函数sin(r)/r的图形输出样例

package main
//根据一个三维曲面函数计算并生成svg
import (
	"fmt"
	"math"
	"net/http"
)

const (
	width, height = 600, 320 //以像素表示的画布大小
	cells         = 100 //网格单元的个数
	xyrange       = 30.0//坐标轴的范围 (-xyrange,xyrange)
	xyscale       = width / 2 / xyrange //x 或 y轴上每个单位长度的像素
	zscale        = height * 0.4 //z轴上每个单位长度的像素
	angle         = math.Pi / 6//x、y轴的角度 (=30°)
)

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

func main() {
	http.HandleFunc("/", drawSVG)
	http.ListenAndServe("localhost:8080", nil)
}

func drawSVG(w http.ResponseWriter, r *http.Request) {
	w.Header().Set("Content-type", "image/svg+xml")
	_, _ = fmt.Fprintf(w, "<svg xmlns='http://www.w3.org/2000/svg' "+
		"style='stroke:grey;fill:white;stroke-width:0.7' width='%d' height='%d'>\n",
		width, height)
	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) {
	//求出网格单元 (i,j)的顶点坐标(x,y)
	x := xyrange * (float64(i)/cells - 0.5)
	y := xyrange * (float64(j)/cells - 0.5)
	//计算曲面高度 z
	z := f(x, y)
	//将(x,y,z)等角投射到二维svg绘图平面上,坐标(sx,sy)
	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) //到(0,0)的距离
	return math.Sin(r)/r
}

访问浏览器 http://localhost:8080 ,浏览器会展示如下图形

3d表达sin(r)/r