The depth buffer is marked as invalid when 1) the framebuffer is just created,
and 2) whenever GL_DEPTH_TEST is enabled on it. This will ensure the
framebuffers attached depth buffer (if any) is properly cleared before it's
actually used, while saving needless clears while depth testing is disabled
(the default).
https://bugzilla.gnome.org/show_bug.cgi?id=782344
CoglOffscreen is effectively a CoglFramebuffer, but it isn't being marked as
such by the GType machinery. This makes it impossible for introspection to
correctly set this class up.
Fix that by adding a COGL_GTYPE_IMPLEMENT_INTERFACE() code into the declaration
of CoglOffscreen. This does not have any functional changes though.
In cogl use cogl-config.h and in clutter use clutter-build-config.h. We
can't use clutter-config.h in clutter because its already used and
installed.
https://bugzilla.gnome.org/show_bug.cgi?id=768976
