ジュリア集合を描く

juliaSet.js

let gridScale = 2.1;
let border = 2.7;
let maxCount = 150;

function getRealPart(x) {
  let rp = -1/2 + 1.0 * x / width;
  let s = height / width;
  return rp * gridScale/s;
}

function getImaginaryPart(y) {
  let ip = 1/2 - 1.0 * y / height;
  return ip * gridScale;
}

function drawJuliaSet(ca, cb) {
  for (let y = 0; y <= height; y++)
    {
      for(let x = 0; x <= width; x++)
        {
          // z = a + bi
          let a = getRealPart(x);
          let b = getImaginaryPart(y);

          let count = 0;
          while(dist(a,b,0,0) < border && count < maxCount)
            {
              // z -> z + c
              let a_tmp = a*a - b*b + ca;
              let b_tmp = 2*a*b + cb;
              a = a_tmp;
              b = b_tmp;
              count++;
            }
          
          // 2 Color
          let color = dist(a,b,0,0) < border ? 10.0 : 220.0;
          stroke(color);
          point(x,y);
        }
    }
}

function setup() {
  createCanvas(1200, 800);
  noLoop();
}

function draw() {
  background(220);
  
  // offset c
  let ca = -0.6778;
  let cb = 0.3245;
  drawJuliaSet(ca, cb);
}