add point ribbon

README.md

@@ -161,6 +161,37 @@ func main() {
 
 ![](images/julia.png)
 
+### Silk Sky
+
+```go
+func main() {
+	rand.Seed(time.Now().Unix())
+	c := generativeart.NewCanva(600, 600)
+	c.SetAlpha(10)
+	c.Draw(generativeart.NewSilkSky(15, 5))
+	c.ToPNG("silksky.png")
+}
+```
+
+![](images/silksky.png)
+
+### Point Ribbon
+
+```go
+func main() {
+	rand.Seed(time.Now().Unix())
+	c := generativeart.NewCanva(500, 500)
+	c.SetBackground(generativeart.Lavender)
+	c.SetLineWidth(2)
+	c.SetIterations(150000)
+	c.FillBackground()
+	c.Draw(generativeart.NewPointRibbon(50))
+	c.ToPNG("pointribbon.png")
+}
+```
+
+![](images/pointribbon.png)
+
 ### Swirl
 
 ```go
@@ -195,20 +226,6 @@ func main() {
 
 ![](images/circleline.png)
 
-### Silk Sky
-
-```go
-func main() {
-	rand.Seed(time.Now().Unix())
-	c := generativeart.NewCanva(600, 600)
-	c.SetAlpha(10)
-	c.Draw(generativeart.NewSilkSky(15, 5))
-	c.ToPNG("silksky.png")
-}
-```
-
-![](images/silksky.png)
-
 ### Maze
 
 ```go
@@ -268,3 +285,4 @@ Thanks for the following sites and repos, I got lots of ideas, inspiration, code
 - http://blog.dragonlab.de/2015/03/generative-art-week-1
 - https://editor.p5js.org/kenekk1/sketches/Ly-5XYvKX
 - http://paulbourke.net/fractals/peterdejong/
+- https://editor.p5js.org/kenekk1/sketches/O44Dln5oo

color.go

@@ -22,6 +22,7 @@ var (
 	Orange           = color.RGBA{0xFF, 0xA5, 0x00, 0xFF}
 	Black            = color.RGBA{0x00, 0x00, 0x00, 0xFF}
 	White            = color.RGBA{0xFF, 0xFF, 0xFF, 0xFF}
+	LightGray        = color.RGBA{200, 200, 200, 255}
 	Outdoors         = []color.RGBA{
 		{67, 110, 165, 255},
 		{47, 76, 114, 255},

example/example_pointribbon.go

@@ -0,0 +1,18 @@
+package main
+
+import (
+	"github.com/jdxyw/generativeart"
+	"math/rand"
+	"time"
+)
+
+func main() {
+	rand.Seed(time.Now().Unix())
+	c := generativeart.NewCanva(500, 500)
+	c.SetBackground(generativeart.Lavender)
+	c.SetLineWidth(2)
+	c.SetIterations(150000)
+	c.FillBackground()
+	c.Draw(generativeart.NewPointRibbon(50))
+	c.ToPNG("pointribbon.png")
+}

pointRibbon.go

@@ -0,0 +1,36 @@
+package generativeart
+
+import (
+	"github.com/fogleman/gg"
+	"math"
+)
+
+type pointRibbon struct {
+	r float64
+}
+
+// NewPointRibbon returns a pointRibbon object.
+func NewPointRibbon(r float64) *pointRibbon {
+	return &pointRibbon{
+		r: r,
+	}
+}
+
+// Generative draws a point ribbon image.
+// TODO: make the point as parameters.
+func (s *pointRibbon) Generative(c *canva) {
+	ctex := gg.NewContextForRGBA(c.img)
+	ctex.SetLineWidth(c.opts.lineWidth)
+
+	var t float64
+	var dt = 0.0001
+	for i := 0; i < c.opts.nIters; i++ {
+		delta := 2.0*s.r*math.Cos(4.0*dt*t) + s.r*math.Cos(t)
+		ctex.SetRGBA255(int(delta), int(2*s.r*math.Sin(t)-s.r*math.Cos(3*dt*t)), 100, 10)
+		ctex.DrawPoint(2*s.r*math.Sin(2*t*dt)+s.r*math.Cos(t*dt)+float64(c.width/2),
+			2*s.r*math.Sin(t*dt)-s.r*math.Sin(5*t)+float64(c.height/2), 1.0)
+		ctex.Stroke()
+		t += 0.01
+		dt += 0.1
+	}
+}

utils_test.go

@@ -17,13 +17,13 @@ func TestDistance(t *testing.T) {
 		args args
 		want float64
 	}{
-		{name: "testcase1", args: args{x1:0, y1:0, x2:0, y2:0}, want: 0},
-		{name: "testcase2", args: args{x1:0, y1:3, x2:4, y2:0}, want: 5},
-		{name: "testcase3", args: args{x1:1, y1:1, x2:0, y2:0}, want: 1.414213562},
+		{name: "testcase1", args: args{x1: 0, y1: 0, x2: 0, y2: 0}, want: 0},
+		{name: "testcase2", args: args{x1: 0, y1: 3, x2: 4, y2: 0}, want: 5},
+		{name: "testcase3", args: args{x1: 1, y1: 1, x2: 0, y2: 0}, want: 1.414213562},
 	}
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
-			if got := Distance(tt.args.x1, tt.args.y1, tt.args.x2, tt.args.y2); math.Abs(got-tt.want)>0.00001 {
+			if got := Distance(tt.args.x1, tt.args.y1, tt.args.x2, tt.args.y2); math.Abs(got-tt.want) > 0.00001 {
 				t.Errorf("Distance() = %v, want %v", got, tt.want)
 			}
 		})