コッホ雪片

snowflake.js

/**
 * コッホ雪片
 */

// 設定
/*==========================*/
// 初期座標
var a = {x: 10, y: 580};
var b = {x: 1990, y: 580};
// 描画サイズ
var size = {width: 2000, height: 2300};
// 描画色
var style = "rgba(0, 0, 255, 0.5)";
// 再帰回数
var t = 10;
/*==========================*/

var c = {
  x:   ((a.x - b.x) + Math.sqrt(3) * (a.y - b.y)) / 2 + b.x,
  y: - (Math.sqrt(3) * (a.x - b.x) - (a.y - b.y)) / 2 + b.y
};

var Canvas = require("canvas"),
    fs = require("fs");

var canvas = new Canvas(size.width, size.height),
    ctx = canvas.getContext("2d");

ctx.fillStyle = "rgb(255,255,255)";
ctx.fillRect(0, 0, size.width, size.height);

var points = koch(t, [a, b, c, a]);
points.reduce(function (a, b) {
  stroke(a, b, style);
  return b;
});

// write out
var out_stream = fs.createWriteStream("snowflake.png");
canvas.pngStream().pipe(out_stream);

function koch(t, points) {
  if (t-- === 0) return points;

  var res = [a];
  points.reduce(function (a, b) {
    var c = {}, d = {}, e = {};
    e.x = b.x - (b.x - a.x) / 3;
    e.y = b.y - (b.y - a.y) / 3;
    d.x = b.x - (b.x - a.x) / 3 * 2;
    d.y = b.y - (b.y - a.y) / 3 * 2;
    dx = (a.x - d.x);
    dy = (a.y - d.y);
    c.x = - (dx + Math.sqrt(3) * dy) / 2 + d.x;
    c.y = (Math.sqrt(3) * dx - dy) / 2 + d.y;
    res.push(d, c, e, b);
    return b;
  });

  return koch(t, res);
}

function stroke(a, b, style) {
  ctx.beginPath();
  ctx.moveTo(a.x, a.y);
  ctx.lineTo(b.x, b.y);
  ctx.strokeStyle = style;
  ctx.stroke();
}