third_party/WebKit/Source/platform/audio/DistanceEffect.cpp

/*
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#include "platform/audio/DistanceEffect.h"

#include <math.h>
#include <algorithm>
#include "platform/wtf/Assertions.h"
#include "platform/wtf/MathExtras.h"

namespace blink {

DistanceEffect::DistanceEffect()
    : model_(kModelInverse),
      ref_distance_(1.0),
      max_distance_(10000.0),
      rolloff_factor_(1.0) {}

double DistanceEffect::Gain(double distance) {
  switch (model_) {
    case kModelLinear:
      return LinearGain(distance);
    case kModelInverse:
      return InverseGain(distance);
    case kModelExponential:
      return ExponentialGain(distance);
  }
  NOTREACHED();
  return 0.0;
}

double DistanceEffect::LinearGain(double distance) {
  // Clamp refDistance and distance according to the spec.
  double dref = std::min(ref_distance_, max_distance_);
  double dmax = std::max(ref_distance_, max_distance_);
  distance = clampTo(distance, dref, dmax);

  if (dref == dmax)
    return 1 - rolloff_factor_;

  // We want a gain that decreases linearly from m_refDistance to
  // m_maxDistance. The gain is 1 at m_refDistance.
  return (1.0 - clampTo(rolloff_factor_, 0.0, 1.0) * (distance - dref) /
                    (dmax - dref));
}

double DistanceEffect::InverseGain(double distance) {
  if (ref_distance_ == 0)
    return 0;

  // Clamp distance according to spec
  distance = clampTo(distance, ref_distance_);

  return ref_distance_ / (ref_distance_ + clampTo(rolloff_factor_, 0.0) *
                                              (distance - ref_distance_));
}

double DistanceEffect::ExponentialGain(double distance) {
  if (ref_distance_ == 0)
    return 0;

  // Clamp distance according to spec
  distance = clampTo(distance, ref_distance_);

  return pow(distance / ref_distance_, -clampTo(rolloff_factor_, 0.0));
}

}  // namespace blink