package gen

type DoublePerlin struct {
	Amplitude float64
	A         Octave
	B         Octave
}

func DoublePerlinFromXoroshiro(x *Xoroshiro, amplitudes []float64, omin int, lenn int, nmax int) (d DoublePerlin) {
	na := -1
	nb := -1
	if nmax > 0 {
		na = (nmax + 1) >> 1
		nb = nmax - na
	}
	d.A = OctaveFromXoroshiro(x, amplitudes, omin, lenn, na)
	d.B = OctaveFromXoroshiro(x, amplitudes, omin, lenn, nb)

	for i := lenn - 1; i >= 0 && amplitudes[i] == 0.0; i-- {
		lenn--
	}
	for i := 0; amplitudes[i] == 0.0; i++ {
		lenn--
	}
	var ampInits = []float64{
		0, 5. / 6, 10. / 9, 15. / 12, 20. / 15, 25. / 18, 30. / 21, 35. / 24, 40. / 27, 45. / 30,
		50. / 33, 55. / 36, 60. / 39, 65. / 42, 70. / 45, 75. / 48, 80. / 51,
	}
	d.Amplitude = ampInits[lenn]
	return
}

const DoublePerlinNoiseFactor = 337.0 / 331.0

func (d *DoublePerlin) Sample(x, y, z float64) float64 {
	return d.Amplitude * (d.A.Sample(x, y, z) + d.B.Sample(x*DoublePerlinNoiseFactor, y*DoublePerlinNoiseFactor, z*DoublePerlinNoiseFactor))
}