text: /*
   * 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
   *     notice, this list of conditions and the following disclaimer in the
   *     documentation and/or other materials provided with the distribution.
   * 3.  Neither the name of Apple Computer, Inc. ("Apple") nor the names of
   *     its contributors may be used to endorse or promote products derived
   *     from this software without specific prior written permission.
   *
   * THIS SOFTWARE IS PROVIDED BY APPLE AND ITS CONTRIBUTORS "AS IS" AND ANY
   * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
   * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
   * DISCLAIMED. IN NO EVENT SHALL APPLE OR ITS CONTRIBUTORS BE LIABLE FOR ANY
   * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
   * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
   * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
   * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
   * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
   * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
   */
  
  #ifndef HRTFKernel_h
  #define HRTFKernel_h
  
  #include "platform/audio/FFTFrame.h"
  #include "wtf/Allocator.h"
  #include "wtf/Noncopyable.h"
  #include "wtf/PtrUtil.h"
  #include "wtf/Vector.h"
  #include <memory>
  
  namespace blink {
  
  class AudioChannel;
  
  // HRTF stands for Head-Related Transfer Function.
  // HRTFKernel is a frequency-domain representation of an impulse-response used as part of the spatialized panning system.
  // For a given azimuth / elevation angle there will be one HRTFKernel for the left ear transfer function, and one for the right ear.
  // The leading delay (average group delay) for each impulse response is extracted:
  //      m_fftFrame is the frequency-domain representation of the impulse response with the delay removed
  //      m_frameDelay is the leading delay of the original impulse response.
  class PLATFORM_EXPORT HRTFKernel {
      USING_FAST_MALLOC(HRTFKernel);
      WTF_MAKE_NONCOPYABLE(HRTFKernel);
  public:
      // Note: this is destructive on the passed in AudioChannel.
      // The length of channel must be a power of two.
      static std::unique_ptr<HRTFKernel> create(AudioChannel* channel, size_t fftSize, float sampleRate)
      {
          return wrapUnique(new HRTFKernel(channel, fftSize, sampleRate));
      }
  
      static std::unique_ptr<HRTFKernel> create(std::unique_ptr<FFTFrame> fftFrame, float frameDelay, float sampleRate)
      {
          return wrapUnique(new HRTFKernel(std::move(fftFrame), frameDelay, sampleRate));
      }
  
      // Given two HRTFKernels, and an interpolation factor x: 0 -> 1, returns an interpolated HRTFKernel.
      static std::unique_ptr<HRTFKernel> createInterpolatedKernel(HRTFKernel* kernel1, HRTFKernel* kernel2, float x);
  
      FFTFrame* fftFrame() { return m_fftFrame.get(); }
  
      size_t fftSize() const { return m_fftFrame->fftSize(); }
      float frameDelay() const { return m_frameDelay; }
  
      float sampleRate() const { return m_sampleRate; }
      double nyquist() const { return 0.5 * sampleRate(); }
  
      // Converts back into impulse-response form.
      std::unique_ptr<AudioChannel> createImpulseResponse();
  
  private:
      // Note: this is destructive on the passed in AudioChannel.
      HRTFKernel(AudioChannel*, size_t fftSize, float sampleRate);
  
      HRTFKernel(std::unique_ptr<FFTFrame> fftFrame, float frameDelay, float sampleRate)
          : m_fftFrame(std::move(fftFrame))
          , m_frameDelay(frameDelay)
          , m_sampleRate(sampleRate)
      {
      }
  
      std::unique_ptr<FFTFrame> m_fftFrame;
      float m_frameDelay;
      float m_sampleRate;
  };
  
  typedef Vector<std::unique_ptr<HRTFKernel>> HRTFKernelList;
  
  } // namespace blink
  
  #endif // HRTFKernel_h
  