Use correct HRTF elevation response for negative elevations.

Source/platform/audio/HRTFElevation.cpp

 /*
  * Copyright (C) 2010 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  *
  * 1.  Redistributions of source code must retain the above copyright
  *     notice, this list of conditions and the following disclaimer.
  * 2.  Redistributions in binary form must reproduce the above copyright
@@ skipping 39 matching lines @@
 const size_t TotalNumberOfResponses = 240;
 
 // Number of frames in an individual impulse response.
 const size_t ResponseFrameSize = 256;
 
 // Sample-rate of the spatialization impulse responses as stored in the resource file.
 // The impulse responses may be resampled to a different sample-rate (depending on the audio hardware) when they are loaded.
 const float ResponseSampleRate = 44100;
 
 #if USE(CONCATENATED_IMPULSE_RESPONSES)
+
+// This table maps the index into the elevation table with the corresponding angle. See
+// https://bugs.webkit.org/show_bug.cgi?id=98294#c9 for the elevation angles and their order in the
+// concatenated response.
+const int ElevationIndexTableSize = 10;
+const int ElevationIndexTable[ElevationIndexTableSize] = {
+    0, 15, 30, 45, 60, 75, 90, 315, 330, 345
+};
+
 // Lazily load a concatenated HRTF database for given subject and store it in a
 // local hash table to ensure quick efficient future retrievals.
 static PassRefPtr<AudioBus> getConcatenatedImpulseResponsesForSubject(const String& subjectName)
 {
     typedef HashMap<String, RefPtr<AudioBus> > AudioBusMap;
     DEFINE_STATIC_LOCAL(AudioBusMap, audioBusMap, ());
     DEFINE_STATIC_LOCAL(Mutex, mutex, ());
 
     MutexLocker locker(mutex);
     RefPtr<AudioBus> bus;
@@ skipping 43 matching lines @@
     // Note: the passed in subjectName is not a string passed in via JavaScript or the web.
     // It's passed in as an internal ASCII identifier and is an implementation detail.
     int positiveElevation = elevation < 0 ? elevation + 360 : elevation;
 
 #if USE(CONCATENATED_IMPULSE_RESPONSES)
     RefPtr<AudioBus> bus(getConcatenatedImpulseResponsesForSubject(subjectName));
 
     if (!bus)
         return false;
 
-    int elevationIndex = positiveElevation / AzimuthSpacing;
-    if (positiveElevation > 90)
-        elevationIndex -= AzimuthSpacing;
+    // Just sequentially search the table to find the correct index.
+    int elevationIndex = -1;
+
+    for (int k = 0; k < ElevationIndexTableSize; ++k) {
+        if (ElevationIndexTable[k] == positiveElevation) {
+            elevationIndex = k;
+            break;
+        }
+    }
+
+    bool isElevationIndexGood = (elevationIndex >= 0) && (elevationIndex < ElevationIndexTableSize);
+    ASSERT(isElevationIndexGood);
+    if (!isElevationIndexGood)
+        return false;
 
     // The concatenated impulse response is a bus containing all
     // the elevations per azimuth, for all azimuths by increasing
     // order. So for a given azimuth and elevation we need to compute
     // the index of the wanted audio frames in the concatenated table.
     unsigned index = ((azimuth / AzimuthSpacing) * HRTFDatabase::NumberOfRawElevations) + elevationIndex;
     bool isIndexGood = index < TotalNumberOfResponses;
     ASSERT(isIndexGood);
     if (!isIndexGood)
         return false;
@@ skipping 168 matching lines @@
     double frameDelay2R = m_kernelListR->at(azimuthIndex2)->frameDelay();
 
     // Linearly interpolate delays.
     frameDelayL = (1.0 - azimuthBlend) * frameDelayL + azimuthBlend * frameDelay2L;
     frameDelayR = (1.0 - azimuthBlend) * frameDelayR + azimuthBlend * frameDelay2R;
 }
 
 } // namespace blink
 
 #endif // ENABLE(WEB_AUDIO)