87 lines
2.0 KiB
Go
87 lines
2.0 KiB
Go
// Copyright © 2016 Alan A. A. Donovan & Brian W. Kernighan.
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// License: https://creativecommons.org/licenses/by-nc-sa/4.0/
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// Run with "web" command-line argument for web server.
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// See page 13.
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//!+main
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// Lissajous generates GIF animations of random Lissajous figures.
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package main
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import (
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"image"
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"image/color"
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"image/gif"
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"io"
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"math"
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"math/rand"
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"os"
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)
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//!-main
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// Packages not needed by version in book.
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import (
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"log"
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"net/http"
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"time"
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)
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//!+main
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var palette = []color.Color{color.White, color.Black}
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const (
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whiteIndex = 0 // first color in palette
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blackIndex = 1 // next color in palette
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)
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func main() {
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//!-main
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// The sequence of images is deterministic unless we seed
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// the pseudo-random number generator using the current time.
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// Thanks to Randall McPherson for pointing out the omission.
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rand.Seed(time.Now().UTC().UnixNano())
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if len(os.Args) > 1 && os.Args[1] == "web" {
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//!+http
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handler := func(w http.ResponseWriter, r *http.Request) {
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lissajous(w)
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}
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http.HandleFunc("/", handler)
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//!-http
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log.Fatal(http.ListenAndServe("localhost:8000", nil))
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return
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}
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//!+main
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lissajous(os.Stdout)
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}
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func lissajous(out io.Writer) {
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const (
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cycles = 5 // number of complete x oscillator revolutions
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res = 0.001 // angular resolution
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size = 100 // image canvas covers [-size..+size]
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nframes = 64 // number of animation frames
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delay = 8 // delay between frames in 10ms units
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)
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freq := rand.Float64() * 3.0 // relative frequency of y oscillator
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anim := gif.GIF{LoopCount: nframes}
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phase := 0.0 // phase difference
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for i := 0; i < nframes; i++ {
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rect := image.Rect(0, 0, 2*size+1, 2*size+1)
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img := image.NewPaletted(rect, palette)
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for t := 0.0; t < cycles*2*math.Pi; t += res {
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x := math.Sin(t)
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y := math.Sin(t*freq + phase)
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img.SetColorIndex(size+int(x*size+0.5), size+int(y*size+0.5),
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blackIndex)
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}
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phase += 0.1
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anim.Delay = append(anim.Delay, delay)
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anim.Image = append(anim.Image, img)
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}
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gif.EncodeAll(out, &anim) // NOTE: ignoring encoding errors
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}
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//!-main
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