add spiral square

example/example_spiralsquare.go

@@ -0,0 +1,20 @@
+package main
+
+import (
+	"generativeart"
+	"math/rand"
+	"time"
+)
+
+func main() {
+	rand.Seed(time.Now().Unix())
+	c := generativeart.NewCanva(500, 500, 2, 2)
+	c.SetBackground(generativeart.MistyRose)
+	c.SetLineWidth(10)
+	c.SetLineColor(generativeart.Orange)
+	c.SetColorSchema(generativeart.Plasma)
+	c.SetForeground(generativeart.Tomato)
+	c.FillBackground()
+	c.Draw(generativeart.NewSpiralSquare(40, 400, 0.05, true))
+	c.ToPNG("spiralsquare.png")
+}

spiralsquare.go

@@ -0,0 +1,61 @@
+package generativeart
+
+import (
+	"github.com/fogleman/gg"
+	"math/rand"
+)
+
+type spiralSquare struct {
+	squareNum int
+	decay     float64
+	rectSide  float64
+	randColor bool
+}
+
+// NewSpiralSquare returns a spiralSquare object.
+func NewSpiralSquare(squareNum int, rectSide, decay float64, randColor bool) *spiralSquare {
+	return &spiralSquare{
+		squareNum: squareNum,
+		decay:     decay,
+		rectSide:  rectSide,
+		randColor: randColor,
+	}
+}
+
+// Generative draws a spiral square images.
+func (s *spiralSquare) Generative(c *canva) {
+	ctex := gg.NewContextForRGBA(c.img)
+
+	sl := s.rectSide
+	theta := rand.Intn(360) + 1
+	for i := 0; i < s.squareNum; i++ {
+		ctex.Push()
+		ctex.Translate(float64(c.width/2), float64(c.height/2))
+		ctex.Rotate(gg.Radians(float64(theta * (i + 1))))
+
+		ctex.Scale(sl, sl)
+
+		ctex.LineTo(-0.5, 0.5)
+		ctex.LineTo(0.5, 0.5)
+		ctex.LineTo(0.5, -0.5)
+		ctex.LineTo(-0.5, -0.5)
+		ctex.LineTo(-0.5, 0.5)
+
+		ctex.SetLineWidth(c.opts.lineWidth)
+		ctex.SetColor(c.opts.lineColor)
+		ctex.StrokePreserve()
+
+		if s.randColor {
+			ctex.SetColor(c.opts.colorSchema[rand.Intn(len(c.opts.colorSchema))])
+		} else {
+			ctex.SetColor(c.opts.foreground)
+		}
+		ctex.Fill()
+		ctex.Pop()
+		sl = sl - s.decay*s.rectSide
+
+		if sl < 0 {
+			return
+		}
+	}
+}