[Bug 768160] qtplugins: How to implement qmlglsrc.

[GStreamer (GNOME Bugzilla)]

https://bugzilla.gnome.org/show_bug.cgi?id=768160

--- Comment #6 from Haihua Hu <jared.hu at nxp.com> ---
(In reply to Matthew Waters (ystreet00) from comment #1)
> qmlglsrc as a screen grabber of the qml scene graph is in general a bad idea
> for performance reasons as you have to perform a readback (bad) of the GL
> front buffer (also bad).  If possible, you should attempt to retrieve your
> rendering before qmlglsink and pass that downstream.
> 
> That being said, it's possible that screen grabbing may be your only option
> so something like that would be useful.

Hi Matthew，

My design of qmlglsrc has no performance concern. 

1. In my code, qmlglsrc will warp qt OpenGL context and I make glcontext shared
with qt warp context so we can copy texture from scene graph to glmemory which
is created in glcontext. This will be very fast because it is operated by GPU. 

2.When scene graph updated, if downstream has not consumed the old buffer and
no new buffer set to qt, just skip this  as we cannot block scene graph.

This will ensure qmlview running smoothly.

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