Similar to the listener, separate containers are provided atomically for the
mixer thread to apply updates without needing to block, and a free-list is used
to reuse container objects.
A couple things to note. First, the lock is still used when the effect state's
deviceUpdate method is called to prevent asynchronous calls to reset the device
from interfering. This can be fixed by using the list lock in ALc.c instead.
Secondly, old effect states aren't immediately deleted when the effect type
changes (the actual type, not just its properties). This is because the mixer
thread is intended to be real-time safe, and so can't be freeing anything. They
are cleared away when updates reuse the container they were kept in, and they
don't incur any extra processing cost, but there may be cases where the memory
is kept around until the effect slot is deleted.
The real FrontCenter output is used if it exists, and if it doesn't, it's
unlikely the dry buffer will have it (and even if it does, it won't be any
better than panning).
Instead of looping over all the coefficients for each channel with multiplies,
when we know only one will have a non-0 factor for ambisonic mixing buffers,
just index the one with a non-0 factor.
This is less than ideal, but matching each reverb line to a speaker with
surround sound output is way too loud without the ambient volume scaling
offered by the "direct" panning.
This uses a virtual B-Format buffer for mixing, and then uses a dual-band
decoder for improved positional quality. This currently only works with first-
order output since first-order input (from the AL_EXT_BFROMAT extension) would
not sound correct when fed through a second- or third-order decoder.
This also does not currently implement near-field compensation since near-field
rendering effects are not implemented.
This is pretty hacky. Since HRTF normally renders to B-Format with two "extra"
channels for the real stereo output, the panning interpolates between a panned
reverb channel on B-Format, and two non-panned reverb channels on stereo
output, given the panning vector length.
HRTF and B-Format output still need to use virtual panning directions, but the
reverb works better when it outputs directly to an output channel. Ambient and
directional panning is used to properly mask and attenuate each output channel.
Note that currently the "direct panning" output is quieter than it should be.
Work is underway to attenuate the early reflections and late reverb better.
