used and a new one?  It looks to me that extensions are stored per context ID and never reset.
> >
> >
> >
> > So if we change something about what we are looking for in the context (sometimes we fall back to software OpenGL for testing or helping a customer through an issue), we might reuse a context ID, but still have extensions associated with the ID that are not appropriate for it.
> >
> >
> >
> > Am I missing an assumption here?  Should I be able to reuse a contextID for an unrelated context?  If not, I'll just remove call to decrementContextIDUsageCount.  That means the number and various maps will continue to grow.
> >
> >
> >
> > thanks
> >
> > andy
> >
> >
> >
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