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, 6 insertions, 9 deletions

diff --git a/Alc/mixer_defs.h b/Alc/mixer_defs.h
index c1500ed2..62dad9dc 100644
--- a/Alc/mixer_defs.h
+++ b/Alc/mixer_defs.h
@@ -20,17 +20,15 @@ const ALfloat *Resample_cubic32_C(const ALfloat *src, ALuint frac, ALuint increm
 
 /* C mixers */
 void MixHrtf_C(ALfloat (*restrict OutBuffer)[BUFFERSIZE], const ALfloat *data,
-               ALuint Counter, ALuint Offset, ALuint OutPos, const ALuint IrSize,
-               const struct HrtfParams *hrtfparams, struct HrtfState *hrtfstate,
-               ALuint BufferSize);
+               ALuint Offset, const ALuint IrSize, const struct HrtfParams *hrtfparams,
+               struct HrtfState *hrtfstate, ALuint BufferSize);
 void Mix_C(const ALfloat *data, ALuint OutChans, ALfloat (*restrict OutBuffer)[BUFFERSIZE],
                  struct MixGains *Gains, ALuint Counter, ALuint OutPos, ALuint BufferSize);
 
 /* SSE mixers */
 void MixHrtf_SSE(ALfloat (*restrict OutBuffer)[BUFFERSIZE], const ALfloat *data,
-                 ALuint Counter, ALuint Offset, ALuint OutPos, const ALuint IrSize,
-                 const struct HrtfParams *hrtfparams, struct HrtfState *hrtfstate,
-                 ALuint BufferSize);
+                 ALuint Offset, const ALuint IrSize, const struct HrtfParams *hrtfparams,
+                 struct HrtfState *hrtfstate, ALuint BufferSize);
 void Mix_SSE(const ALfloat *data, ALuint OutChans, ALfloat (*restrict OutBuffer)[BUFFERSIZE],
              struct MixGains *Gains, ALuint Counter, ALuint OutPos, ALuint BufferSize);
 
@@ -56,9 +54,8 @@ const ALfloat *Resample_lerp32_SSE41(const ALfloat *src, ALuint frac, ALuint inc
 
 /* Neon mixers */
 void MixHrtf_Neon(ALfloat (*restrict OutBuffer)[BUFFERSIZE], const ALfloat *data,
-                  ALuint Counter, ALuint Offset, ALuint OutPos, const ALuint IrSize,
-                  const struct HrtfParams *hrtfparams, struct HrtfState *hrtfstate,
-                  ALuint BufferSize);
+                  ALuint Offset, const ALuint IrSize, const struct HrtfParams *hrtfparams,
+                  struct HrtfState *hrtfstate, ALuint BufferSize);
 void Mix_Neon(const ALfloat *data, ALuint OutChans, ALfloat (*restrict OutBuffer)[BUFFERSIZE],
               struct MixGains *Gains, ALuint Counter, ALuint OutPos, ALuint BufferSize);