From 529f387695d10368aca3460baa428ee90eea8332 Mon Sep 17 00:00:00 2001
From: Chris Robinson <chris.kcat@gmail.com>
Date: Wed, 29 Aug 2018 01:45:27 -0700
Subject: Use a separate method to warp the azimuth for plain stereo output

---
 Alc/ALu.c              | 27 ++++++++++++++-------------
 Alc/panning.c          |  9 +--------
 OpenAL32/Include/alu.h | 16 ++++++++++------
 3 files changed, 25 insertions(+), 27 deletions(-)

diff --git a/Alc/ALu.c b/Alc/ALu.c
index dc24755d..d033c0c4 100644
--- a/Alc/ALu.c
+++ b/Alc/ALu.c
@@ -648,10 +648,12 @@ static void CalcPanningAndFilters(ALvoice *voice, const ALfloat Azi, const ALflo
                 voice->Flags |= VOICE_HAS_NFC;
             }
 
-            if(Device->Render_Mode == StereoPair)
-                CalcAnglePairwiseCoeffs(Azi, Elev, Spread, coeffs);
-            else
-                CalcAngleCoeffs(Azi, Elev, Spread, coeffs);
+            /* A scalar of 3 for plain stereo results in +/-30 degrees being
+             * moved to +/-90 degrees for direct right and left speaker
+             * responses.
+             */
+            CalcAngleCoeffs((Device->Render_Mode==StereoPair) ? ScaleAzimuthFront(Azi, 3.0f) : Azi,
+                            Elev, Spread, coeffs);
 
             /* NOTE: W needs to be scaled by sqrt(2) due to FuMa normalization. */
             ComputeDryPanGains(&Device->Dry, coeffs, DryGain*1.414213562f,
@@ -895,10 +897,8 @@ static void CalcPanningAndFilters(ALvoice *voice, const ALfloat Azi, const ALflo
             /* Calculate the directional coefficients once, which apply to all
              * input channels.
              */
-            if(Device->Render_Mode == StereoPair)
-                CalcAnglePairwiseCoeffs(Azi, Elev, Spread, coeffs);
-            else
-                CalcAngleCoeffs(Azi, Elev, Spread, coeffs);
+            CalcAngleCoeffs((Device->Render_Mode==StereoPair) ? ScaleAzimuthFront(Azi, 3.0f) : Azi,
+                            Elev, Spread, coeffs);
 
             for(c = 0;c < num_channels;c++)
             {
@@ -970,14 +970,15 @@ static void CalcPanningAndFilters(ALvoice *voice, const ALfloat Azi, const ALflo
                     continue;
                 }
 
-                if(Device->Render_Mode == StereoPair)
-                    CalcAnglePairwiseCoeffs(chans[c].angle, chans[c].elevation, Spread, coeffs);
-                else
-                    CalcAngleCoeffs(chans[c].angle, chans[c].elevation, Spread, coeffs);
+                CalcAngleCoeffs(
+                    (Device->Render_Mode==StereoPair) ? ScaleAzimuthFront(chans[c].angle, 3.0f)
+                                                      : chans[c].angle,
+                    chans[c].elevation, Spread, coeffs
+                );
+
                 ComputeDryPanGains(&Device->Dry,
                     coeffs, DryGain, voice->Direct.Params[c].Gains.Target
                 );
-
                 for(i = 0;i < NumSends;i++)
                 {
                     const ALeffectslot *Slot = SendSlots[i];
diff --git a/Alc/panning.c b/Alc/panning.c
index 51d65a24..d114295b 100644
--- a/Alc/panning.c
+++ b/Alc/panning.c
@@ -40,6 +40,7 @@
 
 extern inline void CalcDirectionCoeffs(const ALfloat dir[3], ALfloat spread, ALfloat coeffs[MAX_AMBI_COEFFS]);
 extern inline void CalcAngleCoeffs(ALfloat azimuth, ALfloat elevation, ALfloat spread, ALfloat coeffs[MAX_AMBI_COEFFS]);
+extern inline float ScaleAzimuthFront(float azimuth, float scale);
 extern inline void ComputeDryPanGains(const DryMixParams *dry, const ALfloat coeffs[MAX_AMBI_COEFFS], ALfloat ingain, ALfloat gains[MAX_OUTPUT_CHANNELS]);
 extern inline void ComputeFirstOrderGains(const BFMixParams *foa, const ALfloat mtx[4], ALfloat ingain, ALfloat gains[MAX_OUTPUT_CHANNELS]);
 
@@ -150,14 +151,6 @@ void CalcAmbiCoeffs(const ALfloat y, const ALfloat z, const ALfloat x, const ALf
     }
 }
 
-void CalcAnglePairwiseCoeffs(ALfloat azimuth, ALfloat elevation, ALfloat spread, ALfloat coeffs[MAX_AMBI_COEFFS])
-{
-    ALfloat sign = (azimuth < 0.0f) ? -1.0f : 1.0f;
-    if(!(fabsf(azimuth) > F_PI_2))
-        azimuth = minf(fabsf(azimuth) * F_PI_2 / (F_PI/6.0f), F_PI_2) * sign;
-    CalcAngleCoeffs(azimuth, elevation, spread, coeffs);
-}
-
 
 void ComputePanningGainsMC(const ChannelConfig *chancoeffs, ALsizei numchans, ALsizei numcoeffs, const ALfloat coeffs[MAX_AMBI_COEFFS], ALfloat ingain, ALfloat gains[MAX_OUTPUT_CHANNELS])
 {
diff --git a/OpenAL32/Include/alu.h b/OpenAL32/Include/alu.h
index c09caa65..ed318ada 100644
--- a/OpenAL32/Include/alu.h
+++ b/OpenAL32/Include/alu.h
@@ -477,14 +477,18 @@ inline void CalcAngleCoeffs(ALfloat azimuth, ALfloat elevation, ALfloat spread,
 }
 
 /**
- * CalcAnglePairwiseCoeffs
+ * ScaleAzimuthFront
  *
- * Calculates ambisonic coefficients based on azimuth and elevation. The
- * azimuth and elevation parameters are in radians, going right and up
- * respectively. This pairwise variant warps the result such that +30 azimuth
- * is full right, and -30 azimuth is full left.
+ * Scales the given azimuth toward the side (+/- pi/2 radians) for positions in
+ * front.
  */
-void CalcAnglePairwiseCoeffs(ALfloat azimuth, ALfloat elevation, ALfloat spread, ALfloat coeffs[MAX_AMBI_COEFFS]);
+inline float ScaleAzimuthFront(float azimuth, float scale)
+{
+    ALfloat sign = (azimuth < 0.0f) ? -1.0f : 1.0f;
+    if(!(fabsf(azimuth) > F_PI_2))
+        return minf(fabsf(azimuth) * scale, F_PI_2) * sign;
+    return azimuth;
+}
 
 
 void ComputePanningGainsMC(const ChannelConfig *chancoeffs, ALsizei numchans, ALsizei numcoeffs, const ALfloat coeffs[MAX_AMBI_COEFFS], ALfloat ingain, ALfloat gains[MAX_OUTPUT_CHANNELS]);
-- 
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