Add an HRTF filter for mono sources

The data is based on the KEMAR HRTF data provided by MIT, which can be found at
<http://sound.media.mit.edu/resources/KEMAR.html>. The compact measurements
were used. See hrtf_tables.inc for more information.

The filter is only available for stereo output, using a 44100hz playback rate.
Note also that it currently only applies to mono sounds, and the cf_level and
head_dampen config options are ignored while it is active.

1 files changed, 75 insertions, 0 deletions

diff --git a/Alc/hrtf.c b/Alc/hrtf.c
new file mode 100644
index 00000000..6972ec27
--- /dev/null
+++ b/Alc/hrtf.c
@@ -0,0 +1,75 @@
+/**
+ * OpenAL cross platform audio library
+ * Copyright (C) 2011 by Chris Robinson
+ * This library is free software; you can redistribute it and/or
+ *  modify it under the terms of the GNU Library General Public
+ *  License as published by the Free Software Foundation; either
+ *  version 2 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ *  Library General Public License for more details.
+ *
+ * You should have received a copy of the GNU Library General Public
+ *  License along with this library; if not, write to the
+ *  Free Software Foundation, Inc., 59 Temple Place - Suite 330,
+ *  Boston, MA  02111-1307, USA.
+ * Or go to http://www.gnu.org/copyleft/lgpl.html
+ */
+
+#include "config.h"
+
+#include "AL/al.h"
+#include "AL/alc.h"
+#include "alMain.h"
+
+
+typedef struct {
+    ALsizei num_angles;
+    ALshort coeffs[][2][HRTF_LENGTH];
+} HrtfFilterCoeffs;
+
+#include "hrtf_tables.inc"
+
+static void get_angle_coeffs(const HrtfFilterCoeffs *elev, ALfloat angle, const ALshort **left, const ALshort **right)
+{
+    if(angle < 0)
+    {
+        int idx = ((angle > -180.0) ? (int)(angle*(elev->num_angles-1)/-180.0 + 0.5) :
+                                      (elev->num_angles-1));
+        *left  = elev->coeffs[idx][1];
+        *right = elev->coeffs[idx][0];
+    }
+    else
+    {
+        int idx = ((angle < 180.0) ? (int)(angle*(elev->num_angles-1)/180.0 + 0.5) :
+                                     (elev->num_angles-1));
+        *left  = elev->coeffs[idx][0];
+        *right = elev->coeffs[idx][1];
+    }
+}
+
+void GetHrtfCoeffs(ALfloat azimuth, ALfloat angle, const ALshort **left, const ALshort **right)
+{
+    int idx;
+
+    if(azimuth > 90.f) azimuth = 90.f - (azimuth - 90.f);
+    else if(azimuth < -90.f) azimuth = -90.f - (azimuth - -90.f);
+
+    idx = (int)(azimuth/10.0 + 0.5);
+    if(idx >= 9) return get_angle_coeffs(&Elev90, angle, left, right);
+    if(idx >= 8) return get_angle_coeffs(&Elev80, angle, left, right);
+    if(idx >= 7) return get_angle_coeffs(&Elev70, angle, left, right);
+    if(idx >= 6) return get_angle_coeffs(&Elev60, angle, left, right);
+    if(idx >= 5) return get_angle_coeffs(&Elev50, angle, left, right);
+    if(idx >= 4) return get_angle_coeffs(&Elev40, angle, left, right);
+    if(idx >= 3) return get_angle_coeffs(&Elev30, angle, left, right);
+    if(idx >= 2) return get_angle_coeffs(&Elev20, angle, left, right);
+    if(idx >= 1) return get_angle_coeffs(&Elev10, angle, left, right);
+    if(idx >= 0) return get_angle_coeffs(&Elev0, angle, left, right);
+    if(idx >= -1) return get_angle_coeffs(&Elev10n, angle, left, right);
+    if(idx >= -2) return get_angle_coeffs(&Elev20n, angle, left, right);
+    if(idx >= -3) return get_angle_coeffs(&Elev30n, angle, left, right);
+    return get_angle_coeffs(&Elev40n, angle, left, right);
+}