gopl-Exercise1.5: Animated GIFs

本文主要用来记录Golang学习中，Animated GIFs的小节作业。

源码

// Copyright © 2016 Alan A. A. Donovan & Brian W. Kernighan.// License: https://creativecommons.org/licenses/by-nc-sa/4.0/// Run with "web" command-line argument for web server.// See page 13.//!+main// Lissajous generates GIF animations of random Lissajous figures.package mainimport (    "image"    "image/color"    "image/gif"    "io"    "math"    "math/rand"    "os")//!-main// Packages not needed by version in book.import (    "log"    "net/http"    "time")//!+main// var palette = []color.Color{color.White, color.Black}var palette = []color.Color{color.Black, color.RGBA{0x00, 0xff, 0x00, 0xff}}const (    // whiteIndex = 0 // first color in palette    // blackIndex = 1 // next color in palette    blackIndex = 0    greenIndex = 1)func main() {    //!-main    // The sequence of images is deterministic unless we seed    // the pseudo-random number generator using the current time.    // Thanks to Randall McPherson for pointing out the omission.    rand.Seed(time.Now().UTC().UnixNano())    if len(os.Args) > 1 && os.Args[1] == "web" {        //!+http        handler := func(w http.ResponseWriter, r *http.Request) {            lissajous(w)        }        http.HandleFunc("/", handler)        //!-http        log.Fatal(http.ListenAndServe("localhost:8000", nil))        return    }    //!+main    lissajous(os.Stdout)}func lissajous(out io.Writer) {    const (        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 {            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)            img.SetColorIndex(size+int(x*size+0.5), size+int(y*size+0.5),                greenIndex)        }        phase += 0.1        anim.Delay = append(anim.Delay, delay)        anim.Image = append(anim.Image, img)    }    gif.EncodeAll(out, &anim) // NOTE: ignoring encoding errors}//!-main

运行

$ go build$ ./lissajous.exe web

浏览器查看效果

在浏览器的地址栏中输入localhost:8000，并回车。

每次刷新网页，将看到不同样式的利萨茹曲线。

参考

1. 利萨茹曲线
2. golang-image-color-palette