js-graphics/starfield.htm at master · filetray/js-graphics · GitHub

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<!DOCTYPE html>
<html>
<head>
  <meta charset="utf-8" />
  <title>Starfield</title>
  <style>
  #canvas {
    position: absolute;
    top: 0;
    bottom: 0;
    left: 0;
    right: 0;
    width: 100%;
    height: 100%;
    display: block;
  }
  canvas {
    image-rendering: optimizeSpeed;
    image-rendering: -moz-crisp-edges;
    image-rendering: -webkit-optimize-contrast;
    image-rendering: -o-crisp-edges;
    image-rendering: crisp-edges;
    -ms-interpolation-mode: nearest-neighbor;
  }
  </style>
</head>
<body>

<canvas id="canvas"></canvas>

<script>
window.requestAnimFrame = (function(callback) {
  return window.requestAnimationFrame || window.webkitRequestAnimationFrame || window.mozRequestAnimationFrame || window.oRequestAnimationFrame || window.msRequestAnimationFrame || function(callback) {window.setTimeout(callback, 1000 / 60);};
})();
</script>

  <script>

  var stars_num = 200;
  var starColors = ["#ffc", "#cff", "#fff"];

  var q = window.innerHeight / window.innerWidth;

  var w = 320, h = Math.floor(q * w), d = 10;

  var canvas = document.getElementById("canvas");
  canvas.height = h;
  canvas.width = w;

  var ctx = canvas.getContext("2d");

  var Star = function()
  {
    this.x = 0;
    this.y = 0;
    this.z = 0;
    this.type = 1;
    this.speed = 1;
  };

  var cx = w / 2, cy = h / 2;
  var stars = new Array(stars_num);

  function randomInRange(m, M)
  {
    return Math.floor(Math.random() * (M - m) + m);
  }

  function createStar(i)
  {
    stars[i].x = randomInRange(-cx, cx);
    stars[i].y = randomInRange(-cy, cy);
    stars[i].z = randomInRange(1, 2 * d);
    stars[i].color = randomInRange(0, starColors.length);
  }

  function createStarfield()
  {
    for (var i = 0; i < stars.length; i++)
    {
      stars[i] = new Star();
      createStar(i);
    }
  }

  function drawStar(x, y, color)
  {
    ctx.fillStyle = color;
    ctx.fillRect(x, y, 1, 1);
  }

  function clearScreen()
  {
    ctx.fillStyle = "#000";
    ctx.fillRect(0, 0, w, h);
  }

  function moveStarfield()
  {
    clearScreen();
    for (var i = 0; i < stars.length; i++)
    {
      var star = stars[i];
      star.z -= 0.1 * (star.color + 1);
      if (star.z < 0)
      {
        createStar(i);
      }
      var color = starColors[star.color];
      var k = d / star.z;
      var px = Math.round(k * star.x + cx);
      var py = Math.round(k * star.y + cy);
      if (0 <= px && px <= w && 0 <= py && py <= h)
      {
        drawStar(px, py, color);
      }
    }
  }

  function startStarField()
  {
    moveStarfield();
    requestAnimFrame(startStarField);
  }

  function starField()
  {
    clearScreen();
    createStarfield();
    startStarField();
  }

  window.addEventListener("load", starField);

  </script>

</body>
</html>