text: /*
   * Copyright (C) 2011 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 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 DynamicsCompressorKernel_h
  #define DynamicsCompressorKernel_h
  
  #include "AudioArray.h"
  #include <memory>
  #include <wtf/Vector.h>
  
  namespace WebCore {
  
  class DynamicsCompressorKernel {
  public:
      DynamicsCompressorKernel(float sampleRate, unsigned numberOfChannels);
  
      void setNumberOfChannels(unsigned);
  
      // Performs stereo-linked compression.
      void process(float* sourceChannels[],
                   float* destinationChannels[],
                   unsigned numberOfChannels,
                   unsigned framesToProcess,
  
                   float dbThreshold,
                   float dbKnee,
                   float ratio,
                   float attackTime,
                   float releaseTime,
                   float preDelayTime,
                   float dbPostGain,
                   float effectBlend,
  
                   float releaseZone1,
                   float releaseZone2,
                   float releaseZone3,
                   float releaseZone4
                   );
  
      void reset();
  
      unsigned latencyFrames() const { return m_lastPreDelayFrames; }
  
      float sampleRate() const { return m_sampleRate; }
  
      float meteringGain() const { return m_meteringGain; }
  
  protected:
      float m_sampleRate;
  
      float m_detectorAverage;
      float m_compressorGain;
  
      // Metering
      float m_meteringReleaseK;
      float m_meteringGain;
  
      // Lookahead section.
      enum { MaxPreDelayFrames = 1024 };
      enum { MaxPreDelayFramesMask = MaxPreDelayFrames - 1 };
      enum { DefaultPreDelayFrames = 256 }; // setPreDelayTime() will override this initial value
      unsigned m_lastPreDelayFrames;
      void setPreDelayTime(float);
  
      Vector<std::unique_ptr<AudioFloatArray>> m_preDelayBuffers;
      int m_preDelayReadIndex;
      int m_preDelayWriteIndex;
  
      float m_maxAttackCompressionDiffDb;
  
      // Static compression curve.
      float kneeCurve(float x, float k);
      float saturate(float x, float k);
      float slopeAt(float x, float k);
      float kAtSlope(float desiredSlope);
  
      float updateStaticCurveParameters(float dbThreshold, float dbKnee, float ratio);
  
      // Amount of input change in dB required for 1 dB of output change.
      // This applies to the portion of the curve above m_kneeThresholdDb (see below).
      float m_ratio;
      float m_slope; // Inverse ratio.
  
      // The input to output change below the threshold is linear 1:1.
      float m_linearThreshold;
      float m_dbThreshold;
  
      // m_dbKnee is the number of dB above the threshold before we enter the "ratio" portion of the curve.
      // m_kneeThresholdDb = m_dbThreshold + m_dbKnee
      // The portion between m_dbThreshold and m_kneeThresholdDb is the "soft knee" portion of the curve
      // which transitions smoothly from the linear portion to the ratio portion.
      float m_dbKnee;
      float m_kneeThreshold;
      float m_kneeThresholdDb;
      float m_ykneeThresholdDb;
  
      // Internal parameter for the knee portion of the curve.
      float m_K;
  };
  
  } // namespace WebCore
  
  #endif // DynamicsCompressorKernel_h
  