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, 104 insertions, 2 deletions

diff --git a/Alc/ALu.c b/Alc/ALu.c
index f7408da0..c4292833 100644
--- a/Alc/ALu.c
+++ b/Alc/ALu.c
@@ -527,6 +527,39 @@ ALvoid CalcNonAttnSourceParams(ALvoice *voice, const ALsource *ALSource, const A
 
         voice->IsHrtf = AL_FALSE;
     }
+    else if(Device->Hrtf)
+    {
+        voice->Direct.OutBuffer = &voice->Direct.OutBuffer[voice->Direct.OutChannels];
+        voice->Direct.OutChannels = 2;
+        for(c = 0;c < num_channels;c++)
+        {
+            if(chans[c].channel == LFE)
+            {
+                /* Skip LFE */
+                voice->Direct.Hrtf.Params[c].Delay[0] = 0;
+                voice->Direct.Hrtf.Params[c].Delay[1] = 0;
+                for(i = 0;i < HRIR_LENGTH;i++)
+                {
+                    voice->Direct.Hrtf.Params[c].Coeffs[i][0] = 0.0f;
+                    voice->Direct.Hrtf.Params[c].Coeffs[i][1] = 0.0f;
+                }
+            }
+            else
+            {
+                /* Get the static HRIR coefficients and delays for this
+                 * channel. */
+                GetLerpedHrtfCoeffs(Device->Hrtf,
+                                    chans[c].elevation, chans[c].angle, 1.0f, DryGain,
+                                    voice->Direct.Hrtf.Params[c].Coeffs,
+                                    voice->Direct.Hrtf.Params[c].Delay);
+            }
+        }
+        voice->Direct.Counter = 0;
+        voice->Direct.Moving  = AL_TRUE;
+        voice->Direct.Hrtf.IrSize = GetHrtfIrSize(Device->Hrtf);
+
+        voice->IsHrtf = AL_TRUE;
+    }
     else
     {
         for(c = 0;c < num_channels;c++)
@@ -934,6 +967,73 @@ ALvoid CalcSourceParams(ALvoice *voice, const ALsource *ALSource, const ALCconte
         BufferListItem = BufferListItem->next;
     }
 
+    if(Device->Hrtf)
+    {
+        /* Use a binaural HRTF algorithm for stereo headphone playback */
+        ALfloat delta, ev = 0.0f, az = 0.0f;
+        ALfloat radius = ALSource->Radius;
+        ALfloat dirfact = 1.0f;
+
+        voice->Direct.OutBuffer = &voice->Direct.OutBuffer[voice->Direct.OutChannels];
+        voice->Direct.OutChannels = 2;
+
+        if(Distance > FLT_EPSILON)
+        {
+            ALfloat invlen = 1.0f/Distance;
+            Position[0] *= invlen;
+            Position[1] *= invlen;
+            Position[2] *= invlen;
+
+            /* Calculate elevation and azimuth only when the source is not at
+             * the listener. This prevents +0 and -0 Z from producing
+             * inconsistent panning. Also, clamp Y in case FP precision errors
+             * cause it to land outside of -1..+1. */
+            ev = asinf(clampf(Position[1], -1.0f, 1.0f));
+            az = atan2f(Position[0], -Position[2]*ZScale);
+        }
+        if(radius > Distance)
+            dirfact *= Distance / radius;
+
+        /* Check to see if the HRIR is already moving. */
+        if(voice->Direct.Moving)
+        {
+            /* Calculate the normalized HRTF transition factor (delta). */
+            delta = CalcHrtfDelta(voice->Direct.Hrtf.Gain, DryGain,
+                                  voice->Direct.Hrtf.Dir, Position);
+            /* If the delta is large enough, get the moving HRIR target
+             * coefficients, target delays, steppping values, and counter. */
+            if(delta > 0.001f)
+            {
+                ALuint counter = GetMovingHrtfCoeffs(Device->Hrtf,
+                    ev, az, dirfact, DryGain, delta, voice->Direct.Counter,
+                    voice->Direct.Hrtf.Params[0].Coeffs, voice->Direct.Hrtf.Params[0].Delay,
+                    voice->Direct.Hrtf.Params[0].CoeffStep, voice->Direct.Hrtf.Params[0].DelayStep
+                );
+                voice->Direct.Counter = counter;
+                voice->Direct.Hrtf.Gain = DryGain;
+                voice->Direct.Hrtf.Dir[0] = Position[0];
+                voice->Direct.Hrtf.Dir[1] = Position[1];
+                voice->Direct.Hrtf.Dir[2] = Position[2];
+            }
+        }
+        else
+        {
+            /* Get the initial (static) HRIR coefficients and delays. */
+            GetLerpedHrtfCoeffs(Device->Hrtf, ev, az, dirfact, DryGain,
+                                voice->Direct.Hrtf.Params[0].Coeffs,
+                                voice->Direct.Hrtf.Params[0].Delay);
+            voice->Direct.Counter = 0;
+            voice->Direct.Moving  = AL_TRUE;
+            voice->Direct.Hrtf.Gain = DryGain;
+            voice->Direct.Hrtf.Dir[0] = Position[0];
+            voice->Direct.Hrtf.Dir[1] = Position[1];
+            voice->Direct.Hrtf.Dir[2] = Position[2];
+        }
+        voice->Direct.Hrtf.IrSize = GetHrtfIrSize(Device->Hrtf);
+
+        voice->IsHrtf = AL_TRUE;
+    }
+    else
     {
         MixGains *gains = voice->Direct.Gains[0];
         ALfloat radius = ALSource->Radius;
@@ -1168,8 +1268,10 @@ ALvoid aluMixData(ALCdevice *device, ALvoid *buffer, ALsizei size)
             HrtfMixerFunc HrtfMix = SelectHrtfMixer();
             ALuint irsize = GetHrtfIrSize(device->Hrtf);
             for(c = 0;c < device->NumChannels;c++)
-                HrtfMix(&device->DryBuffer[outchanoffset], device->DryBuffer[c], device->Hrtf_Offset, irsize,
-                        &device->Hrtf_Params[c], &device->Hrtf_State[c], SamplesToDo);
+                HrtfMix(&device->DryBuffer[outchanoffset], device->DryBuffer[c], 0.0f,
+                    device->Hrtf_Offset, 0.0f, irsize, &device->Hrtf_Params[c],
+                    &device->Hrtf_State[c], SamplesToDo
+                );
             device->Hrtf_Offset += SamplesToDo;
         }
         else if(device->Bs2b)