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 THIRD_PARTY_BLINK_RENDERER_PLATFORM_AUDIO_HRTF_KERNEL_H_
  #define THIRD_PARTY_BLINK_RENDERER_PLATFORM_AUDIO_HRTF_KERNEL_H_
  
  #include <memory>
  #include <utility>
  
  #include "base/macros.h"
  #include "base/memory/ptr_util.h"
  #include "third_party/blink/renderer/platform/audio/fft_frame.h"
  #include "third_party/blink/renderer/platform/wtf/allocator/allocator.h"
  #include "third_party/blink/renderer/platform/wtf/vector.h"
  
  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);
  
   public:
    // Note: this is destructive on the passed in AudioChannel.
    // The length of channel must be a power of two.
    HRTFKernel(AudioChannel*, size_t fft_size, float sample_rate);
    HRTFKernel(std::unique_ptr<FFTFrame> fft_frame,
               float frame_delay,
               float sample_rate)
        : fft_frame_(std::move(fft_frame)),
          frame_delay_(frame_delay),
          sample_rate_(sample_rate) {}
  
    // 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 fft_frame_.get(); }
  
    size_t FftSize() const { return fft_frame_->FftSize(); }
    float FrameDelay() const { return frame_delay_; }
  
    float SampleRate() const { return sample_rate_; }
    double Nyquist() const { return 0.5 * SampleRate(); }
  
   private:
    std::unique_ptr<FFTFrame> fft_frame_;
    float frame_delay_;
    float sample_rate_;
  
    DISALLOW_COPY_AND_ASSIGN(HRTFKernel);
  };
  
  typedef Vector<std::unique_ptr<HRTFKernel>> HRTFKernelList;
  
  }  // namespace blink
  
  #endif  // THIRD_PARTY_BLINK_RENDERER_PLATFORM_AUDIO_HRTF_KERNEL_H_
  