The depth cueing through GL fog has been broken for a long while, now.
The fog-related API in Clutter is ridiculously limited, and harks back
to simpler times; the ClutterFog structure is not enough to express all
the GL fog machinery, and required application code to connect to the
Stage's paint implementation and drop into Cogl directly.
Additionally, the fixed pipeline fog machinery in GL simply does not
work with premultiplied alpha, unless you use a shader - and in that
case it would only work for textures. Let's deprecate it, and just
don't do anything if somebody has the brilliant idea of setting the
:use-fog property to TRUE.
The clutter-stage.h header still has a bunch of macros that have, for
reasons unknown[*], survived the 1.0 API cut and have long since been
deprecated. Let's hide them under the deprecated/ carpet and let us
never speak of them ever again.
[*] pretty sure alcohol or other psychotropic substances were involved
but I take the 5th on that.
