Previously the backend private state was used to either link to an
authority material or provide authoritative program state. The mechanism
seemed overly complex and felt very fragile. I made a recent comment
which added a lot of documentation to make it easier to understand but
still it didn't feel very elegant.
This patch takes a slightly different approach; we now have a
ref-counted ArbfpProgramState object which encapsulates a single ARBfp
program and the backend private state now just has a single member which
is a pointer to one of these arbfp_program_state objects. We no longer
need to cache pointers to our arbfp-authority and so we can get rid of
a lot of awkward code that ensured these pointers were
updated/invalidated at the right times. The program state objects are
not tightly bound to a material so it will also allow us to later
implement a cache mechanism that lets us share state outside a materials
ancestry. This may help to optimize code not following the
recommendations of deriving materials from templates, avoiding one-shot
materials and not repeatedly modifying materials because even if a
material's ancestry doesn't naturally lead us to shareable state we can
fallback to searching for shareable state using central hash tables.
cad5624a2a