a gift to 15.Aug moon

8-15 moon

// 8.15 project main.go
// generate a pic of moon
package main

import (
  "fmt"
  "image"
	"image/color"
	"image/draw"
	"image/png"
	"os"
)

func drawCircle(img draw.Image, x, y, radius int, fill color.Color) {
	// Algorithm taken from
	// http://en.wikipedia.org/wiki/Midpoint_circle_algorithm
	x0, y0 := x, y
	f := 1 - radius
	ddF_x, ddF_y := 1, -2*radius
	x, y = 0, radius

	img.Set(x0, y0+radius, fill)
	img.Set(x0, y0-radius, fill)
	img.Set(x0+radius, y0, fill)
	img.Set(x0-radius, y0, fill)

	for x < y {
		if f >= 0 {
			y--
			ddF_y += 2
			f += ddF_y
		}
		x++
		ddF_x += 2
		f += ddF_x
		img.Set(x0+x, y0+y, fill)
		img.Set(x0-x, y0+y, fill)
		img.Set(x0+x, y0-y, fill)
		img.Set(x0-x, y0-y, fill)
		img.Set(x0+y, y0+x, fill)
		img.Set(x0-y, y0+x, fill)
		img.Set(x0+y, y0-x, fill)
		img.Set(x0-y, y0-x, fill)
	}
}

func main() {
	fd, err := os.Create("15.png")
	if err != nil {
		fmt.Println("create file failed")
		return
	}
	defer fd.Close()

	img := image.NewRGBA(image.Rect(0, 0, 400, 300))
	draw.Draw(img, img.Bounds(), &image.Uniform{color.Black}, image.ZP, draw.Src)
	drawCircle(img, 100, 100, 50, color.White)
	png.Encode(fd, img)

	fmt.Println("Hello World!")
}