mirror of
https://github.com/gopl-zh/gopl-zh.github.com.git
synced 2024-12-27 15:26:20 +00:00
63 lines
1.7 KiB
Go
63 lines
1.7 KiB
Go
// Copyright © 2016 Alan A. A. Donovan & Brian W. Kernighan.
|
|
// License: https://creativecommons.org/licenses/by-nc-sa/4.0/
|
|
|
|
// See page 58.
|
|
//!+
|
|
|
|
// Surface computes an SVG rendering of a 3-D surface function.
|
|
package main
|
|
|
|
import (
|
|
"fmt"
|
|
"math"
|
|
)
|
|
|
|
const (
|
|
width, height = 600, 320 // canvas size in pixels
|
|
cells = 100 // number of grid cells
|
|
xyrange = 30.0 // axis ranges (-xyrange..+xyrange)
|
|
xyscale = width / 2 / xyrange // pixels per x or y unit
|
|
zscale = height * 0.4 // pixels per z unit
|
|
angle = math.Pi / 6 // angle of x, y axes (=30°)
|
|
)
|
|
|
|
var sin30, cos30 = math.Sin(angle), math.Cos(angle) // sin(30°), cos(30°)
|
|
|
|
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 := corner(i+1, j)
|
|
bx, by := corner(i, j)
|
|
cx, cy := corner(i, j+1)
|
|
dx, dy := corner(i+1, j+1)
|
|
fmt.Printf("<polygon points='%g,%g %g,%g %g,%g %g,%g'/>\n",
|
|
ax, ay, bx, by, cx, cy, dx, dy)
|
|
}
|
|
}
|
|
fmt.Println("</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
|
|
}
|
|
|
|
//!-
|