[gst-devel] Querying GL context pixel format

[Julien Isorce]

2009/11/4 Andrey Nechypurenko <andreynech at yahoo.com>

> Hi,
>
> > set GST_GL_WINDOW_DEBUG=1
> > before launching the pipeline, it should output some debug informations
> about
> > success or failure when sharing gl contexts.
>
> Sorry for such a question, but where this output goes on Windows? I do not
> see anything neither in console nor in MSVC output window where debug
> messages are usually printed. Or maybe it is because I am using "release"
> version of gstreamer DLLs?
>

open a console then just type:  set GST_GL_WINDOW_DEBUG=1
(as you can also do: set GST_DEBUG=gldisplay:3
and
set GST_GL_SHADER_DEBUG=1)
then enter your pipeline as usually.

have you tried this build
http://www.gstreamer-winbuild.ylatuya.es/doku.php?id=download ?
The debug works with this build.

>
> > I had no time to look into your example. I am still busy right now.
>
> No problem. I've learned a lot trying to fix the problem myself and proud
> that it works at least on Linux :-) .
> None of these would happen if you fixed the error earlier :-) .
>

[?]


>
> > What I can say, if the debug is : failed to share gl context, make sure
> that the
> > Qt GL context is not current in any thread when sharing it with
> gstreamer. (see cluttershare
> > and sdlshare (from git) examples to see how to do that)
>
> Well, I am explicitly calling wglMakeCurrent(0, 0); before initializing
> gstreamer to unset Qt context. Since it also works on Linux, I assume that
> the initialization sequence is correct. That is why I was looking for other
> reasons which might prevent context sharing, i.e. different pixel

formats.
>
No pb about pixel format because it the same screen. So even if the input
values are differents then the s&ame is choosen. Something like that.


>
> Nevertheless, is not it a kind of co-accidence that on Linux Qt initializes
> the context in exactly the same way as gstreamer does? And do not you think
> that the more robust way would be to query the context created by gstreamer
> and explicitly instruct Qt (or whatever other library) to create the same
> context format to ensure that sharing will work? If yes, then the
> corresponding API or callback might be necessary as I mentioned in my
> previous email.
>

Actually I think it's just a symetric pb. But it could be a possibility.
Well about the pb, on window the sharing can be done after context creation,
(on linux, it's done when creating a context)
but bettween the creation and the sharing, no texture, no shaders, no fbo or
nothing else must be created before sharing the 2 contexts.
(that's why the possibility the share the gl context after the creation has
(as far as i know) no sense.
Anyway, you could use on opengl debugger and see if on windows, qt is
creating a texture or anyelse before sharing it.

Sincerely
Julien


> Sincerely,
> Andrey.
>
>
> 2009/11/4 Andrey Nechypurenko <andreynech at yahoo.com>
>
> >Hi Folks,
> >
> >>I am currently working on Qt-based application which uses OpenGL context
> (texture) sharing technique to display video on 3D scene. I am using
> approach similar to the one implemented in cluttershare example from
> gst-plugins-gl. Currently it runs on Linux but does not work on Windows. I
> believe that the reason is that context sharing between Qt and Gstreamer
> does not work. According to the documentation, only contexts with the same
> pixel format could be shared. That is why I was looking for the way to query
> pixel format used with GL context created by gst-gl plugin and did not found
> it yet. I guess it just does not exists :-) .
> >
> >>So the question I would like to ask is whether it would make sense to add
> some kind of API to make it easier to access GL context created? For
> example, it could be callback set via certain property which is called right
> after the initialization step and provide corresponding handles (HWND, HDC,
> HGLRC or any other platform-specific handles similar to those stored in
> _GstGLWindowPrivate structure) which could be used with platform and GL API
> to query required information?
> >
> >>I would also appreciate any comments or pointers to the possible solution
> directions without extending the property set or API.
> >
> >>Regards,
> >>Andrey.
> >
> >
> >
> >
>
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