stars.metajs

var julia = function(x, y) {
  var newX, newY, c=.52;
  //x /= w*.6; // star field based on browser width
  //y /= w*.6; // star field based on browser width
  x /= bgZ; // star field fixed width
  y /= bgZ; // star field fixed width
  for (var i = 1; i <= 255; i++) {
    var x2 = x*x, y2 = y*y;
    if(x2 + y2 > 4) break;
    newX = x2 - y2 + -c;
    newY = 2*x*y + c;
    x = newX;
    y = newY;
  }
  return i;
};

var pseudoRandPx = function(x, y, probability) {
  return (x*y+start) % ((((x+1e4)/(y+1e3))%77)+13) < (probability||1);
};

var coord2index = function(x, y) {
  //var index = w*bgZFactor*(y+h*(bgZFactor/2)) + x+w*(bgZFactor/2); // star field based on browser width
  var index = bgW*(y+bgH/2) + x+bgW/2; // star field fixed width
  if (index < 0) index = 0;
  return index;
};

var setPxLight = function(imgData, x,y, alpha) {
  var i = coord2index(x,y);
  imgData[i*4+0] = 255*alpha; // R
  imgData[i*4+1] = 400*alpha; // G
  imgData[i*4+2] = 600*alpha; // B
  imgData[i*4+3] = alpha*255; // A
};

var plotStar = function(imgData, x,y, alpha) {
  setPxLight(imgData, x,y, alpha);
  setPxLight(imgData, x,y+1, alpha*.6);
  setPxLight(imgData, x+1,y, alpha*.6);
  setPxLight(imgData, x+1,y+1, alpha*.6);
  if (alpha>.5) {
    setPxLight(imgData, x-1, y+1, alpha/2);
    setPxLight(imgData, x+2, y,   alpha/2);
    setPxLight(imgData, x,   y-1, alpha/2);
    setPxLight(imgData, x+1, y+2, alpha/2);
  }
};

window.onload = function() {
  // Create the image storage to the stars
  //var imgDataObj = ctxBg.createImageData(w*bgZFactor,h*bgZFactor); // star field based on browser width
  var imgDataObj = ctxBg.createImageData(bgW,bgH); // star field fixed width
  var imgData = imgDataObj.data;
  //for (var x=-w*(bgZFactor/2); x<w*(bgZFactor/2); x++) { // star field based on browser width
    //for (var y=-h*(bgZFactor/2); y<h*(bgZFactor/2); y++) {
  for (var x=-bgW; x<bgW; x++) { // star field fixed width
    for (var y=-bgH; y<bgH; y++) {
      var alpha = julia(x,y)/255;
      if (alpha>.6 && pseudoRandPx(x,y,1.5)) plotStar(imgData, x,y, alpha*.4);
      if (alpha>.4 && pseudoRandPx(x,y,0.7)) plotStar(imgData, x,y, alpha*.5);
      if (pseudoRandPx(x,y,0.2)) plotStar(imgData, x,y, alpha);
    }
  }
  // Set bg attributes
  //bg.style.width = (bg.width = Math.round(w*bgZFactor))+'px'; // star field based on browser width
  //bg.style.height = (bg.height = Math.round(h*bgZFactor))+'px';
  bg.style.width = (bg.width = bgW)+'px'; // star field fixed width
  bg.style.height = (bg.height = bgH)+'px';
  //bg.style.left = -(bgW-w)/2 +'px';
  //bg.style.top = -(bgH-h)/2 +'px';
  ctxBg.clearRect(0,0,bgW,bgH);
  ctxBg.putImageData(imgDataObj, 0, 0);
  window.introNext();
  setTimeout(function() {
    pressDialogBt = window.introNext;
    introNextBt.style.display = 'inline-block';
  }, secs(2));
};