This is an extremely extensive patch as it hits every cvar, and every
usage of the cvars. Cvars no longer store the value they control,
instead, they use a cexpr value object to reference the value and
specify the value's type (currently, a null type is used for strings).
Non-string cvars are passed through cexpr, allowing expressions in the
cvars' settings. Also, cvars have returned to an enhanced version of the
original (id quake) registration scheme.
As a minor benefit, relevant code having direct access to the
cvar-controlled variables is probably a slight optimization as it
removed a pointer dereference, and the variables can be located for data
locality.
The static cvar descriptors are made private as an additional safety
layer, though there's nothing stopping external modification via
Cvar_FindVar (which is needed for adding listeners).
While not used yet (partly due to working out the design), cvars can
have a validation function.
Registering a cvar allows a primary listener (and its data) to be
specified: it will always be called first when the cvar is modified. The
combination of proper listeners and direct access to the controlled
variable greatly simplifies the more complex cvar interactions as much
less null checking is required, and there's no need for one cvar's
callback to call another's.
nq-x11 is known to work at least well enough for the demos. More testing
will come.
Surprisingly, only two, but they were caught by the different value
fields being used, thus the cvar was checked in multiple places. I
imagine that's not really all that common, so there may be some
inconsistencies between default value and use.
Again, gl/vulkan not working yet (on the assumption that sw would be
trickier).
Fisheye overrides water warp because updating the projection map every
frame is far too expensive.
I've added a post-process pass to the interface in order to hide the
implementation details, but I'm not sure I'm happy about how the
multi-pass rendering for cube maps is handled (or having the frame
buffers as exposed as they are), but mainly because Vulkan will make
implementation interesting.
