My goal in this case is to get best support on pure Wayland (without XWayland), where EGL is used. Mesa only supports GLES2 for EGL, not full GL. The typical USE flag setup would thus be
-opengl +egl +gles2
(although some maintainers consider all that a part of OpenGL which is then +opengl, as well)
Strangely, gst-plugins-bad has a constraint egl ( !gles2 ) which doesn't appear to make much sense to me in the first place (maybe someone could clarify this or is this a separate bug?). Second to that, egl support for gst-plugins-vaapi with the egl USE flag requires gst-plugins-bad[opengl] which in turn demands !gles2, as well.
I'm unsure as to what exactly is the bug here, perhaps just a set of contradictory terms. In any event, it appears to be impossible to get the correct EGL/GLES2 support on Wayland through these USE flags.
I think the problem is in gst-plugins-bad
*** This bug has been marked as a duplicate of bug 525936 ***
Are you sure about the gst-plugins-bad[opengl] requirement? I'm not sure that's covered there. I think the correct dependency of gst-plugins-vaapi[egl] should be gst-plugins-bad[egl].
Reopening this one as a reminder to myself to fully figure out the opengl/egl/gles2 USE flag story in general and in the gst-plugins-bad context and then possibly tweak what's needed (if anything) for bad, vaapi and more with the 1.10 bump to be done soon.