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>
In order to use oes-external, the qml6glsink needs a fragment shader that uses
the samplerExternalOES.
The qsb tool is not able to handle shaders that contain samplerExternalOES since
this feature is not supported by all target shading languages. The qsb tool is
able to replace a shader in the qsb file to handle this use case. Use it to
generate a shader variant that uses samplerExternalOES for OpenGL ES and select
that variant if the qml6glsink negotiated texture target oes-external.
Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/7319>
* RED_OR_ALPHA8 will map value to alpha for OpenGL, use R8 to avoid
2nd shader
* Determine texel size for proper texture memory preparation
* QByteArray::fromRawData() does shallow copy and thus leads to use of
corrupted memory
* Make sure RGBA dummy texture is fully opaque
* QRhiTexture::create() must be called to allocate texture resources
Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/6578>
