63 lines
1.7 KiB
Go
63 lines
1.7 KiB
Go
// Copyright © 2016 Alan A. A. Donovan & Brian W. Kernighan.
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// License: https://creativecommons.org/licenses/by-nc-sa/4.0/
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// See page 58.
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//!+
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// Surface computes an SVG rendering of a 3-D surface function.
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package main
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import (
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"fmt"
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"math"
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)
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const (
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width, height = 600, 320 // canvas size in pixels
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cells = 100 // number of grid cells
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xyrange = 30.0 // axis ranges (-xyrange..+xyrange)
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xyscale = width / 2 / xyrange // pixels per x or y unit
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zscale = height * 0.4 // pixels per z unit
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angle = math.Pi / 6 // angle of x, y axes (=30°)
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)
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var sin30, cos30 = math.Sin(angle), math.Cos(angle) // sin(30°), cos(30°)
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func main() {
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fmt.Printf("<svg xmlns='http://www.w3.org/2000/svg' "+
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"style='stroke: grey; fill: white; stroke-width: 0.7' "+
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"width='%d' height='%d'>", width, height)
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for i := 0; i < cells; i++ {
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for j := 0; j < cells; j++ {
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ax, ay := corner(i+1, j)
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bx, by := corner(i, j)
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cx, cy := corner(i, j+1)
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dx, dy := corner(i+1, j+1)
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fmt.Printf("<polygon points='%g,%g %g,%g %g,%g %g,%g'/>\n",
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ax, ay, bx, by, cx, cy, dx, dy)
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}
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}
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fmt.Println("</svg>")
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}
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func corner(i, j int) (float64, float64) {
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// Find point (x,y) at corner of cell (i,j).
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x := xyrange * (float64(i)/cells - 0.5)
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y := xyrange * (float64(j)/cells - 0.5)
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// Compute surface height z.
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z := f(x, y)
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// Project (x,y,z) isometrically onto 2-D SVG canvas (sx,sy).
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sx := width/2 + (x-y)*cos30*xyscale
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sy := height/2 + (x+y)*sin30*xyscale - z*zscale
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return sx, sy
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}
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func f(x, y float64) float64 {
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r := math.Hypot(x, y) // distance from (0,0)
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return math.Sin(r) / r
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}
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//!-
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