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, 7 insertions, 3 deletions

diff --git a/Alc/ALu.c b/Alc/ALu.c
index aff87895..55f0c09a 100644
--- a/Alc/ALu.c
+++ b/Alc/ALu.c
@@ -634,10 +634,11 @@ static void CalcNonAttnSourceParams(ALvoice *voice, const struct ALsourceProps *
 
                 /* Get the static HRIR coefficients and delays for this channel. */
                 GetHrtfCoeffs(Device->HrtfHandle,
-                    chans[c].elevation, chans[c].angle, 0.0f, DryGain,
+                    chans[c].elevation, chans[c].angle, 0.0f,
                     voice->Direct.Params[c].Hrtf.Target.Coeffs,
                     voice->Direct.Params[c].Hrtf.Target.Delay
                 );
+                voice->Direct.Params[c].Hrtf.Target.Gain = DryGain;
 
                 /* Normal panning for auxiliary sends. */
                 CalcAngleCoeffs(chans[c].angle, chans[c].elevation, 0.0f, coeffs);
@@ -1104,9 +1105,10 @@ static void CalcAttnSourceParams(ALvoice *voice, const struct ALsourceProps *pro
             spread = asinf(radius / Distance) * 2.0f;
 
         /* Get the HRIR coefficients and delays. */
-        GetHrtfCoeffs(Device->HrtfHandle, ev, az, spread, DryGain,
+        GetHrtfCoeffs(Device->HrtfHandle, ev, az, spread,
                       voice->Direct.Params[0].Hrtf.Target.Coeffs,
                       voice->Direct.Params[0].Hrtf.Target.Delay);
+        voice->Direct.Params[0].Hrtf.Target.Gain = DryGain;
 
         CalcDirectionCoeffs(dir, spread, coeffs);
 
@@ -1502,9 +1504,11 @@ void aluMixData(ALCdevice *device, ALvoid *buffer, ALsizei size)
             state = device->Hrtf;
             for(c = 0;c < device->Dry.NumChannels;c++)
             {
+                typedef ALfloat ALfloat2[2];
                 HrtfMix(device->RealOut.Buffer[lidx], device->RealOut.Buffer[ridx],
                     device->Dry.Buffer[c], state->Offset, state->IrSize,
-                    state->Chan[c].Coeffs, state->Chan[c].Values, SamplesToDo
+                    SAFE_CONST(ALfloat2*,state->Chan[c].Coeffs),
+                    state->Chan[c].Values, SamplesToDo
                 );
             }
             state->Offset += SamplesToDo;