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, 1 insertions, 36 deletions

diff --git a/Alc/mixer_neon.c b/Alc/mixer_neon.c
index 727c5c55..390a1dd2 100644
--- a/Alc/mixer_neon.c
+++ b/Alc/mixer_neon.c
@@ -190,44 +190,9 @@ const ALfloat *Resample_bsinc32_Neon(const InterpState *state,
 }
 
 
-static inline void ApplyCoeffsStep(ALsizei Offset, ALfloat (*restrict Values)[2],
-                                   const ALsizei IrSize,
-                                   ALfloat (*restrict Coeffs)[2],
-                                   const ALfloat (*restrict CoeffStep)[2],
-                                   ALfloat left, ALfloat right)
-{
-    ALsizei c;
-    float32x4_t leftright4;
-    {
-        float32x2_t leftright2 = vdup_n_f32(0.0);
-        leftright2 = vset_lane_f32(left, leftright2, 0);
-        leftright2 = vset_lane_f32(right, leftright2, 1);
-        leftright4 = vcombine_f32(leftright2, leftright2);
-    }
-    Values = ASSUME_ALIGNED(Values, 16);
-    Coeffs = ASSUME_ALIGNED(Coeffs, 16);
-    CoeffStep = ASSUME_ALIGNED(CoeffStep, 16);
-    for(c = 0;c < IrSize;c += 2)
-    {
-        const ALsizei o0 = (Offset+c)&HRIR_MASK;
-        const ALsizei o1 = (o0+1)&HRIR_MASK;
-        float32x4_t vals = vcombine_f32(vld1_f32((float32_t*)&Values[o0][0]),
-                                        vld1_f32((float32_t*)&Values[o1][0]));
-        float32x4_t coefs = vld1q_f32((float32_t*)&Coeffs[c][0]);
-        float32x4_t deltas = vld1q_f32(&CoeffStep[c][0]);
-
-        vals = vmlaq_f32(vals, coefs, leftright4);
-        coefs = vaddq_f32(coefs, deltas);
-
-        vst1_f32((float32_t*)&Values[o0][0], vget_low_f32(vals));
-        vst1_f32((float32_t*)&Values[o1][0], vget_high_f32(vals));
-        vst1q_f32(&Coeffs[c][0], coefs);
-    }
-}
-
 static inline void ApplyCoeffs(ALsizei Offset, ALfloat (*restrict Values)[2],
                                const ALsizei IrSize,
-                               ALfloat (*restrict Coeffs)[2],
+                               const ALfloat (*restrict Coeffs)[2],
                                ALfloat left, ALfloat right)
 {
     ALsizei c;