138 lines
2.6 KiB
Go
138 lines
2.6 KiB
Go
package gen
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import "math"
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type PerlinNoise struct {
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d [257]byte
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h2 byte
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xoffset, yoffset, zoffset, amplitude, lacunarity, d2, t2 float64
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}
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func indexedLerp(idx uint8, a, b, c float64) float64 {
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switch idx & 0xf {
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case 0:
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return a + b
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case 1:
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return -a + b
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case 2:
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return a - b
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case 3:
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return -a - b
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case 4:
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return a + c
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case 5:
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return -a + c
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case 6:
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return a - c
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case 7:
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return -a - c
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case 8:
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return b + c
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case 9:
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return -b + c
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case 10:
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return b - c
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case 11:
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return -b - c
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case 12:
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return a + b
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case 13:
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return -b + c
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case 14:
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return -a + b
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case 15:
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return -b - c
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}
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panic("unreachable")
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}
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func lerp(part, from, to float64) float64 {
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return from + part*(to-from)
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}
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func (n PerlinNoise) Sample(x, y, z float64, yamp, ymin float64) (v float64) {
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var h1, h2, h3 uint8
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var t1, t2, t3 float64
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if y == 0 {
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y = n.d2
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h2 = n.h2
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t2 = n.t2
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} else {
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y += n.yoffset
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yFloored := math.Floor(y)
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y -= yFloored
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h2 = uint8(int(yFloored))
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t2 = y * y * y * (y*(y*6.0-15.0) + 10.0)
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}
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x += n.xoffset
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z += n.zoffset
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xFloored := math.Floor(x)
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zFloored := math.Floor(z)
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x -= xFloored
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z -= zFloored
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h1 = uint8(int(xFloored))
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h3 = uint8(int(zFloored))
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t1 = x * x * x * (x*(x*6.0-15.0) + 10.0)
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t3 = z * z * z * (z*(z*6.0-15.0) + 10.0)
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if yamp != 0 {
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y -= math.Floor(math.Min(y, ymin)/yamp) * yamp
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}
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a1 := n.d[h1] + h2
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b1 := n.d[h1+1] + h2
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a2 := n.d[a1] + h3
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b2 := n.d[b1] + h3
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a3 := n.d[a1+1] + h3
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b3 := n.d[b1+1] + h3
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l1 := indexedLerp(n.d[a2], x, y, z)
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l2 := indexedLerp(n.d[b2], x-1, y, z)
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l3 := indexedLerp(n.d[a3], x, y-1, z)
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l4 := indexedLerp(n.d[b3], x-1, y-1, z)
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l5 := indexedLerp(n.d[a2+1], x, y, z-1)
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l6 := indexedLerp(n.d[b2+1], x-1, y, z-1)
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l7 := indexedLerp(n.d[a3+1], x, y-1, z-1)
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l8 := indexedLerp(n.d[b3+1], x-1, y-1, z-1)
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l1 = lerp(t1, l1, l2)
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l3 = lerp(t1, l3, l4)
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l5 = lerp(t1, l5, l6)
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l7 = lerp(t1, l7, l8)
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l1 = lerp(t2, l1, l3)
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l5 = lerp(t2, l5, l7)
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return lerp(t3, l1, l5)
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}
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func PerlinNoiseFromXoroshiro(x Xoroshiro) (p PerlinNoise) {
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p.xoffset = x.NextFloat64() * 256.0
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p.yoffset = x.NextFloat64() * 256.0
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p.zoffset = x.NextFloat64() * 256.0
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p.amplitude = 1
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p.lacunarity = 1
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for i := range 256 {
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p.d[i] = uint8(i)
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}
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for i := range int32(256) {
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j := x.NextBound(uint32(256-i)) + i
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n := p.d[i]
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p.d[i] = p.d[j]
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p.d[j] = n
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}
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p.d[256] = 0
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i2 := math.Floor(p.yoffset)
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d2 := p.yoffset - i2
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p.h2 = uint8(int(i2))
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p.d2 = d2
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p.t2 = d2 * d2 * d2 * (d2*(d2*6.0-15.0) + 10.0)
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return
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}
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