Scenario is that there are two (or more) GstGLContext's wrapping Qt's GL
context from either multiple qml(6)glsink or qml(6)glsrc elements. Call flow is this:
1. material 1 setBuffer()
2. material 1 bind()
3. material 2 setBuffer()
4. material 2 bind()
If the call to setBuffer() reuses the same buffer as previous call, then the
qt context is not updated in the material. If however the previously used qt
context by the material had been deactivated or freed, then bind() would fail
and could result in a critical like so:
gst_gl_context_thread_add: assertion 'context->priv->active_thread == g_thread_self ()' failed
Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/7970>
Issue was that Qt was caching multiple different shadersbased on a static
variable location. This static variable location was the same no matter
the input video format and so if an item had an input video format of
RGB and another of RGBA, they would eventually end up using the same
GL shader leading to incorrect colours.
Fix by providing different static variable locations for each of the
different shaders that will be produced.
Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/5145>
