Rework HRTF coefficient fading

This improves fading between HRIRs as sources pan around. In particular, it
improves the issue with individual coefficients having various rounding errors
in the stepping values, as well as issues with interpolating delay values.

It does this by doing two mixing passes for each source. First using the last
coefficients that fade to silence, and then again using the new coefficients
that fade from silence. When added together, it creates a linear fade from one
to the other. Additionally, the gain is applied separately so the individual
coefficients don't step with rounding errors. Although this does increase CPU
cost since it's doing two mixes per source, each mix is a bit cheaper now since
the stepping is simplified to a single gain value, and the overall quality is
improved.

1 files changed, 9 insertions, 9 deletions

diff --git a/Alc/mixer_defs.h b/Alc/mixer_defs.h
index b76c9aee..d4a49b53 100644
--- a/Alc/mixer_defs.h
+++ b/Alc/mixer_defs.h
@@ -21,12 +21,12 @@ const ALfloat *Resample_bsinc32_C(const InterpState *state, const ALfloat *restr
 
 /* C mixers */
 void MixHrtf_C(ALfloat *restrict LeftOut, ALfloat *restrict RightOut,
-               const ALfloat *data, ALsizei Counter, ALsizei Offset, ALsizei OutPos,
-               const ALsizei IrSize, const struct MixHrtfParams *hrtfparams,
+               const ALfloat *data, ALsizei Offset, ALsizei OutPos,
+               const ALsizei IrSize, struct MixHrtfParams *hrtfparams,
                struct HrtfState *hrtfstate, ALsizei BufferSize);
 void MixDirectHrtf_C(ALfloat *restrict LeftOut, ALfloat *restrict RightOut,
                      const ALfloat *data, ALsizei Offset, const ALsizei IrSize,
-                     ALfloat (*restrict Coeffs)[2], ALfloat (*restrict Values)[2],
+                     const ALfloat (*restrict Coeffs)[2], ALfloat (*restrict Values)[2],
                      ALsizei BufferSize);
 void Mix_C(const ALfloat *data, ALsizei OutChans, ALfloat (*restrict OutBuffer)[BUFFERSIZE],
            ALfloat *CurrentGains, const ALfloat *TargetGains, ALsizei Counter, ALsizei OutPos,
@@ -37,12 +37,12 @@ void MixRow_C(ALfloat *OutBuffer, const ALfloat *Gains,
 
 /* SSE mixers */
 void MixHrtf_SSE(ALfloat *restrict LeftOut, ALfloat *restrict RightOut,
-                 const ALfloat *data, ALsizei Counter, ALsizei Offset, ALsizei OutPos,
-                 const ALsizei IrSize, const struct MixHrtfParams *hrtfparams,
+                 const ALfloat *data, ALsizei Offset, ALsizei OutPos,
+                 const ALsizei IrSize, struct MixHrtfParams *hrtfparams,
                  struct HrtfState *hrtfstate, ALsizei BufferSize);
 void MixDirectHrtf_SSE(ALfloat *restrict LeftOut, ALfloat *restrict RightOut,
                        const ALfloat *data, ALsizei Offset, const ALsizei IrSize,
-                       ALfloat (*restrict Coeffs)[2], ALfloat (*restrict Values)[2],
+                       const ALfloat (*restrict Coeffs)[2], ALfloat (*restrict Values)[2],
                        ALsizei BufferSize);
 void Mix_SSE(const ALfloat *data, ALsizei OutChans, ALfloat (*restrict OutBuffer)[BUFFERSIZE],
              ALfloat *CurrentGains, const ALfloat *TargetGains, ALsizei Counter, ALsizei OutPos,
@@ -86,12 +86,12 @@ const ALfloat *Resample_bsinc32_SSE(const InterpState *state, const ALfloat *res
 
 /* Neon mixers */
 void MixHrtf_Neon(ALfloat *restrict LeftOut, ALfloat *restrict RightOut,
-                  const ALfloat *data, ALsizei Counter, ALsizei Offset, ALsizei OutPos,
-                  const ALsizei IrSize, const struct MixHrtfParams *hrtfparams,
+                  const ALfloat *data, ALsizei Offset, ALsizei OutPos,
+                  const ALsizei IrSize, struct MixHrtfParams *hrtfparams,
                   struct HrtfState *hrtfstate, ALsizei BufferSize);
 void MixDirectHrtf_Neon(ALfloat *restrict LeftOut, ALfloat *restrict RightOut,
                         const ALfloat *data, ALsizei Offset, const ALsizei IrSize,
-                        ALfloat (*restrict Coeffs)[2], ALfloat (*restrict Values)[2],
+                        const ALfloat (*restrict Coeffs)[2], ALfloat (*restrict Values)[2],
                         ALsizei BufferSize);
 void Mix_Neon(const ALfloat *data, ALsizei OutChans, ALfloat (*restrict OutBuffer)[BUFFERSIZE],
               ALfloat *CurrentGains, const ALfloat *TargetGains, ALsizei Counter, ALsizei OutPos,