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 mixes to a 4-channel first-order ambisonics buffer. With ACN ordering and
N3D scaling, this makes it easy to remain compatible with effects that only
care about mono input since channel 0 is an unattenuated mono signal.
This helps the stability of transforms to local space for sources that are at
or near the listener. With a single-precision matrix, even FLT_EPSILON might
not be enough to detect matching positions.
The extension's not going anywhere, and it can't do anything fluidsynth can't.
The code maintenance and bloat is not worth keeping around, and ideally the AL
API would be able to facilitate MIDI-like behavior anyway (envelopes, start-at-
time, etc).
Note that it still uses FuMa scalings internally. Coefficients loaded from
config files specify if they're FuMa (in both ordering and scaling) or N3D,
and will get reordered or rescaled as needed.
This basically acts as if the app created a new context with the specified
attributes (causing the device to reset with new parameters), then immediately
delete it. Existing contexts remain undisturbed, except for a temporary pause
while the device output is reconfigured.
DISABLED - Generic disabled status
ENABLED - Generic enabled status
DENIED - Not allowed (user has configured HRTF to be off)
REQUIRED - Forced (user has forced HRTF to be used)
HEADPHONES_DETECTED - Enabled because headphones were detected
UNSUPPORTED_FORMAT - Device format is not compatible with available filters
This method is intended to help development by easily testing the quality of
the B-Format encode and B-Format-to-HRTF decode. When used with HRTF, all
sources are renderer using the virtual B-Format output, rather than just
B-Format sources.
Despite the CPU cost savings (only four channels need to be filtered with HRTF,
while sources all render normally), the spatial acuity offered by the B-Format
output is pretty poor since it's only first-order ambisonics, so "full" HRTF
rendering is definitely preferred.
It's /possible/ for some systems to be edge cases that prefer the CPU cost
savings provided by basic over the sharper localization provided by full, and
you do still get 3D positional cues, but this is unlikely to be an actual use-
case in practice.
