Use a different method for HRTF mixing

This new method mixes sources normally into a 14-channel buffer with the
channels placed all around the listener. HRTF is then applied to the channels
given their positions and written to a 2-channel buffer, which gets written out
to the device.

This method has the benefit that HRTF processing becomes more scalable. The
costly HRTF filters are applied to the 14-channel buffer after the mix is done,
turning it into a post-process with a fixed overhead. Mixing sources is done
with normal non-HRTF methods, so increasing the number of playing sources only
incurs normal mixing costs.

Another benefit is that it improves B-Format playback since the soundfield gets
mixed into speakers covering all three dimensions, which then get filtered
based on their locations.

The main downside to this is that the spatial resolution of the HRTF dataset
does not play a big role anymore. However, the hope is that with ambisonics-
based panning, the perceptual position of panned sounds will still be good. It
is also an option to increase the number of virtual channels for systems that
can handle it, or maybe even decrease it for weaker systems.

1 files changed, 1 insertions, 3 deletions

diff --git a/Alc/hrtf.h b/Alc/hrtf.h
index 938bf552..48636344 100644
--- a/Alc/hrtf.h
+++ b/Alc/hrtf.h
@@ -21,8 +21,6 @@ ALCboolean FindHrtfFormat(enum DevFmtChannels *chans, ALCuint *srate);
 void FreeHrtfs(void);
 
 ALuint GetHrtfIrSize(const struct Hrtf *Hrtf);
-ALfloat CalcHrtfDelta(ALfloat oldGain, ALfloat newGain, const ALfloat olddir[3], const ALfloat newdir[3]);
-void GetLerpedHrtfCoeffs(const struct Hrtf *Hrtf, ALfloat elevation, ALfloat azimuth, ALfloat dirfact, ALfloat gain, ALfloat (*coeffs)[2], ALuint *delays);
-ALuint GetMovingHrtfCoeffs(const struct Hrtf *Hrtf, ALfloat elevation, ALfloat azimuth, ALfloat dirfact, ALfloat gain, ALfloat delta, ALint counter, ALfloat (*coeffs)[2], ALuint *delays, ALfloat (*coeffStep)[2], ALint *delayStep);
+void GetLerpedHrtfCoeffs(const struct Hrtf *Hrtf, ALfloat elevation, ALfloat azimuth, ALfloat (*coeffs)[2], ALuint *delays);
 
 #endif /* ALC_HRTF_H */