* clutter/cogl/cogl.h: Add cogl_fog_set() abstracting the
glFog() functions and enabling the GL_FOG flag.
* clutter/cogl/gl/cogl.c: Add GL implementation of cogl_fog_set().
* clutter/cogl/gles/cogl.c: Add GL/ES implementation of
cogl_fog_set().
* clutter.symbols: Add new symbols.
* clutter/clutter-stage.h: Add API to enable depth cueing on
the stage using a linear GL fog, and to set the parameters
for it (#637).
* clutter/clutter-stage.c (clutter_stage_paint): Enable the
GL fog if the ClutterStage:use-fog property is true.
* tests/test-depth.c: Test the new stage API.
* clutter/clutter-behaviour-depth.c:
Modify to work like all other behvaiours in not forcing
increasing order in behaviour 'limits'. (#436)
Rename limit min/max props to start/end.
* tests/test-depth.c:
Simplify test-case to work with above change and
without multiple ramps
* clutter/clutter-behaviour-rotate.c:
Handle CW rotation when end > start and similar for CCW just
like ellipse behaviour.
* clutter/clutter-behaviour-depth.c: Clarify that what drives
the movement along the Z axis is the ClutterAlpha object (we
don't have the luxury of a rollover like the opacity does);
so, if you want to go from 0 to -100 you have to use a
decreasing function, just as well if you want to go from 100
to 0. Using a min-depth of 100 and a max-depth of 0 and an
increasing function is undefined behaviour.
* tests/Makefile.am:
* tests/test-depth.c: Add a test case for the depth behaviour.
