Go语言圣经习题练习_1.4. GIF动画

练习 1.5： 修改前面的Lissajous程序里的调色板，由黑色改为绿色。我们可以用color.RGBA{0xRR, 0xGG, 0xBB, 0xff}来得到#RRGGBB这个色值，三个十六进制的字符串分别代表红、绿、蓝像素。

练习 1.6： 修改Lissajous程序，修改其调色板来生成更丰富的颜色，然后修改SetColorIndex的第三个参数，看看显示结果吧。

package main

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

//定义调色板
var palette = []color.Color{ color.RGBA{255,255,255,math.MaxUint8}, color.Black, color.RGBA{0,0,128,math.MaxUint8},color.RGBA{30,144,255,math.MaxUint8},color.RGBA{72,61,139,math.MaxUint8},color.RGBA{255,0,255,math.MaxUint8},color.RGBA{124,252,0,math.MaxUint8}}

const (
        whiteIndex = 0 // first color in palette
        blackIndex = 1 // next color in palette
        greenIndex = 2 // next color in palette 定义新的颜色
)

func 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 = 128    // 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,c := 0,1; 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),uint8(c)) //使用新的颜色
                }
                c ++ //修改颜色选择
                if c >= len(palette) {
    　　　　　　　　　　  c = 1
                }
                phase += 0.1
                anim.Delay = append(anim.Delay, delay)
                anim.Image = append(anim.Image, img)
        }
        gif.EncodeAll(out, &anim) // NOTE: ignoring encoding errors
}