From ca593e6a6e337af7e787c83be44e5b9102e3e66a Mon Sep 17 00:00:00 2001
From: Yongwei Xing <yongwei.xing@liulishuo.com>
Date: Tue, 2 Mar 2021 13:10:14 +0800
Subject: [PATCH] add julia set

---
 example/example_julia.go | 25 +++++++++++++++++++++++++
 julia.go                 | 40 ++++++++++++++++++++++++++++++++++++++++
 2 files changed, 65 insertions(+)
 create mode 100644 example/example_julia.go
 create mode 100644 julia.go

diff --git a/example/example_julia.go b/example/example_julia.go
new file mode 100644
index 0000000..c4b4c82
--- /dev/null
+++ b/example/example_julia.go
@@ -0,0 +1,25 @@
+package main
+
+import (
+	"generativeart"
+	"math/rand"
+	"time"
+)
+
+func julia1(z complex128) complex128 {
+	c := complex(-0.1, 0.651)
+
+	z = z*z + c
+
+	return z
+}
+
+func main() {
+	rand.Seed(time.Now().Unix())
+	c := generativeart.NewCanva(800, 800, 1.5, 1.5)
+	c.SetIterations(800)
+	c.SetColorSchema(generativeart.Viridis)
+	c.FillBackground()
+	c.Draw(generativeart.NewJulia(julia1, 40))
+	c.ToPNG("julia.png")
+}
diff --git a/julia.go b/julia.go
new file mode 100644
index 0000000..c80b6b9
--- /dev/null
+++ b/julia.go
@@ -0,0 +1,40 @@
+package generativeart
+
+import "math/cmplx"
+
+// GenFunc defines a func type used by julia set.
+type GenFunc func(complex128) complex128
+
+type julia struct {
+	fn   GenFunc
+	maxz float64
+}
+
+func NewJulia(formula GenFunc, maxz float64) *julia {
+	return &julia{
+		fn: formula,
+		maxz: maxz,
+	}
+}
+
+// Generative draws a julia set.
+func (j *julia)Generative(c *canva) {
+	n := len(c.opts.colorSchema)
+	if n > 255 {
+		n = 255
+	}
+
+	for i := 0; i <= c.width; i++ {
+		for k := 0; k <= c.height; k++ {
+			nit := 0
+			z := complex(float64(i)/float64(c.width)*2.0*c.yaixs-c.yaixs, float64(k)/float64(c.height)*2.0*c.yaixs-c.yaixs)
+
+			for cmplx.Abs(z) <= j.maxz && nit < c.opts.nIters {
+				z = j.fn(z)
+				nit += 1
+			}
+			idx := uint8(nit*255/c.opts.nIters) % uint8(n)
+			c.img.Set(i, k, c.opts.colorSchema[idx])
+		}
+	}
+}
\ No newline at end of file