add the black hole

README.md

@@ -32,6 +32,7 @@
     - [Circle Loop](#circle-loop)
     - [Circle Noise](#circle-noise)
     - [Julia Set](#julia-set)
+    - [Black Hole](#black-hole)
     - [Silk Sky](#silk-sky)
     - [Circle Move](#circle-move)
     - [Random Circle](#random-circle)
@@ -72,6 +73,7 @@ This package is still working in progress. More types would be added. Welcome an
 - Circle Move
 - Circle Noise
 - Yarn
+- Black Hole
 
 For these kinds of art, the package provides as many parameters to control the appearance.
 
@@ -109,6 +111,7 @@ NewDotsWave(dotsN int)
 NewCircleMove(circleNum int)
 NewCircleNoise(dotsN, colorMin, colorMax int)
 NewYarn(n int)
+NewBlackHole(circleN int, density, circleGap float64)
 ```
 
 ## Docs
@@ -445,6 +448,23 @@ func main() {
 
 ![](images/julia.png)
 
+### Black Hole
+
+```go
+func main() {
+	rand.Seed(time.Now().Unix())
+	c := generativeart.NewCanva(500, 500)
+	c.SetBackground(color.RGBA{R: 30, G: 30, B: 30, A: 255})
+	c.FillBackground()
+	c.SetLineWidth(1.0)
+	c.SetLineColor(common.Tomato)
+	c.Draw(arts.NewBlackHole(200, 400, 0.01))
+	c.ToPNG("blackhole.png")
+}
+```
+
+![](images/blackhole.png)
+
 ### Silk Sky
 
 ```go

arts/blackhole.go

@@ -0,0 +1,50 @@
+package arts
+
+import (
+	"github.com/fogleman/gg"
+	"github.com/jdxyw/generativeart"
+	"github.com/jdxyw/generativeart/common"
+	"math"
+)
+
+type blackHole struct {
+	circleN   int
+	density   float64
+	circleGap float64
+}
+
+// NewBlackHole returns a blackhole object.
+func NewBlackHole(circleN int, density, circleGap float64) *blackHole {
+	return &blackHole{
+		circleN:   circleN,
+		density:   density,
+		circleGap: circleGap,
+	}
+}
+
+// Generative draws a black hole image.
+func (b *blackHole) Generative(c *generativeart.Canva) {
+	ctex := gg.NewContextForRGBA(c.Img())
+	noise := common.NewPerlinNoise()
+	kMax := common.RandomRangeFloat64(0.5, 1)
+	ctex.SetLineWidth(0.4)
+	ctex.SetColor(c.Opts().LineColor())
+
+	for i := 0; i < b.circleN; i++ {
+		radius := float64(c.Width()/10) + float64(i)*0.05
+		k := kMax * math.Sqrt(float64(i)/float64(b.circleN))
+		noisiness := b.density * math.Pow(float64(i)/float64(b.circleN), 2)
+
+		for theta := 0.0; theta < 361; theta += 1.0 {
+			r1 := math.Cos(gg.Radians(theta)) + 1
+			r2 := math.Sin(gg.Radians(theta)) + 1
+			r := radius + noise.Noise3D(k*r1, k*r2, float64(i)*b.circleGap)*noisiness
+
+			x := float64(c.Width())/2 + r*math.Cos(gg.Radians(theta))
+			y := float64(c.Height()/2) + r*math.Sin(gg.Radians(theta))
+			ctex.LineTo(x, y)
+		}
+		ctex.Stroke()
+		ctex.ClearPath()
+	}
+}

docs/doc.md

@@ -32,6 +32,8 @@
 		- [parameters](#parameters-13)
 	- [Yarn](#yarn)
 		- [parameters](#parameters-14)
+	- [Black Hole](#black-hole)
+		- [parameters](#parameters-15)
 ## Color Circle 2
 
 `Color Circle2` is version 2 of `Color Circle`. It still draws the circle and point cloud.
@@ -225,10 +227,24 @@ cm := arts.NewCircleMove(1000)
 
 ### parameters
 
-- n: The number of curve.
+- n: The number of the curve.
 
 ```go
 y := arts.NewYarn(2000)
 ```
 
 ![](../images/yarn.png)
+
+## Black Hole
+
+### parameters
+
+- circleN: The number of the circle.
+- density: Control the density of the circle.
+- circleGap: Identify the gap between two circles.
+
+```go
+b := arts.NewBlackHole(200, 400, 0.01)
+```
+
+![](../images/blackhole.png)

example/example_blackhole.go

@@ -0,0 +1,21 @@
+package main
+
+import (
+	"github.com/jdxyw/generativeart"
+	"github.com/jdxyw/generativeart/arts"
+	"github.com/jdxyw/generativeart/common"
+	"image/color"
+	"math/rand"
+	"time"
+)
+
+func main() {
+	rand.Seed(time.Now().Unix())
+	c := generativeart.NewCanva(500, 500)
+	c.SetBackground(color.RGBA{R: 30, G: 30, B: 30, A: 255})
+	c.FillBackground()
+	c.SetLineWidth(1.0)
+	c.SetLineColor(common.Tomato)
+	c.Draw(arts.NewBlackHole(200, 400, 0.01))
+	c.ToPNG("blackhole.png")
+}