surface

README.md

@@ -22,4 +22,5 @@
 | 18    | floatToInt       | 浮点数损失    |
 | 19    | runeLiteral      | 文字符号     |
 | 20    | float            | 浮点数      |
-| 21    | InfNaN           | 无穷非数     |
+| 21    | InfNaN           | 无穷非数     |
+| 22    | surface          | 三维曲面函数图像 |

surface/surface.go

@@ -0,0 +1,45 @@
+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 := 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) {
+	x := xyrange * (float64(i)/cells - 0.5)
+	y := xyrange * (float64(i)/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)
+}