Initial commit

Author: Elli Beres

.gitignore

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+.vscode
+.DS_Store
+

README.md

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+# 2D OpenSimplex Noise
+
+Ported from Python implementation [here](https://github.com/lmas/opensimplex).
+
+## IMPORTANT
+
+For actual production code, use [this port](https://github.com/ojrac/opensimplex-go) instead.

go.mod

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+module github.com/ellifteria/opensimplex2-go
+
+go 1.20
+
+require github.com/ojrac/opensimplex-go v1.0.2

go.sum

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+github.com/ojrac/opensimplex-go v1.0.2 h1:l4vs0D+JCakcu5OV0kJ99oEaWJfggSc9jiLpxaWvSzs=
+github.com/ojrac/opensimplex-go v1.0.2/go.mod h1:NwbXFFbXcdGgIFdiA7/REME+7n/lOf1TuEbLiZYOWnM=

opensimplex2.go

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+package opensimplex2
+
+import "math"
+
+type Noise interface {
+	Noise2D(x, y float64) float64
+}
+
+type noise struct {
+	perm []int16
+}
+
+func NewNoise(seed int64) Noise {
+	n := &noise{perm: make([]int16, 256)}
+
+	var source [256]int16
+
+	for i := range source {
+		source[i] = int16(i)
+	}
+
+	seed = seed*6364136223846793005 + 1442695040888963407
+	seed = seed*6364136223846793005 + 1442695040888963407
+	seed = seed*6364136223846793005 + 1442695040888963407
+
+	var i int32
+	for i = 255; i >= 0; i-- {
+		seed = seed*6364136223846793005 + 1442695040888963407
+		r := int32((seed + 31) % int64(i+1))
+		if r < 0 {
+			r += i + 1
+		}
+
+		n.perm[i] = source[r]
+		source[r] = source[i]
+	}
+
+	return n
+}
+
+func (n *noise) Noise2D(x, y float64) float64 {
+
+	var noisyValue float64
+
+	stretchOffset := (x + y) * StretchConstant2
+	xs := x + stretchOffset
+	ys := y + stretchOffset
+
+	xsb := math.Floor(xs)
+	ysb := math.Floor(ys)
+
+	squishOffset := (xsb + ysb) * SquishConstant2
+	xb := xsb + squishOffset
+	yb := ysb + squishOffset
+
+	xins := xs - xsb
+	yins := ys - ysb
+
+	inSum := xins + yins
+
+	dx0 := x - xb
+	dy0 := y - yb
+
+	var value float64 = 0.0
+
+	dx1 := dx0 - 1 - SquishConstant2
+	dy1 := dy0 - 0 - SquishConstant2
+	attn1 := 2 - dx1*dx1 - dy1*dy1
+	if attn1 > 0 {
+		attn1 *= attn1
+		value += attn1 * attn1 * extrapolate2(n.perm[:], xsb+1, ysb+0, dx1, dy1)
+	}
+
+	dx2 := dx0 - 0 - SquishConstant2
+	dy2 := dy0 - 1 - SquishConstant2
+	attn2 := 2 - dx2*dx2 - dy2*dy2
+	if attn2 > 0 {
+		attn2 *= attn2
+		value += attn2 * attn2 * extrapolate2(n.perm[:], xsb+0, ysb+1, dx2, dy2)
+	}
+
+	var xsvExt, ysvExt, dxExt, dyExt float64
+	if inSum <= 1 {
+		zins := 1 - inSum
+		if zins > xins || zins > yins {
+			if xins > yins {
+				xsvExt = xsb + 1
+				ysvExt = ysb - 1
+				dxExt = dx0 - 1
+				dyExt = dy0 + 1
+			} else {
+				xsvExt = xsb - 1
+				ysvExt = ysb + 1
+				dxExt = dx0 + 1
+				dyExt = dy0 - 1
+			}
+		} else {
+			xsvExt = xb + 1
+			ysvExt = ysb + 1
+			dxExt = dx0 - 1 - 2*SquishConstant2
+			dyExt = dy0 - 1 - 2*SquishConstant2
+		}
+	} else {
+		zins := 2 - inSum
+		if zins < xins || zins < yins {
+			if xins > yins {
+				xsvExt = xsb + 2
+				ysvExt = ysb + 0
+				dxExt = dx0 - 2 - 2*SquishConstant2
+				dyExt = dy0 + 0 - 2*SquishConstant2
+			} else {
+				xsvExt = xsb + 0
+				ysvExt = ysb + 2
+				dxExt = dx0 + 0 - 2*SquishConstant2
+				dyExt = dy0 - 2 - 2*SquishConstant2
+			}
+		} else {
+			xsvExt = xsb
+			ysvExt = ysb
+			dxExt = dx0
+			dyExt = dy0
+		}
+
+		xsb += 1
+		ysb += 1
+		dx0 = dx0 - 1 - 2*SquishConstant2
+		dy0 = dy0 - 1 - 2*SquishConstant2
+	}
+
+	attn0 := 2 - dx0*dx0 - dy0*dy0
+	if attn0 > 0 {
+		attn0 *= attn0
+		value += attn0 * attn0 * extrapolate2(n.perm[:], xsb, ysb, dx0, dy0)
+	}
+
+	attnExt := 2 - dxExt*dxExt - dyExt*dyExt
+	if attnExt > 0 {
+		attnExt *= attnExt
+		value += attnExt * attnExt * extrapolate2(n.perm[:], xsvExt, ysvExt, dxExt, dyExt)
+	}
+
+	noisyValue = value / NormConstant2
+
+	return noisyValue
+}
+
+func extrapolate2(perm []int16, xsb, ysb, dx, dy float64) float64 {
+	index := perm[(int32(perm[int32(xsb)&0xff])+int32(ysb))&0xff] & 0x0e
+	g1 := float64(Gradients2[index])
+	g2 := float64(Gradients2[index+1])
+
+	return g1*dx + g2*dy
+}

opensimplex2_constants.go

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+package opensimplex2
+
+const (
+	StretchConstant2 float64 = -0.21132486540518708
+	SquishConstant2  float64 = 0.3660254037844386
+	NormConstant2    float64 = 47
+)
+
+var Gradients2 [16]int8 = [16]int8{
+	5, 2, 2, 5,
+	-5, 2, -2, 5,
+	5, -2, 2, -5,
+	-5, -2, -2, -5,
+}

opensimplex2_test.go

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+package opensimplex2
+
+import (
+	"math"
+	"testing"
+
+	"github.com/ojrac/opensimplex-go"
+)
+
+func TestConstants(t *testing.T) {
+	trueStretch := (1.0/math.Sqrt(2.0+1.0) - 1.0) / 2.0
+	trueSquish := (math.Sqrt(2.0+1.0) - 1.0) / 2.0
+	tolerance := math.Pow10(-14)
+
+	if math.Abs(StretchConstant2-trueStretch) > tolerance {
+		t.Errorf("Stretch constant incorrect; got %f, expected %f",
+			StretchConstant2, trueStretch)
+	}
+
+	if math.Abs(SquishConstant2-trueSquish) > tolerance {
+		t.Errorf("Squish constant incorrect; got %f, expected %f",
+			SquishConstant2, trueSquish)
+	}
+}
+
+func TestNoise2D(t *testing.T) {
+	var seed int64 = 298610
+	x, y := 14.0, 12.0
+	tolerance := math.Pow10(-14)
+
+	testNoise := NewNoise(seed)
+	testValue := testNoise.Noise2D(x, y)
+
+	libNoise := opensimplex.New(seed)
+	libValue := libNoise.Eval2(x, y)
+
+	if math.Abs(testValue-libValue) > tolerance {
+		t.Errorf("Inconsistent noise result; got %f, expected %f",
+			testValue, libValue)
+	}
+
+}