package main

import (
	"image"
	"image/color"
	"image/gif"
	"io"
	"math"
	"math/rand/v2"
	"os"
)

var palette = []color.Color{
	color.White,
	color.Black,
}

const (
	whiteIndex = iota
	blackIndex
)

func main() {
	lissajous(os.Stdout)
}

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}
	phase := 0.0

	for range nframes {
		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 {
			x := math.Sin(t)
			y := math.Sin(t*freq + phase)
			img.SetColorIndex(size+int(x*size+0.5), size+int(y*size+0.5), blackIndex)
		}

		phase += 0.1
		anim.Delay = append(anim.Delay, delay)
		anim.Image = append(anim.Image, img)
	}

	gif.EncodeAll(out, &anim)
}