add silk sky

example/example_silksky.go

@@ -0,0 +1,15 @@
+package main
+
+import (
+	"generativeart"
+	"math/rand"
+	"time"
+)
+
+func main() {
+	rand.Seed(time.Now().Unix())
+	c := generativeart.NewCanva(600, 600, 1, 1)
+	c.SetAlpha(10)
+	c.Draw(generativeart.NewSilkSky(15, 5))
+	c.ToPNG("silksky.png")
+}

silksky.go

@@ -0,0 +1,47 @@
+package generativeart
+
+import (
+	"github.com/fogleman/gg"
+	"math/rand"
+)
+
+type silkSky struct {
+	circleNum int
+	sunRadius float64
+}
+
+// NewSilkSky returns a silkSky object.
+func NewSilkSky(circleNum int, sunRadius float64) *silkSky {
+	return &silkSky{
+		circleNum: circleNum,
+		sunRadius: sunRadius,
+	}
+}
+
+// Generative draws a silk sky image.
+func (s *silkSky) Generative(c *canva) {
+	ctex := gg.NewContextForRGBA(c.img)
+	xm := float64(rand.Intn(c.width/5)) + float64(c.width*4/5-c.width/5)
+	ym := float64(rand.Intn(c.height/5))+ float64(c.height*4/5-c.height/5)
+
+	mh := s.circleNum*2 + 2
+	ms := s.circleNum*2 + 50
+	mv := 100
+
+	for i := 0; i < s.circleNum; i++ {
+		for j := 0; j < s.circleNum; j++ {
+			hsv := HSV{
+				H: s.circleNum + j,
+				S: i + 50,
+				V: 70,
+			}
+			rgba := hsv.ToRGB(mh, ms, mv)
+			xn := (float64(i) + 0.5) * float64(c.width) / float64(s.circleNum)
+			yn := (float64(j) + 0.5) * float64(c.height) / float64(s.circleNum)
+			ctex.SetRGBA255(int(rgba.R), int(rgba.G), int(rgba.B), c.opts.alpha)
+			r := Distance(xn, yn, xm, ym)
+			ctex.DrawEllipse(xn, yn, r-s.sunRadius/2, r-s.sunRadius/2)
+			ctex.Fill()
+		}
+	}
+}

utils.go

@@ -1,6 +1,82 @@
 package generativeart
 
-import "math"
+import (
+	"image/color"
+	"math"
+)
+
+type HSV struct {
+	H, S, V int
+}
+
+func (hs HSV) ToRGB(mh, ms, mv int) color.RGBA {
+	if hs.H > mh {
+		hs.H = mh
+	}
+
+	if hs.S > ms {
+		hs.S = ms
+	}
+
+	if hs.V > mv {
+		hs.V = mv
+	}
+
+	h, s, v := float64(hs.H)/float64(mh), float64(hs.S)/float64(ms), float64(hs.V)/float64(mv)
+
+	var r, g, b float64
+	if s == 0 { //HSV from 0 to 1
+		r = v * 255
+		g = v * 255
+		b = v * 255
+	} else {
+		h = h * 6
+		if h == 6 {
+			h = 0
+		} //H must be < 1
+		i := math.Floor(h) //Or ... var_i = floor( var_h )
+		v1 := v * (1 - s)
+		v2 := v * (1 - s*(h-i))
+		v3 := v * (1 - s*(1-(h-i)))
+
+		if i == 0 {
+			r = v
+			g = v3
+			b = v1
+		} else if i == 1 {
+			r = v2
+			g = v
+			b = v1
+		} else if i == 2 {
+			r = v1
+			g = v
+			b = v3
+		} else if i == 3 {
+			r = v1
+			g = v2
+			b = v
+		} else if i == 4 {
+			r = v3
+			g = v1
+			b = v
+		} else {
+			r = v
+			g = v1
+			b = v2
+		}
+
+		r = r * 255 //RGB results from 0 to 255
+		g = g * 255
+		b = b * 255
+	}
+	rgb := color.RGBA{
+		R: uint8(r),
+		G: uint8(g),
+		B: uint8(b),
+		A: 0,
+	}
+	return rgb
+}
 
 func ConvertCartesianToPixel(x, y, xaixs, yaixs float64, h, w int) (int, int) {
 	xr, yr := x/xaixs, y/yaixs