mirror of
https://github.com/gopl-zh/gopl-zh.github.com.git
synced 2024-11-10 00:13:43 +00:00
87 lines
2.0 KiB
Go
87 lines
2.0 KiB
Go
// 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 main
|
|
|
|
import (
|
|
"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}
|
|
|
|
const (
|
|
whiteIndex = 0 // first color in palette
|
|
blackIndex = 1 // next color in palette
|
|
)
|
|
|
|
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)
|
|
}
|
|
phase += 0.1
|
|
anim.Delay = append(anim.Delay, delay)
|
|
anim.Image = append(anim.Image, img)
|
|
}
|
|
gif.EncodeAll(out, &anim) // NOTE: ignoring encoding errors
|
|
}
|
|
|
|
//!-main
|