From a1d4847d078f4f807f5697f299eea834797f4287 Mon Sep 17 00:00:00 2001
From: Chris Robinson <chris.kcat@gmail.com>
Date: Mon, 9 Feb 2015 15:59:29 -0800
Subject: Use B-Format for HRTF's virtual output format

This adds the ability to directly decode B-Format with HRTF, though only first-
order (WXYZ) for now. Second- and third-order would be easilly doable, however
we'd need to be able to up-mix first-order content (from the BFORMAT2D and
BFORMAT3D buffer formats) since it would be inappropriate to decode lower-order
content with a higher-order decoder.
---
 Alc/hrtf.c | 84 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 83 insertions(+), 1 deletion(-)

(limited to 'Alc/hrtf.c')

diff --git a/Alc/hrtf.c b/Alc/hrtf.c
index 54e16cc7..98bcefc2 100644
--- a/Alc/hrtf.c
+++ b/Alc/hrtf.c
@@ -82,7 +82,7 @@ static void CalcEvIndices(ALuint evcount, ALfloat ev, ALuint *evidx, ALfloat *ev
  */
 static void CalcAzIndices(ALuint azcount, ALfloat az, ALuint *azidx, ALfloat *azmu)
 {
-    az = (F_2PI + az) * azcount / (F_2PI);
+    az = (F_2PI + az) * azcount / F_2PI;
     azidx[0] = fastf2u(az) % azcount;
     azidx[1] = (azidx[0] + 1) % azcount;
     *azmu = az - floorf(az);
@@ -312,6 +312,88 @@ ALuint GetMovingHrtfCoeffs(const struct Hrtf *Hrtf, ALfloat elevation, ALfloat a
 }
 
 
+/* Calculates HRTF coefficients for a B-Format channel (first order only). */
+void GetBFormatHrtfCoeffs(const struct Hrtf *Hrtf, const ALfloat ambi_coeffs[4], ALfloat (*coeffs)[2], ALuint *delays)
+{
+    ALuint elev_idx, azi_idx;
+    ALfloat scale;
+    ALuint i;
+
+    for(i = 0;i < Hrtf->irSize;i++)
+    {
+        coeffs[i][0] = 0.0f;
+        coeffs[i][1] = 0.0f;
+    }
+    delays[0] = 0;
+    delays[1] = 0;
+
+    /* NOTE: HRTF coefficients are generated by combining all the HRIRs in the
+     * dataset, with each entry scaled according to how much it contributes to
+     * the given B-Format channel based on its direction (including negative
+     * contributions!).
+     */
+    scale = 0.0f;
+    for(elev_idx = 0;elev_idx < Hrtf->evCount;elev_idx++)
+    {
+        ALfloat elev = (ALfloat)elev_idx/(ALfloat)(Hrtf->evCount-1)*F_PI - F_PI_2;
+        ALuint evoffset = Hrtf->evOffset[elev_idx];
+        ALuint azcount = Hrtf->azCount[elev_idx];
+
+        scale += (ALfloat)azcount;
+
+        for(azi_idx = 0;azi_idx < azcount;azi_idx++)
+        {
+            ALuint lidx, ridx;
+            ALfloat az;
+            ALfloat x, y, z;
+            ALfloat gain;
+
+            lidx = evoffset + azi_idx;
+            ridx = evoffset + ((azcount-azi_idx) % azcount);
+
+            /* NOTE: Always include the total delay average since the channels
+             * need to have matching delays. */
+            delays[0] += Hrtf->delays[lidx];
+            delays[1] += Hrtf->delays[ridx];
+
+            az = (ALfloat)azi_idx / (ALfloat)azcount * F_2PI;
+            if(az > F_PI) az -= F_2PI;
+
+            x =  cosf(az) * cosf(elev);
+            y = -sinf(az) * cosf(elev);
+            z =  sinf(elev);
+
+            gain = 0.0f;
+            gain += ambi_coeffs[0]*0.7071f; /* sqrt(1.0 / 2.0) */
+            gain += ambi_coeffs[1]*x; /* X */
+            gain += ambi_coeffs[2]*y; /* Y */
+            gain += ambi_coeffs[3]*z; /* Z */
+
+            if(!(fabsf(gain) > GAIN_SILENCE_THRESHOLD))
+                continue;
+
+            lidx *= Hrtf->irSize;
+            ridx *= Hrtf->irSize;
+            for(i = 0;i < Hrtf->irSize;i++)
+            {
+                coeffs[i][0] += Hrtf->coeffs[lidx + i]*(1.0f/32767.0f) * gain;
+                coeffs[i][1] += Hrtf->coeffs[ridx + i]*(1.0f/32767.0f) * gain;
+            }
+        }
+    }
+
+    scale = 1.0f/scale;
+
+    delays[0] = minu((ALuint)((ALfloat)delays[0] * scale), HRTF_HISTORY_LENGTH-1)<<HRTFDELAY_BITS;
+    delays[1] = minu((ALuint)((ALfloat)delays[1] * scale), HRTF_HISTORY_LENGTH-1)<<HRTFDELAY_BITS;
+    for(i = 0;i < Hrtf->irSize;i++)
+    {
+        coeffs[i][0] *= scale;
+        coeffs[i][1] *= scale;
+    }
+}
+
+
 static struct Hrtf *LoadHrtf00(FILE *f, ALuint deviceRate)
 {
     const ALubyte maxDelay = HRTF_HISTORY_LENGTH-1;
-- 
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