リサジュー図形の描画

2017-11-25 Go

Go言語（Golang）のバイブル「プログラミング言語Go」の「1.4 GIFアニメーション」の練習問題1.6 にある、リサジュー図形をカラフルに生成するプログラムを作成しました。結構シンプルに作成することができます。

// Copyright © 2016 Alan A. A. Donovan & Brian W. Kernighan.
// License: https://creativecommons.org/licenses/by-nc-sa/4.0/
// このプログラムは Alan A. A. Donovan & Brian W. Kernighan による gopl.io/ch1/lissajous を
// 改変したものです。

package main

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

import (
        "log"
        "net/http"
        "time"
)

var palette = []color.Color{color.White, color.Black,
        color.RGBA{0xff, 0x0, 0x0, 0xff}, color.RGBA{0x0, 0xff, 0x0, 0xff},
        color.RGBA{0x0, 0x0, 0xff, 0xff}, color.RGBA{0xff, 0xff, 0x0, 0xff}}

const (
        whiteIndex  = 0 // first color in palette
        blackIndex  = 1 // next color in palette
        redIndex    = 2 // 3rd color in palette
        greenIndex  = 3 // 4th color in palette
        blueIndex   = 4 // 5th color in palette
        yellowIndex = 5 // 6th color in palette
)

func main() {
        rand.Seed(time.Now().UTC().UnixNano())

        if len(os.Args) &gt; 1 &amp;&amp; os.Args[1] == "web" {
                handler := func(w http.ResponseWriter, r *http.Request) {
                        lissajous(w)
                }
                http.HandleFunc("/", handler)
                log.Fatal(http.ListenAndServe("localhost:8000", nil))
                return
        }
        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
        var nowColorIndex uint8
        for i := 0; i &lt; nframes; i++ {
                rect := image.Rect(0, 0, 2*size+1, 2*size+1)
                img := image.NewPaletted(rect, palette)
                preX, preY := 0.0, 0.0
                for t := 0.0; t &lt; cycles*2*math.Pi; t += res {
                        x := math.Sin(t)
                        y := math.Sin(t*freq + phase)

                        if preX &lt;= x {
                                if preY &lt;= y {
                                        nowColorIndex = redIndex
                                } else {
                                        nowColorIndex = greenIndex
                                }
                        } else {
                                if preY &lt;= y {
                                        nowColorIndex = blueIndex
                                } else {
                                        nowColorIndex = yellowIndex
                                }
                        }
                        preX, preY = x, y

                        img.SetColorIndex(size+int(x*size+0.5), size+int(y*size+0.5),
                                nowColorIndex)
                }
                phase += 0.1
                anim.Delay = append(anim.Delay, delay)
                anim.Image = append(anim.Image, img)
        }
        gif.EncodeAll(out, &amp;anim) // NOTE: ignoring encoding errors
}

// License: https://creativecommons.org/licenses/by-nc-sa/4.0/

// このプログラムは Alan A. A. Donovan & Brian W. Kernighan による gopl.io/ch1/lissajous を

// 改変したものです。

package main

import (

"image"

"image/color"

"image/gif"

"io"

"math"

"math/rand"

"os"

)

import (

"log"

"net/http"

"time"

)

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

color.RGBA{0xff, 0x0, 0x0, 0xff}, color.RGBA{0x0, 0xff, 0x0, 0xff},

color.RGBA{0x0, 0x0, 0xff, 0xff}, color.RGBA{0xff, 0xff, 0x0, 0xff}}

const (

whiteIndex = 0 // first color in palette

blackIndex = 1 // next color in palette

redIndex = 2 // 3rd color in palette

greenIndex = 3 // 4th color in palette

blueIndex = 4 // 5th color in palette

yellowIndex = 5 // 6th color in palette

)

func main() {

rand.Seed(time.Now().UTC().UnixNano())

if len(os.Args) > 1 && os.Args[1] == "web" {

handler := func(w http.ResponseWriter, r *http.Request) {

lissajous(w)

}

http.HandleFunc("/", handler)

log.Fatal(http.ListenAndServe("localhost:8000", nil))

return

}

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

var nowColorIndex uint8

for i := 0; i < nframes; i++ {

rect := image.Rect(0, 0, 2*size+1, 2*size+1)

img := image.NewPaletted(rect, palette)

preX, preY := 0.0, 0.0

for t := 0.0; t < cycles*2*math.Pi; t += res {

x := math.Sin(t)

y := math.Sin(t*freq + phase)

if preX <= x {

if preY <= y {

nowColorIndex = redIndex

} else {

nowColorIndex = greenIndex

}

} else {

if preY <= y {

nowColorIndex = blueIndex

} else {

nowColorIndex = yellowIndex

}

preX, preY = x, y

img.SetColorIndex(size+int(x*size+0.5), size+int(y*size+0.5),

nowColorIndex)

}

phase += 0.1

anim.Delay = append(anim.Delay, delay)

anim.Image = append(anim.Image, img)

}

gif.EncodeAll(out, &anim) // NOTE: ignoring encoding errors

}

このプログラムを「main.go」という名前で保存して、以下のコマンドを実行することで、リサジュー図形の画像を生成することができます。

$ go run main.go > out.gif

1	$ go run main.go > out.gif

参考文献

「プログラミング言語Go」 Alan A.A. Donovan (著),‎ Brian W. Kernighan (著),‎ 柴田芳樹 (翻訳)