Partially revert "Use a different method for HRTF mixing"

The sound localization with virtual channel mixing was just too poor, so while
it's more costly to do per-source HRTF mixing, it's unavoidable if you want
good localization.

This is only partially reverted because having the virtual channel is still
beneficial, particularly with B-Format rendering and effect mixing which
otherwise skip HRTF processing. As before, the number of virtual channels can
potentially be customized, specifying more or less channels depending on the
system's needs.

1 files changed, 204 insertions, 10 deletions

diff --git a/Alc/hrtf.c b/Alc/hrtf.c
index 2e4156a0..1e371fa4 100644
--- a/Alc/hrtf.c
+++ b/Alc/hrtf.c
@@ -58,6 +58,10 @@ struct Hrtf {
 static const ALchar magicMarker00[8] = "MinPHR00";
 static const ALchar magicMarker01[8] = "MinPHR01";
 
+/* First value for pass-through coefficients (remaining are 0), used for omni-
+ * directional sounds. */
+static const ALfloat PassthruCoeff = 32767.0f * 0.707106781187f/*sqrt(0.5)*/;
+
 static struct Hrtf *LoadedHrtfs = NULL;
 
 /* Calculate the elevation indices given the polar elevation in radians.
@@ -84,12 +88,45 @@ static void CalcAzIndices(ALuint azcount, ALfloat az, ALuint *azidx, ALfloat *az
     *azmu = az - floorf(az);
 }
 
+/* Calculates the normalized HRTF transition factor (delta) from the changes
+ * in gain and listener to source angle between updates.  The result is a
+ * normalized delta factor that can be used to calculate moving HRIR stepping
+ * values.
+ */
+ALfloat CalcHrtfDelta(ALfloat oldGain, ALfloat newGain, const ALfloat olddir[3], const ALfloat newdir[3])
+{
+    ALfloat gainChange, angleChange, change;
+
+    // Calculate the normalized dB gain change.
+    newGain = maxf(newGain, 0.0001f);
+    oldGain = maxf(oldGain, 0.0001f);
+    gainChange = fabsf(log10f(newGain / oldGain) / log10f(0.0001f));
+
+    // Calculate the angle change only when there is enough gain to notice it.
+    angleChange = 0.0f;
+    if(gainChange > 0.0001f || newGain > 0.0001f)
+    {
+        // No angle change when the directions are equal or degenerate (when
+        // both have zero length).
+        if(newdir[0] != olddir[0] || newdir[1] != olddir[1] || newdir[2] != olddir[2])
+        {
+            ALfloat dotp = olddir[0]*newdir[0] + olddir[1]*newdir[1] + olddir[2]*newdir[2];
+            angleChange = acosf(clampf(dotp, -1.0f, 1.0f)) / F_PI;
+        }
+    }
+
+    // Use the largest of the two changes for the delta factor, and apply a
+    // significance shaping function to it.
+    change = maxf(angleChange * 25.0f, gainChange) * 2.0f;
+    return minf(change, 1.0f);
+}
+
 /* Calculates static HRIR coefficients and delays for the given polar
  * elevation and azimuth in radians.  Linear interpolation is used to
  * increase the apparent resolution of the HRIR data set.  The coefficients
  * are also normalized and attenuated by the specified gain.
  */
-void GetLerpedHrtfCoeffs(const struct Hrtf *Hrtf, ALfloat elevation, ALfloat azimuth, ALfloat (*coeffs)[2], ALuint *delays)
+void GetLerpedHrtfCoeffs(const struct Hrtf *Hrtf, ALfloat elevation, ALfloat azimuth, ALfloat dirfact, ALfloat gain, ALfloat (*coeffs)[2], ALuint *delays)
 {
     ALuint evidx[2], lidx[4], ridx[4];
     ALfloat mu[3], blend[4];
@@ -121,12 +158,12 @@ void GetLerpedHrtfCoeffs(const struct Hrtf *Hrtf, ALfloat elevation, ALfloat azi
     blend[3] = (     mu[1]) * (     mu[2]);
 
     /* Calculate the HRIR delays using linear interpolation. */
-    delays[0] = fastf2u(Hrtf->delays[lidx[0]]*blend[0] + Hrtf->delays[lidx[1]]*blend[1] +
-                        Hrtf->delays[lidx[2]]*blend[2] + Hrtf->delays[lidx[3]]*blend[3] +
-                        0.5f);
-    delays[1] = fastf2u(Hrtf->delays[ridx[0]]*blend[0] + Hrtf->delays[ridx[1]]*blend[1] +
-                        Hrtf->delays[ridx[2]]*blend[2] + Hrtf->delays[ridx[3]]*blend[3] +
-                        0.5f);
+    delays[0] = fastf2u((Hrtf->delays[lidx[0]]*blend[0] + Hrtf->delays[lidx[1]]*blend[1] +
+                         Hrtf->delays[lidx[2]]*blend[2] + Hrtf->delays[lidx[3]]*blend[3]) *
+                        dirfact + 0.5f) << HRTFDELAY_BITS;
+    delays[1] = fastf2u((Hrtf->delays[ridx[0]]*blend[0] + Hrtf->delays[ridx[1]]*blend[1] +
+                         Hrtf->delays[ridx[2]]*blend[2] + Hrtf->delays[ridx[3]]*blend[3]) *
+                        dirfact + 0.5f) << HRTFDELAY_BITS;
 
     /* Calculate the sample offsets for the HRIR indices. */
     lidx[0] *= Hrtf->irSize;
@@ -138,16 +175,173 @@ void GetLerpedHrtfCoeffs(const struct Hrtf *Hrtf, ALfloat elevation, ALfloat azi
     ridx[2] *= Hrtf->irSize;
     ridx[3] *= Hrtf->irSize;
 
-    for(i = 0;i < Hrtf->irSize;i++)
+    /* Calculate the normalized and attenuated HRIR coefficients using linear
+     * interpolation when there is enough gain to warrant it.  Zero the
+     * coefficients if gain is too low.
+     */
+    if(gain > 0.0001f)
     {
         ALfloat c;
+
+        i = 0;
         c = (Hrtf->coeffs[lidx[0]+i]*blend[0] + Hrtf->coeffs[lidx[1]+i]*blend[1] +
              Hrtf->coeffs[lidx[2]+i]*blend[2] + Hrtf->coeffs[lidx[3]+i]*blend[3]);
-        coeffs[i][0] = c * (1.0f/32767.0f);
+        coeffs[i][0] = lerp(PassthruCoeff, c, dirfact) * gain * (1.0f/32767.0f);
         c = (Hrtf->coeffs[ridx[0]+i]*blend[0] + Hrtf->coeffs[ridx[1]+i]*blend[1] +
              Hrtf->coeffs[ridx[2]+i]*blend[2] + Hrtf->coeffs[ridx[3]+i]*blend[3]);
-        coeffs[i][1] = c * (1.0f/32767.0f);
+        coeffs[i][1] = lerp(PassthruCoeff, c, dirfact) * gain * (1.0f/32767.0f);
+
+        for(i = 1;i < Hrtf->irSize;i++)
+        {
+            c = (Hrtf->coeffs[lidx[0]+i]*blend[0] + Hrtf->coeffs[lidx[1]+i]*blend[1] +
+                 Hrtf->coeffs[lidx[2]+i]*blend[2] + Hrtf->coeffs[lidx[3]+i]*blend[3]);
+            coeffs[i][0] = lerp(0.0f, c, dirfact) * gain * (1.0f/32767.0f);
+            c = (Hrtf->coeffs[ridx[0]+i]*blend[0] + Hrtf->coeffs[ridx[1]+i]*blend[1] +
+                 Hrtf->coeffs[ridx[2]+i]*blend[2] + Hrtf->coeffs[ridx[3]+i]*blend[3]);
+            coeffs[i][1] = lerp(0.0f, c, dirfact) * gain * (1.0f/32767.0f);
+        }
     }
+    else
+    {
+        for(i = 0;i < Hrtf->irSize;i++)
+        {
+            coeffs[i][0] = 0.0f;
+            coeffs[i][1] = 0.0f;
+        }
+    }
+}
+
+/* Calculates the moving HRIR target coefficients, target delays, and
+ * stepping values for the given polar elevation and azimuth in radians.
+ * Linear interpolation is used to increase the apparent resolution of the
+ * HRIR data set.  The coefficients are also normalized and attenuated by the
+ * specified gain.  Stepping resolution and count is determined using the
+ * given delta factor between 0.0 and 1.0.
+ */
+ALuint GetMovingHrtfCoeffs(const struct Hrtf *Hrtf, ALfloat elevation, ALfloat azimuth, ALfloat dirfact, ALfloat gain, ALfloat delta, ALint counter, ALfloat (*coeffs)[2], ALuint *delays, ALfloat (*coeffStep)[2], ALint *delayStep)
+{
+    ALuint evidx[2], lidx[4], ridx[4];
+    ALfloat mu[3], blend[4];
+    ALfloat left, right;
+    ALfloat step;
+    ALuint i;
+
+    /* Claculate elevation indices and interpolation factor. */
+    CalcEvIndices(Hrtf->evCount, elevation, evidx, &mu[2]);
+
+    for(i = 0;i < 2;i++)
+    {
+        ALuint azcount = Hrtf->azCount[evidx[i]];
+        ALuint evoffset = Hrtf->evOffset[evidx[i]];
+        ALuint azidx[2];
+
+        /* Calculate azimuth indices and interpolation factor for this elevation. */
+        CalcAzIndices(azcount, azimuth, azidx, &mu[i]);
+
+        /* Calculate a set of linear HRIR indices for left and right channels. */
+        lidx[i*2 + 0] = evoffset + azidx[0];
+        lidx[i*2 + 1] = evoffset + azidx[1];
+        ridx[i*2 + 0] = evoffset + ((azcount-azidx[0]) % azcount);
+        ridx[i*2 + 1] = evoffset + ((azcount-azidx[1]) % azcount);
+    }
+
+    // Calculate the stepping parameters.
+    delta = maxf(floorf(delta*(Hrtf->sampleRate*0.015f) + 0.5f), 1.0f);
+    step = 1.0f / delta;
+
+    /* Calculate 4 blending weights for 2D bilinear interpolation. */
+    blend[0] = (1.0f-mu[0]) * (1.0f-mu[2]);
+    blend[1] = (     mu[0]) * (1.0f-mu[2]);
+    blend[2] = (1.0f-mu[1]) * (     mu[2]);
+    blend[3] = (     mu[1]) * (     mu[2]);
+
+    /* Calculate the HRIR delays using linear interpolation.  Then calculate
+     * the delay stepping values using the target and previous running
+     * delays.
+     */
+    left = (ALfloat)(delays[0] - (delayStep[0] * counter));
+    right = (ALfloat)(delays[1] - (delayStep[1] * counter));
+
+    delays[0] = fastf2u((Hrtf->delays[lidx[0]]*blend[0] + Hrtf->delays[lidx[1]]*blend[1] +
+                         Hrtf->delays[lidx[2]]*blend[2] + Hrtf->delays[lidx[3]]*blend[3]) *
+                        dirfact + 0.5f) << HRTFDELAY_BITS;
+    delays[1] = fastf2u((Hrtf->delays[ridx[0]]*blend[0] + Hrtf->delays[ridx[1]]*blend[1] +
+                         Hrtf->delays[ridx[2]]*blend[2] + Hrtf->delays[ridx[3]]*blend[3]) *
+                        dirfact + 0.5f) << HRTFDELAY_BITS;
+
+    delayStep[0] = fastf2i(step * (delays[0] - left));
+    delayStep[1] = fastf2i(step * (delays[1] - right));
+
+    /* Calculate the sample offsets for the HRIR indices. */
+    lidx[0] *= Hrtf->irSize;
+    lidx[1] *= Hrtf->irSize;
+    lidx[2] *= Hrtf->irSize;
+    lidx[3] *= Hrtf->irSize;
+    ridx[0] *= Hrtf->irSize;
+    ridx[1] *= Hrtf->irSize;
+    ridx[2] *= Hrtf->irSize;
+    ridx[3] *= Hrtf->irSize;
+
+    /* Calculate the normalized and attenuated target HRIR coefficients using
+     * linear interpolation when there is enough gain to warrant it.  Zero
+     * the target coefficients if gain is too low.  Then calculate the
+     * coefficient stepping values using the target and previous running
+     * coefficients.
+     */
+    if(gain > 0.0001f)
+    {
+        ALfloat c;
+
+        i = 0;
+        left = coeffs[i][0] - (coeffStep[i][0] * counter);
+        right = coeffs[i][1] - (coeffStep[i][1] * counter);
+
+        c = (Hrtf->coeffs[lidx[0]+i]*blend[0] + Hrtf->coeffs[lidx[1]+i]*blend[1] +
+             Hrtf->coeffs[lidx[2]+i]*blend[2] + Hrtf->coeffs[lidx[3]+i]*blend[3]);
+        coeffs[i][0] = lerp(PassthruCoeff, c, dirfact) * gain * (1.0f/32767.0f);;
+        c = (Hrtf->coeffs[ridx[0]+i]*blend[0] + Hrtf->coeffs[ridx[1]+i]*blend[1] +
+             Hrtf->coeffs[ridx[2]+i]*blend[2] + Hrtf->coeffs[ridx[3]+i]*blend[3]);
+        coeffs[i][1] = lerp(PassthruCoeff, c, dirfact) * gain * (1.0f/32767.0f);;
+
+        coeffStep[i][0] = step * (coeffs[i][0] - left);
+        coeffStep[i][1] = step * (coeffs[i][1] - right);
+
+        for(i = 1;i < Hrtf->irSize;i++)
+        {
+            left = coeffs[i][0] - (coeffStep[i][0] * counter);
+            right = coeffs[i][1] - (coeffStep[i][1] * counter);
+
+            c = (Hrtf->coeffs[lidx[0]+i]*blend[0] + Hrtf->coeffs[lidx[1]+i]*blend[1] +
+                 Hrtf->coeffs[lidx[2]+i]*blend[2] + Hrtf->coeffs[lidx[3]+i]*blend[3]);
+            coeffs[i][0] = lerp(0.0f, c, dirfact) * gain * (1.0f/32767.0f);;
+            c = (Hrtf->coeffs[ridx[0]+i]*blend[0] + Hrtf->coeffs[ridx[1]+i]*blend[1] +
+                 Hrtf->coeffs[ridx[2]+i]*blend[2] + Hrtf->coeffs[ridx[3]+i]*blend[3]);
+            coeffs[i][1] = lerp(0.0f, c, dirfact) * gain * (1.0f/32767.0f);;
+
+            coeffStep[i][0] = step * (coeffs[i][0] - left);
+            coeffStep[i][1] = step * (coeffs[i][1] - right);
+        }
+    }
+    else
+    {
+        for(i = 0;i < Hrtf->irSize;i++)
+        {
+            left = coeffs[i][0] - (coeffStep[i][0] * counter);
+            right = coeffs[i][1] - (coeffStep[i][1] * counter);
+
+            coeffs[i][0] = 0.0f;
+            coeffs[i][1] = 0.0f;
+
+            coeffStep[i][0] = step * -left;
+            coeffStep[i][1] = step * -right;
+        }
+    }
+
+    /* The stepping count is the number of samples necessary for the HRIR to
+     * complete its transition.  The mixer will only apply stepping for this
+     * many samples.
+     */
+    return fastf2u(delta);
 }