The inverted atomic flag replaces test_and_set+clear with test_and_clear+set,
essentially inverting the flag status. This makes more logical sense for
flagging dirty state, which is less confusing than flagging clean state. The
one caveat is ATOMIC_FLAG_INIT (or default construction in C++20) initializes
the state to true rather than false.
This uses a bit more memory (each voice needs to hold buffers for the
deinterleaved samples of each channel, instead of just one buffer for the
current channel being mixed on the device), but it will allow for handling
formats that need or prefer their channels decoded together.
This mainly avoids having to allocate ~64-byte structures individually. The
mixing voice still holds the queue as a linked list so as to be container-
agnostic.
Used when upsampling low-order ambisonic signals to higher order. Rather than a
hardcoded 400hz, it ensures a consistent crossover point when an ambdec
configuration is used. It can also allow for an alsoft config option.
Rather than allocating for a full 8 channels for each voice, when the vast
majority will only need 1 or 2. The voice channel data is relatively big since
it needs to hold HRTF coefficients and history, and this will allow increasing
the maximum number of buffer channels without an obscene memory increase.
When starting a voice, the source ID was set before its first update struct was
provided, creating a small window where a listener or effect slot update could
force a voice to update without it having any valid properties to update with.
Supplying the update struct first would create a different race, where the
mixer could see a voice without a source but with an update struct, causing the
update struct to be 'freed' without being applied.
The fix here is to provide the update struct before setting the source ID, and
change the mixer to ignore update structs for voices without a source ID. This
can pseudo-orphan the updates that get set on a voice just as it stops, leaving
the struct unusable until the voice is used again, or the voice gets deleted
which will clear it. But it allows the update struct to stay in place and get
applied once the voice gets a source ID.
