Since 365605cf42, materials and layers are represented in a tree
structure that allows traversing up through parents and iterating down
through children. This re-works the related typedefs and reparenting
code so that they can be shared.
Previously cogl_set_fog would cause a flush of the Cogl journal and
would directly bang the GL state machine to setup fogging. As part of
the ongoing effort to track most state in CoglMaterial to support
renderlists this now adds an indirection so that cogl_set_fog now just
updates ctx->legacy_fog_state. The fogging state then gets enabled as a
legacy override similar to how the old depth testing API is handled.
The commit to split the fragment processing backends out from
cogl-material.c (3e1323a636) broke the GLES 1 and 2 builds the
fix was to guard the code in each backend according to the
COGL_MATERIAL_BACKEND_XYZ defines which are setup in
cogl-material-private.h.
This splits the fragment processing backends (glsl, arbfp and fixed) out
from cogl-material.c into their own cogl-material-{glsl,arbfp,fixed}.c
files in an effort to help and keep cogl-material.c maintainable.
