PerlinNoise Dart

import 'dart:math' as Math;

class PerlinNoise {
  int _seed;
  int _octaves;
  double _persistence;


  PerlinNoise ({seed:null,octaves: 1,persistence:1.0}) {
    if (seed == null) {
      Math.Random rand = new Math.Random();
      _seed = rand.nextInt(999999999);
    } else
      _seed = seed;
    _octaves = octaves;
    _persistence = persistence;
  }

  double _noise(int x, int y) {
    Math.Random rand = new Math.Random(x+y+_seed);
    return ((rand.nextDouble()*2)-1);
  }

  double _smoothNoise (int x, int y) {
    double corners = (_noise(x-1,y-1)+_noise(x+1,y-1)+_noise(x-1,y+1)+_noise(x+1,y+1))/16;
    double sides  =(_noise(x-1,y)+_noise(x+1,y)+_noise(x,y-1)+_noise(x,y+1))/8;
    double center = _noise(x,y)/4;
    return corners+sides+center;
  }

  double _interpolate (double a,double b,double x) {
    double ft = x * Math.PI;
    double f = (1-Math.cos(ft))*.5;
    return (a*(1-f) + b*f);
  }

  double _interpolatedNoise (double x, double y) {
    int intX = x.floor();
    int intY = y.floor();

    double fracX = x-intX;
    double fracY = x-intY;

    double v1 = _smoothNoise(intX, intY);
    double v2 = _smoothNoise(intX+1, intY);
    double v3 = _smoothNoise(intX, intY+1);
    double v4 = _smoothNoise(intX+1, intY+1);

    double i1 = _interpolate(v1,v2,fracX);
    double i2 = _interpolate(v3,v4,fracX);

    return _interpolate(i1,i2,fracY);
  }

  double perlinNoise(double x, double y) {
    var total = 0;

    for (var i=0; i<_octaves; i++) {
      int frequency = Math.pow(2, i);
      double amplitude = Math.pow(_persistence, i);

      total +=_interpolatedNoise(x*frequency, y*frequency)*amplitude;
    }
    return total;
  }
}