Partially revert "Use a different method for HRTF mixing"

The sound localization with virtual channel mixing was just too poor, so while
it's more costly to do per-source HRTF mixing, it's unavoidable if you want
good localization.

This is only partially reverted because having the virtual channel is still
beneficial, particularly with B-Format rendering and effect mixing which
otherwise skip HRTF processing. As before, the number of virtual channels can
potentially be customized, specifying more or less channels depending on the
system's needs.

1 files changed, 40 insertions, 8 deletions

diff --git a/Alc/mixer_inc.c b/Alc/mixer_inc.c
index 46ccec7d..b4635b43 100644
--- a/Alc/mixer_inc.c
+++ b/Alc/mixer_inc.c
@@ -14,6 +14,11 @@
 #define MixHrtf MERGE(MixHrtf_,SUFFIX)
 
 
+static inline void ApplyCoeffsStep(ALuint Offset, ALfloat (*restrict Values)[2],
+                                   const ALuint irSize,
+                                   ALfloat (*restrict Coeffs)[2],
+                                   const ALfloat (*restrict CoeffStep)[2],
+                                   ALfloat left, ALfloat right);
 static inline void ApplyCoeffs(ALuint Offset, ALfloat (*restrict Values)[2],
                                const ALuint irSize,
                                ALfloat (*restrict Coeffs)[2],
@@ -21,7 +26,7 @@ static inline void ApplyCoeffs(ALuint Offset, ALfloat (*restrict Values)[2],
 
 
 void MixHrtf(ALfloat (*restrict OutBuffer)[BUFFERSIZE], const ALfloat *data,
-             ALuint Offset, const ALuint IrSize,
+             ALuint Counter, ALuint Offset, ALuint OutPos, const ALuint IrSize,
              const HrtfParams *hrtfparams, HrtfState *hrtfstate, ALuint BufferSize)
 {
     alignas(16) ALfloat Coeffs[HRIR_LENGTH][2];
@@ -32,13 +37,39 @@ void MixHrtf(ALfloat (*restrict OutBuffer)[BUFFERSIZE], const ALfloat *data,
 
     for(c = 0;c < IrSize;c++)
     {
-        Coeffs[c][0] = hrtfparams->Coeffs[c][0];
-        Coeffs[c][1] = hrtfparams->Coeffs[c][1];
+        Coeffs[c][0] = hrtfparams->Coeffs[c][0] - (hrtfparams->CoeffStep[c][0]*Counter);
+        Coeffs[c][1] = hrtfparams->Coeffs[c][1] - (hrtfparams->CoeffStep[c][1]*Counter);
     }
-    Delay[0] = hrtfparams->Delay[0];
-    Delay[1] = hrtfparams->Delay[1];
+    Delay[0] = hrtfparams->Delay[0] - (hrtfparams->DelayStep[0]*Counter);
+    Delay[1] = hrtfparams->Delay[1] - (hrtfparams->DelayStep[1]*Counter);
 
-    for(pos = 0;pos < BufferSize;pos++)
+    pos = 0;
+    for(;pos < BufferSize && pos < Counter;pos++)
+    {
+        hrtfstate->History[Offset&HRTF_HISTORY_MASK] = data[pos];
+        left  = lerp(hrtfstate->History[(Offset-(Delay[0]>>HRTFDELAY_BITS))&HRTF_HISTORY_MASK],
+                     hrtfstate->History[(Offset-(Delay[0]>>HRTFDELAY_BITS)-1)&HRTF_HISTORY_MASK],
+                     (Delay[0]&HRTFDELAY_MASK)*(1.0f/HRTFDELAY_FRACONE));
+        right = lerp(hrtfstate->History[(Offset-(Delay[1]>>HRTFDELAY_BITS))&HRTF_HISTORY_MASK],
+                     hrtfstate->History[(Offset-(Delay[1]>>HRTFDELAY_BITS)-1)&HRTF_HISTORY_MASK],
+                     (Delay[1]&HRTFDELAY_MASK)*(1.0f/HRTFDELAY_FRACONE));
+
+        Delay[0] += hrtfparams->DelayStep[0];
+        Delay[1] += hrtfparams->DelayStep[1];
+
+        hrtfstate->Values[(Offset+IrSize)&HRIR_MASK][0] = 0.0f;
+        hrtfstate->Values[(Offset+IrSize)&HRIR_MASK][1] = 0.0f;
+        Offset++;
+
+        ApplyCoeffsStep(Offset, hrtfstate->Values, IrSize, Coeffs, hrtfparams->CoeffStep, left, right);
+        OutBuffer[0][OutPos] += hrtfstate->Values[Offset&HRIR_MASK][0];
+        OutBuffer[1][OutPos] += hrtfstate->Values[Offset&HRIR_MASK][1];
+        OutPos++;
+    }
+
+    Delay[0] >>= HRTFDELAY_BITS;
+    Delay[1] >>= HRTFDELAY_BITS;
+    for(;pos < BufferSize;pos++)
     {
         hrtfstate->History[Offset&HRTF_HISTORY_MASK] = data[pos];
         left = hrtfstate->History[(Offset-Delay[0])&HRTF_HISTORY_MASK];
@@ -49,8 +80,9 @@ void MixHrtf(ALfloat (*restrict OutBuffer)[BUFFERSIZE], const ALfloat *data,
         Offset++;
 
         ApplyCoeffs(Offset, hrtfstate->Values, IrSize, Coeffs, left, right);
-        OutBuffer[0][pos] += hrtfstate->Values[Offset&HRIR_MASK][0];
-        OutBuffer[1][pos] += hrtfstate->Values[Offset&HRIR_MASK][1];
+        OutBuffer[0][OutPos] += hrtfstate->Values[Offset&HRIR_MASK][0];
+        OutBuffer[1][OutPos] += hrtfstate->Values[Offset&HRIR_MASK][1];
+        OutPos++;
     }
 }