# [日常] Go语言圣经--浮点数习题

```// Surface computes an SVG rendering of a 3-D surface function.
package main

import (
"fmt"
"math"
"net/http"
"strconv"
)

var height,width float64 = 300 , 600
var     cells         float64= 100                 // number of grid cells
var     xyrange       float64= 30.0                // axis ranges (-xyrange..+xyrange)
var     xyscale       float64= width / 2 / xyrange // pixels per x or y unit
var     zscale        float64= height * 0.4        // pixels per z unit
var     angle         float64= math.Pi / 6         // angle of x, y axes (=30°)

var sin30, cos30 = math.Sin(angle), math.Cos(angle) // sin(30°), cos(30°)

func main() {

//http服务
http.HandleFunc("/",handle)
http.ListenAndServe("0.0.0.0:8000",nil)
}
func handle(w http.ResponseWriter,r *http.Request){
if err := r.ParseForm();err != nil{
return
}
//var height int
//var width  int
for k,v := range r.Form{
if k == "height"{
h, _ := strconv.ParseFloat(v[0],64)
if h>0 {height = h}
}
if k == "width"{
w, _ := strconv.ParseFloat(v[0],64)
if w>0 {width = w}
}
}
xyscale = width / 2 / xyrange
zscale = height * 0.4
fmt.Fprintf(w,"<svg xmlns='http://www.w3.org/2000/svg' "+
"style='stroke: #ff0000; fill: #0000ff; stroke-width: 0.7' "+
"width='%d' height='%d'>", width, height)
for i := 0; i < int(cells); i++ {
for j := 0; j < int(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) {
// Find point (x,y) at corner of cell (i,j).
x := xyrange * (float64(i)/cells - 0.5)
y := xyrange * (float64(j)/cells - 0.5)

// Compute surface height z.
z := f(x, y)

// Project (x,y,z) isometrically onto 2-D SVG canvas (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) // distance from (0,0)
return math.Sin(r) / r
}```

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