ch3/ch3-02

[giscus[bot]]

ch3/ch3-02

中文版

https://golang-china.github.io/gopl-zh/ch3/ch3-02.html

[cicospui]

纯新手，感觉练习好难啊！有没有答案什么的

[Bibooo25730]

l练个毛线哦

[xq-120]

3.4

func main() {
	http.HandleFunc("/", handler)
	err := http.ListenAndServe("localhost:8080", nil)
	log.Fatal(err)
}

func handler(w http.ResponseWriter, r *http.Request) {
	//不加Content-Type，浏览器显示的是svg文件内容，而不是解析显示为图片。
	w.Header().Set("Content-Type", "image/svg+xml")

	err := r.ParseForm()
	if err != nil {
		log.Print(err)
	}
	form := r.Form

	wd := 0
	wdQuery := form["width"]
	if len(wdQuery) > 0 { //必须判断数组是否为空，否则越界崩溃
		wdStr := wdQuery[0]
		wd, err = strconv.Atoi(wdStr)
		if err != nil {
			log.Print(err)
		}
	}

	ht := 0
	htQuery := form["height"]
	if len(htQuery) > 0 { //必须判断数组是否为空，否则越界崩溃
		htStr := htQuery[0]
		ht, err = strconv.Atoi(htStr)
		if err != nil {
			log.Print(err)
		}
	}

	stroke := ""
	strokeQuery := form["stroke"]
	if len(strokeQuery) > 0 { //必须判断数组是否为空，否则越界崩溃
		stroke = strokeQuery[0]
	}

	surface(w, wd, ht, stroke)
}

func surface(w io.Writer, wd int, ht int, stroke string) {
	if wd <= 0 {
		wd = width
	}
	if ht <= 0 {
		ht = height
	}
	if len(stroke) == 0 {
		stroke = "grey"
	}
	fmt.Fprintf(w, "<svg xmlns='http://www.w3.org/2000/svg' "+
		"style='stroke: %s; fill: white; stroke-width: 0.7' "+
		"width='%d' height='%d'>", stroke, wd, ht)
	for i := 0; i < cells; i++ {
		for j := 0; j < cells; j++ {
			ax, ay := corner(i+1, j)
			bx, by := corner(i, j)
			cx, cy := corner(i, j+1)
			dx, dy := corner(i+1, j+1)
			fmt.Fprintf(w, "<polygon points='%g,%g %g,%g %g,%g %g,%g'/>\n",
				ax, ay, bx, by, cx, cy, dx, dy)
		}
	}
	fmt.Fprintf(w, "</svg>")
}

func corner(i, j int) (float64, float64) {
	x := xyrange * (float64(i)/cells - 0.5)
	y := xyrange * (float64(j)/cells - 0.5)
	z := f(x, y)

	sx := width/2 + (x-y)*cos30*xyscale
	sy := height/2 + (x+y)*sin30*xyscale - z*zscale
	return sx, sy
}

func f(x, y float64) float64 {
	r := math.Hypot(x, y)
	return math.Sin(r) / r
}

[liudeihao]

练习3.2：
因为需要根据z值调整颜色，所以让corner函数把z值也返回。
然后根据z的大小调整颜色。

package main

import (
	"fmt"
	"math"
)

const (
	width, height = 600, 320
	cells         = 100
	xyrange       = 30.0
	xyscale       = width / 2 / xyrange
	zscale        = height * 0.4
	angle         = math.Pi / 6
)

var sin30, cos30 = math.Sin(angle), math.Cos(angle)

func main() {
	fmt.Printf("<svg xmlns='http://www.w3.org/2000/svg' "+
		"style='stroke: grey; fill: white; stroke-width: 0.7' "+
		"width='%d' height='%d'>", width, height)

	for i := 0; i < cells; i++ {
		for j := 0; j < cells; j++ {
			ax, ay, az := corner(i+1, j)
			bx, by, bz := corner(i, j)
			cx, cy, cz := corner(i, j+1)
			dx, dy, dz := corner(i+1, j+1)
			
			avgZ := (az + bz + cz + dz) / 4
			maxZ := 1.
			minZ := -1 / math.Pi
			
			relativeZ := int32(math.Round((avgZ - minZ) / (maxZ - minZ) * 255))
			color := (relativeZ << 16) | (255 - relativeZ)
			fmt.Printf("<polygon points='%g,%g %g,%g %g,%g %g,%g' fill='#%6x'/>\n",
				ax, ay, bx, by, cx, cy, dx, dy, color)
		}
	}
	fmt.Println("</svg>\n")
}

func corner(i, j int) (float64, float64, float64) {
	x := xyrange * (float64(i)/cells - 0.5)
	y := xyrange * (float64(j)/cells - 0.5)
	z := f(x, y)
	sx := width/2 + (x-y)*cos30*xyscale
	sy := height/2 + (x+y)*sin30*xyscale - z*zscale
	return sx, sy, z
}

func f(x, y float64) float64 {
	r := math.Hypot(x, y)
	return math.Sin(r) / r
}