1.常量声明的值必须是一个数字值、字符串或者一个固定的boolean值。 2.常量声明和变量声明一般都会出现在包级别 3.[]color.Color{...}生成的是一个slice切片和gif.GIF{...}生成的是一个struct结构体这两个表达式就是我们说的复合声明 4.struct是一组值或者叫字段的集合,不同的类型集合在一个struct可以让我们以一个统一的单元进行处理,struct内部的变量可以以一个点(.)来进行访问 5.import了一个包路径包含有多个单词的package时,比如image/color(image和color两个单词),通常我们只需要用最后那个单词表示这个包就可以
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。
package main
import (
"image"
"image/color"
"image/gif"
"io"
"math"
"math/rand"
"os"
"time"
)
//定义一个slice切片变量,复合声明
var palette = []color.Color{color.White, color.RGBA{0, 255, 68, 255}}
//声明一组常量
const (
whiteIndex = 0
blackIndex = 1
)
func main() {
rand.Seed(time.Now().UTC().UnixNano())
lissajous(os.Stdout)
}
//定义函数
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)
}
phase += 0.1
anim.Delay = append(anim.Delay, delay)
anim.Image = append(anim.Image, img)
}
gif.EncodeAll(out, &anim) // NOTE: ignoring encoding errors
}
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"
"time"
)
//定义一个slice切片变量,复合声明
var palette = []color.Color{color.White, color.RGBA{0, 255, 68, 255},color.RGBA{26, 0, 255, 255}}
//声明一组常量
const (
whiteIndex = 0
blackIndex = 1
)
func main() {
rand.Seed(time.Now().UTC().UnixNano())
lissajous(os.Stdout)
}
//定义函数
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)
}
phase += 0.1
anim.Delay = append(anim.Delay, delay)
anim.Image = append(anim.Image, img)
}
gif.EncodeAll(out, &anim) // NOTE: ignoring encoding errors
}