1 files changed, 61 insertions, 0 deletions
diff --git a/lissajous.go b/lissajous.go
new file mode 100644
index 0000000..1d1ad70
--- /dev/null
+++ b/lissajous.go
@@ -0,0 +1,61 @@
+package lissajous
+
+import (
+	"image"
+	"image/color"
+	"image/gif"
+	"io"
+	"math"
+	"math/rand/v2"
+)
+
+var palette = []color.Color{
+	color.Black,
+	color.RGBA{0x00, 0xff, 0x00, 0xff},
+	color.RGBA{0xff, 0x00, 0x00, 0xff},
+	color.RGBA{0x00, 0x00, 0xff, 0xff},
+}
+
+const (
+	backgroundIndex = iota
+	foregroundIndex
+)
+
+func Lissajous(out io.Writer) {
+	const (
+		cycles  = 5
+		res     = 0.001
+		size    = 100
+		nframes = 64
+		delay   = 8
+	)
+
+	// Note that this generates the exact same random number per
+	// run of the program.
+	freq := rand.Float64() * 3.0
+	anim := gif.GIF{LoopCount: nframes}
+
+	for i := range nframes {
+		img := newImage(size, cycles, float64(i)/10, res, freq)
+
+		anim.Delay = append(anim.Delay, delay)
+		anim.Image = append(anim.Image, img)
+	}
+
+	gif.EncodeAll(out, &anim)
+}
+
+func newImage(size, cycles int, phase, res, freq float64) *image.Paletted {
+	rect := image.Rect(0, 0, 2*size+1, 2*size+1)
+	img := image.NewPaletted(rect, palette)
+
+	randIndex := 1 + uint8(rand.IntN(len(palette)-1))
+
+	for t := 0.0; t < float64(cycles)*2*math.Pi; t += res {
+		x := math.Sin(t)
+		y := math.Sin(t*freq + phase)
+		img.SetColorIndex(size+int(x*float64(size)+0.5), size+int(y*float64(size)+0.5), randIndex)
+	}
+
+	return img
+}