Now FuMa and ACN channel orders are required, as are FuMa, SN3D, and N3D
normalization schemes. An integer query (alcGetIntegerv) is added for the
maximum ambisonic order.
The context state properties are less likely to change compared to the listener
state, and future changes may prefer more infrequent updates to the context
state.
Note that this puts the MetersPerUnit in as a context state, even though it's
handled through the listener functions. Considering the infrequency that it's
updated at (generally set just once for the context's lifetime), it makes more
sense to put it there than with the more frequently updated listener
properties. The aforementioned future changes would also prefer MetersPerUnit
to not be updated unnecessarily.
This improves a stereo (front-left + front-right) sound "image" by generating a
front-center channel signal. Done correctly, it helps reduce the comb effects
and phase errors associated with using only two speakers to simulate center
sounds.
Note that it shouldn't be used if the front-center channel is already included
in the positional audio mix (the dialog effect is okay). In general, it may
actually be better to exclude the front-center channel from the positional
audio mix and use this to generate front-center output.
I say "convert" because it takes the lazy way and essentially just embeds the
wrappers into the backend. It's done this way because I lack the means to check
any changes, even syntactically. This also means the device's ExtraData field
is still needed.
However, this does mean all the backends are now using the new API. Code
related to the old interface can now be removed.
This is just for the output limiter right now, but in the future can be used
for the compressor EFX effect. The parameters are also hardcoded, but can be
made configurable after 1.18.
This reduces the output volume when the mixed samples extend outside of -1,+1,
to prevent excessive clipping. It can reduce the volume by -80dB in 50ms, and
increase it by +80dB in 1s (it will not go below -80dB or above 0dB).
