// Lissajous generates GIF animations of random Lissajous figures.
var palette = []color.Color{color.White, color.Black}
whiteIndex = 0 // first color in palette
blackIndex = 1 // next color in palette
func lissajous(out io.Writer) {
cycles = 5 // number of complete x oscillator revolutions
res = 0.001 // angular resolution
size = 100 // image canvas covers [-size..+size]
nframes = 64 // number of animation frames
delay = 8 // delay between frames in 10ms units
freq := rand.Float64() * 3.0 // relative frequency of y oscillator
anim := gif.GIF{LoopCount: nframes}
phase := 0.0 // phase difference
for i := 0; i < nframes; i++ {
rect := image.Rect(0, 0, 2*size+1, 2*size+1)
img := image.NewPaletted(rect, palette)
for t := 0.0; t < cycles*2*math.Pi; t += res {
y := math.Sin(t*freq + phase)
img.SetColorIndex(size+int(x*size+0.5), size+int(y*size+0.5),
anim.Delay = append(anim.Delay, delay)
anim.Image = append(anim.Image, img)
gif.EncodeAll(out, &anim) // NOTE: ignoring encoding errors