[Bug 704809] Use one GstGLContext per streaming thread

[GStreamer (bugzilla.gnome.org)]

https://bugzilla.gnome.org/show_bug.cgi?id=704809
  GStreamer | gst-plugins-gl | git

Julien Isorce <julien.isorce> changed:

           What    |Removed                     |Added
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                 CC|                            |julien.isorce at gmail.com

--- Comment #1 from Julien Isorce <julien.isorce at gmail.com> 2013-08-26 16:34:57 UTC ---
In the actual gst-plugins-gl 1.0 can we can create a gl context without a
window ? If no then we have to add this feature if it's really possible. I mean
can we share 2 gl contexts if one is setup with off-screen and the other with
on-screen surface ?

Anyway I'm wondering if we could use the streaming thread as the gl thread
(except for the final drawing thing done by glimagesink). See solution 2.

For example in videotestsrc ! gleffect ! queue ! glfiltercube ! glimagesink
there are 2 streaming threads, the first one (called A) involved in
videotestsrc ! gleffect, and the second (called B) involved in queue !
glfiltercube ! glimagesink


1) The first improvement would be to create one GstGLContext A for the
streaming thread A, shared with the GstGLContext B for the streaming thread B.
In this case it would have 2 streamings thread and 2 GL threads (1 GL thread
per GstGLContext)

2) The second improvement would be to use the streaming thread as a GL thread.
In our example, streaming thread A would be the GL thread associated with
GstGLContext A. Streaming thread B would be the GL thread associated with
GstGLContext B. Then we would still need another GL Thread with GstGLContext
created by glimagesink for drawing purpose.

With this second solution we would need the ability to be able to create a
GstGLContext without creating a new thread and without running a loop into it.
Just call make current and other gl calls directly in that thread :)


** With solution 1) and 2) we would need to know in which streaming thread we
are in GST_QUERY_CONTEXT. If we are in the same then we use it directly but if
we are in an other streaming thread then we share. How to do that ? Improve
GstContext ? Is there a GST_QUERY_STREAMING_STATUS ? I only saw examples with
messages.

With solution 2) we would also need to be able to ask for calling a callback
into the streaming thread. I mean if we need to ask for calling a GL function
in the streaming thread from set_caps (or get_caps or any other function of an
gl element) . Not sure if it is possible as the GstTask does not run
g_main_loop so we cannot use g_timeout_callback for example.

An other question, in GstBaseTransform, which virtual methods are "100%
garanti" to be called in the streaming thread the element belong 
?http://gstreamer.freedesktop.org/data/doc/gstreamer/head/gstreamer-libs/html/GstBaseTransform.html
Only (*transform) ?

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