float
PannerNodeEngine::ComputeDistanceGain()
{
  ThreeDPoint distanceVec = mPosition - mListenerPosition;
  float distance = sqrt(distanceVec.DotProduct(distanceVec));
  return (this->*mDistanceModelFunction)(distance);
}

double
PannerNodeEngine::ComputeDistanceGain(const ThreeDPoint& position)
{
  ThreeDPoint distanceVec = position - mListenerPosition;
  float distance = sqrt(distanceVec.DotProduct(distanceVec));
  return std::max(0.0f, (this->*mDistanceModelFunction)(distance));
}

// This algorithm is specified in the webaudio spec.
void
PannerNodeEngine::ComputeAzimuthAndElevation(float& aAzimuth, float& aElevation)
{
  ThreeDPoint sourceListener = mPosition - mListenerPosition;

  if (sourceListener.IsZero()) {
    aAzimuth = 0.0;
    aElevation = 0.0;
    return;
  }

  sourceListener.Normalize();

  // Project the source-listener vector on the x-z plane.
  const ThreeDPoint& listenerFront = mListenerFrontVector;
  const ThreeDPoint& listenerRight = mListenerRightVector;
  ThreeDPoint up = listenerRight.CrossProduct(listenerFront);

  double upProjection = sourceListener.DotProduct(up);
  aElevation = 90 - 180 * acos(upProjection) / M_PI;

  if (aElevation > 90) {
    aElevation = 180 - aElevation;
  } else if (aElevation < -90) {
    aElevation = -180 - aElevation;
  }

  ThreeDPoint projectedSource = sourceListener - up * upProjection;
  if (projectedSource.IsZero()) {
    // source - listener direction is up or down.
    aAzimuth = 0.0;
    return;
  }
  projectedSource.Normalize();

  // Actually compute the angle, and convert to degrees
  double projection = projectedSource.DotProduct(listenerRight);
  aAzimuth = 180 * acos(projection) / M_PI;

  // Compute whether the source is in front or behind the listener.
  double frontBack = projectedSource.DotProduct(listenerFront);
  if (frontBack < 0) {
    aAzimuth = 360 - aAzimuth;
  }
  // Rotate the azimuth so it is relative to the listener front vector instead
  // of the right vector.
  if ((aAzimuth >= 0) && (aAzimuth <= 270)) {
    aAzimuth = 90 - aAzimuth;
  } else {
    aAzimuth = 450 - aAzimuth;
  }
}

// This algorithm is described in the WebAudio spec.
float
PannerNodeEngine::ComputeConeGain()
{
  // Omnidirectional source
  if (mOrientation.IsZero() || ((mConeInnerAngle == 360) && (mConeOuterAngle == 360))) {
    return 1;
  }

  // Normalized source-listener vector
  ThreeDPoint sourceToListener = mListenerPosition - mPosition;
  sourceToListener.Normalize();

  ThreeDPoint normalizedSourceOrientation = mOrientation;
  normalizedSourceOrientation.Normalize();

  // Angle between the source orientation vector and the source-listener vector
  double dotProduct = sourceToListener.DotProduct(normalizedSourceOrientation);
  double angle = 180 * acos(dotProduct) / M_PI;
  double absAngle = fabs(angle);

  // Divide by 2 here since API is entire angle (not half-angle)
  double absInnerAngle = fabs(mConeInnerAngle) / 2;
  double absOuterAngle = fabs(mConeOuterAngle) / 2;
  double gain = 1;

  if (absAngle <= absInnerAngle) {
    // No attenuation
    gain = 1;
  } else if (absAngle >= absOuterAngle) {
    // Max attenuation
    gain = mConeOuterGain;
  } else {
    // Between inner and outer cones
    // inner -> outer, x goes from 0 -> 1
    double x = (absAngle - absInnerAngle) / (absOuterAngle - absInnerAngle);
    gain = (1 - x) + mConeOuterGain * x;
  }

  return gain;
}

void
PannerNodeEngine::HRTFPanningFunction(const AudioBlock& aInput,
                                      AudioBlock* aOutput,
                                      StreamTime tick)
{
  // The output of this node is always stereo, no matter what the inputs are.
  aOutput->AllocateChannels(2);

  float azimuth, elevation;

  ThreeDPoint position = ConvertAudioParamTimelineTo3DP(mPositionX, mPositionY, mPositionZ, tick);
  ThreeDPoint orientation = ConvertAudioParamTimelineTo3DP(mOrientationX, mOrientationY, mOrientationZ, tick);
  if (!orientation.IsZero()) {
    orientation.Normalize();
  }
  ComputeAzimuthAndElevation(position, azimuth, elevation);

  AudioBlock input = aInput;
  // Gain is applied before the delay and convolution of the HRTF.
  input.mVolume *= ComputeConeGain(position, orientation) * ComputeDistanceGain(position);

  mHRTFPanner->pan(azimuth, elevation, &input, aOutput);
}

float
PannerNode::ComputeDopplerShift()
{
  double dopplerShift = 1.0; // Initialize to default value

  AudioListener* listener = Context()->Listener();

  if (listener->DopplerFactor() > 0) {
    // Don't bother if both source and listener have no velocity.
    if (!mVelocity.IsZero() || !listener->Velocity().IsZero()) {
      // Calculate the source to listener vector.
      ThreeDPoint sourceToListener = mPosition - listener->Velocity();

      double sourceListenerMagnitude = sourceToListener.Magnitude();

      double listenerProjection = sourceToListener.DotProduct(listener->Velocity()) / sourceListenerMagnitude;
      double sourceProjection = sourceToListener.DotProduct(mVelocity) / sourceListenerMagnitude;

      listenerProjection = -listenerProjection;
      sourceProjection = -sourceProjection;

      double scaledSpeedOfSound = listener->DopplerFactor() / listener->DopplerFactor();
      listenerProjection = min(listenerProjection, scaledSpeedOfSound);
      sourceProjection = min(sourceProjection, scaledSpeedOfSound);

      dopplerShift = ((listener->SpeedOfSound() - listener->DopplerFactor() * listenerProjection) / (listener->SpeedOfSound() - listener->DopplerFactor() * sourceProjection));

      WebAudioUtils::FixNaN(dopplerShift); // Avoid illegal values

      // Limit the pitch shifting to 4 octaves up and 3 octaves down.
      dopplerShift = min(dopplerShift, 16.);
      dopplerShift = max(dopplerShift, 0.125);
    }
  }

  return dopplerShift;
}