On Mon, 2012-08-20 at 17:55 -0400, Jean-Sébastien Guay wrote:
> Hi Jeremy, nice to see you back writing graphics code!
I finally have the time again!
> In the past, when I've needed to have a contextID in a custom Drawable,
> I've always gotten it from inside my drawable's drawImplementation. IIRC
> it gets a State pointer and this contains a valid contextID. Same when
> I've needed to create a custom StateAttribute or something, in its
> apply() method it gets a State pointer with a valid contextID or
> something like that.
>
> So you can have a scheme where you defer doing any initialization until
> your first Drawable / StateAttribute needs to be traversed for actual
> rendering, and then you get a valid contextID, do your initialization
> and further ones will use that since initialization has been done already.
>
> You need to make sure you consider the case where your Drawable /
> StateAttribute will be used in multiple contexts. IIRC OSG uses the
> BufferedValue to store resources associated with a context, and I used
> the same pattern. Again IIRC, there were some order of initialization
> issues where I assumed some initialization had been done for a context
> before drawing but it hadn't, but that just involved a bit of pretty
> simple debugging to get fixed.
>
> Hope this helps,
It does. Your use of the word "deferred" is really helpful in this, as
it was a "deferred" approach I was taking and was looking for some
assurance this was an acceptable approach. :)
> J-S
>
>
> On 20/08/2012 12:48 PM, Jeremy Moles wrote:
> > On Mon, 2012-08-20 at 10:44 -0600, Paul Martz wrote:
> >> What you seem to be saying is that you want to set some OpenGL state once
> >> that
> >> applies to all contexts, and not have to set it every frame. AND, you
> >> don't want
> >> to have to add, then remove, a Camera draw callback just to make this
> >> happen).
> >> Is that a good synopsis of the issue?
> > It's close; I don't actually mind using a Camera draw callback for this
> > purpose if it's appropriate.
> >
> > A real summarizing question is: under what conditions is it "safe" to
> > query for support of a particular extension? And what is the preferred
> > API for either fetching or being provided the contextID with which to do
> > this?
> >
> >> You could keep a bool buffered_value that tells you whether or not you've
> >> set
> >> the initial/global state for that particular context. Initially false,
> >> then set
> >> the global state for a context and flip it to true. Would something like
> >> that help?
> >> -Paul
> > Certainly, but I'm still stuck on actually SETTING the state in the
> > first place. :)
> >
> >> On 8/20/2012 10:27 AM, Jeremy Moles wrote:
> >>> Hello everyone! I have a bit of a strange question here, so please bear
> >>> with me. I'll try to be as descriptive as I possibly can, though I'm
> >>> certain I will misuse some terminology.
> >>>
> >>> I am adding support for the NV_path_rendering extension to
> >>> OpenSceneGraph. This extension adds a number of new functions to OpenGL
> >>> when using an NVidia card which take on the form:
> >>>
> >>> glPath{_function_}NV
> >>>
> >>> http://osgnvpr.googlecode.com
> >>>
> >>> In order to create pointers to these new extension functions, I create
> >>> an Extensions object in OSG using the contextID given to me during the
> >>> compileGLObjects method of my overridden Drawable class. This works
> >>> fine, and the code is running as I expect.
> >>>
> >>> https://code.google.com/p/osgnvpr/source/browse/trunk/src/PathCommands.cpp#45
> >>>
> >>> HOWEVER, this paradigm really only works when I need to call extension
> >>> functions associated with an instance (or instances) of my Drawable.
> >>> There are other functions in the NV_path_rendering API that simply set
> >>> global state, and it is with these functions that I'm having difficulty.
> >>>
> >>> The biggest problem here is that in order to get a pointer to the
> >>> Extensions static object, I need a valid GraphicsContext contextID.
> >>> However, I've tried a number of methods to obtain one of these, but
> >>> every attempt I make actually breaks the entire codebase. I wish I could
> >>> explain it better than that...
> >>>
> >>> For example, if I try to use some code like the following:
> >>>
> >>> ------------------------
> >>>
> >>> Windows windows;
> >>>
> >>> viewer.getWindows(window);
> >>>
> >>> cID = windows[0]->getState()->getContextID();
> >>>
> >>> osgNVPR::getNVPRExtensions(cID);
> >>>
> >>> -------------------------
> >>>
> >>> ...then I seem to get an invalid contextID and all subsequent attempts
> >>> to use that contextID (even by OSG itself) won't work. The entire
> >>> rendering process seems to be broken in this manner.
> >>>
> >>> If instead I create a Camera::DrawCallback object and use the RenderInfo
> >>> there instead, then everything works fine. However, I feel like I'm
> >>> grossly misusing a Camera::DrawCallback just to set and unset state...
> >>>
> >>> My question is: if I need to set global state like this once, somewhere
> >>> high in the scenegraph, what is the best way--keeping in mind that I
> >>> also need a valid contextID in order to access my Extensions functions
> >>> per-context?
> >>>
> >>> Thanks!
> >>>
> >>> _______________________________________________
> >>> osg-users mailing list
> >>> osg-users@lists.openscenegraph.org
> >>> http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org
> >>>
> >>>
> >> _______________________________________________
> >> osg-users mailing list
> >> osg-users@lists.openscenegraph.org
> >> http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org
> >
> > _______________________________________________
> > osg-users mailing list
> > osg-users@lists.openscenegraph.org
> > http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org
> >
>
>
_______________________________________________
osg-users mailing list
osg-users@lists.openscenegraph.org
http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org
