[Texmap][GStreamer]: Map video frames as early as possible and wait via GL sync meta before using texture ids

[Víctor M. Jáquez L.]

This report is inspired on https://gitlab.freedesktop.org/gstreamer/gst-plugins-base/commit/b5aa304f201d0805de2b33ab97d293654baa12cd?merge_request_iid=156

We should fence [1] the texture to render in its internal GL context, and wait [2] for its rendering in our application GL context, otherwise the GL pipeline could be working on the texture when painting it.

1. https://www.khronos.org/registry/OpenGL-Refpages/gl4/html/glFenceSync.xhtml
2. https://www.khronos.org/registry/OpenGL-Refpages/gl4/html/glWaitSync.xhtml

[Víctor M. Jáquez L.]

Well, I guess this enhancement doesn't make much sense since it uses OpenGL API 3.5 while webkitgtk uses 3.0

[Philippe Normand]

Could this be useful for WPE though?

[Philippe Normand]

For EGL there's an equiivalent but it doesn't seem to be supported in GStreamer:

https://www.khronos.org/registry/EGL/extensions/KHR/EGL_KHR_fence_sync.txt

[Víctor M. Jáquez L.]

(In reply to Philippe Normand from comment #3)
> For EGL there's an equiivalent but it doesn't seem to be supported in
> GStreamer:
> 
> https://www.khronos.org/registry/EGL/extensions/KHR/EGL_KHR_fence_sync.txt

If I understand correctly, at least in i915, the implementation is the same for  both 

https://gitlab.freedesktop.org/mesa/mesa/blob/master/src/mesa/drivers/dri/i915/intel_syncobj.c#L30

And in another spec I read that the glFenceSync spec is newer, thus it is expected to cover the EGL usage.

[Víctor M. Jáquez L.]

Reopening because it's required for other context, specially on EGL.