Alter how panpot/pair-wise panning works

This change allows pair-wise panning to mostly go through the normal ambisonic
panning methods, with one special-case. First, a term is added to the stereo
decoder matrix's X coefficient so that a centered sound is reduced by -3dB on
each output channel. Panning in front creates a similar gain response to the
typical
L = sqrt(1-pan)
R = sqrt(pan)
for pan = [0,1]. Panning behind the listener can reduce (up to) an additional
-10dB, creating a audible difference between front and back sounds as if
simulating head obstruction.

Secondly, as a special-case, the source positions are warped when calculating
the ambisonic coefficients so that full left panning is reached at -30 degrees
and full right at +30 degrees. This is to retain the expected 60-degree stereo
width. This warping does not apply to B-Format buffer input, although it
otherwise has the same gain responses.

2 files changed, 22 insertions, 32 deletions

diff --git a/Alc/ALu.c b/Alc/ALu.c
index bc48dd59..5a5e6fdf 100644
--- a/Alc/ALu.c
+++ b/Alc/ALu.c
@@ -679,23 +679,12 @@ static void CalcNonAttnSourceParams(ALvoice *voice, const struct ALsourceProps *
                 }
 
                 if(Device->Render_Mode == StereoPair)
-                {
-                    /* Clamp X so it remains within 30 degrees of 0 or 180 degree azimuth. */
-                    ALfloat x = sinf(chans[c].angle) * cosf(chans[c].elevation);
-                    coeffs[0] = clampf(-x, -0.5f, 0.5f) + 0.5f;
-                    voice->Direct.Params[c].Gains.Target[0] = sqrtf(coeffs[0]) * DryGain;
-                    voice->Direct.Params[c].Gains.Target[1] = sqrtf(1.0f-coeffs[0]) * DryGain;
-                    for(j = 2;j < MAX_OUTPUT_CHANNELS;j++)
-                        voice->Direct.Params[c].Gains.Target[j] = 0.0f;
-
-                    CalcAngleCoeffs(chans[c].angle, chans[c].elevation, 0.0f, coeffs);
-                }
+                    CalcAnglePairwiseCoeffs(chans[c].angle, chans[c].elevation, 0.0f, coeffs);
                 else
-                {
                     CalcAngleCoeffs(chans[c].angle, chans[c].elevation, 0.0f, coeffs);
-                    ComputePanningGains(Device->Dry, coeffs, DryGain,
-                                        voice->Direct.Params[c].Gains.Target);
-                }
+                ComputePanningGains(Device->Dry,
+                    coeffs, DryGain, voice->Direct.Params[c].Gains.Target
+                );
 
                 for(i = 0;i < NumSends;i++)
                 {
@@ -1173,22 +1162,15 @@ static void CalcAttnSourceParams(ALvoice *voice, const struct ALsourceProps *pro
 
         if(Device->Render_Mode == StereoPair)
         {
-            /* Clamp X so it remains within 30 degrees of 0 or 180 degree azimuth. */
-            ALfloat x = -dir[0] * (0.5f * (cosf(spread*0.5f) + 1.0f));
-            x = clampf(x, -0.5f, 0.5f) + 0.5f;
-            voice->Direct.Params[0].Gains.Target[0] = sqrtf(x) * DryGain;
-            voice->Direct.Params[0].Gains.Target[1] = sqrtf(1.0f-x) * DryGain;
-            for(i = 2;i < MAX_OUTPUT_CHANNELS;i++)
-                voice->Direct.Params[0].Gains.Target[i] = 0.0f;
-
-            CalcDirectionCoeffs(dir, spread, coeffs);
+            ALfloat ev = asinf(clampf(dir[1], -1.0f, 1.0f));
+            ALfloat az = atan2f(dir[0], -dir[2]);
+            CalcAnglePairwiseCoeffs(az, ev, radius, coeffs);
         }
         else
-        {
             CalcDirectionCoeffs(dir, spread, coeffs);
-            ComputePanningGains(Device->Dry, coeffs, DryGain,
-                                voice->Direct.Params[0].Gains.Target);
-        }
+        ComputePanningGains(Device->Dry,
+            coeffs, DryGain, voice->Direct.Params[0].Gains.Target
+        );
 
         for(i = 0;i < NumSends;i++)
         {
diff --git a/Alc/panning.c b/Alc/panning.c
index 72b55792..7b551100 100644
--- a/Alc/panning.c
+++ b/Alc/panning.c
@@ -202,6 +202,14 @@ void CalcAngleCoeffs(ALfloat azimuth, ALfloat elevation, ALfloat spread, ALfloat
     CalcDirectionCoeffs(dir, spread, coeffs);
 }
 
+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 ComputeAmbientGainsMC(const ChannelConfig *chancoeffs, ALsizei numchans, ALfloat ingain, ALfloat gains[MAX_OUTPUT_CHANNELS])
 {
@@ -237,7 +245,7 @@ void ComputePanningGainsMC(const ChannelConfig *chancoeffs, ALsizei numchans, AL
         float gain = 0.0f;
         for(j = 0;j < numcoeffs;j++)
             gain += chancoeffs[i][j]*coeffs[j];
-        gains[i] = gain * ingain;
+        gains[i] = clampf(gain, 0.0f, 1.0f) * ingain;
     }
     for(;i < MAX_OUTPUT_CHANNELS;i++)
         gains[i] = 0.0f;
@@ -262,7 +270,7 @@ void ComputeFirstOrderGainsMC(const ChannelConfig *chancoeffs, ALsizei numchans,
         float gain = 0.0f;
         for(j = 0;j < 4;j++)
             gain += chancoeffs[i][j] * mtx[j];
-        gains[i] = gain * ingain;
+        gains[i] = clampf(gain, 0.0f, 1.0f) * ingain;
     }
     for(;i < MAX_OUTPUT_CHANNELS;i++)
         gains[i] = 0.0f;
@@ -454,8 +462,8 @@ static bool MakeSpeakerMap(ALCdevice *device, const AmbDecConf *conf, ALsizei sp
 static const ChannelMap MonoCfg[1] = {
     { FrontCenter, { 1.0f } },
 }, StereoCfg[2] = {
-    { FrontLeft,   { 5.00000000e-1f,  2.88675135e-1f, 0.0f,  0.00000000e+0f } },
-    { FrontRight,  { 5.00000000e-1f, -2.88675135e-1f, 0.0f,  0.00000000e+0f } },
+    { FrontLeft,   { 5.00000000e-1f,  2.88675135e-1f, 0.0f,  1.19573156e-1f } },
+    { FrontRight,  { 5.00000000e-1f, -2.88675135e-1f, 0.0f,  1.19573156e-1f } },
 }, QuadCfg[4] = {
     { BackLeft,    { 3.53553391e-1f,  2.04124145e-1f, 0.0f, -2.04124145e-1f } },
     { FrontLeft,   { 3.53553391e-1f,  2.04124145e-1f, 0.0f,  2.04124145e-1f } },