let pi = CalculatePi(decimals).replace(/([^0-9])/g,"");

​

function setup() {

  createCanvas(400, 200);

  colorMode(HSB,9,1,1);

  noStroke();

}

​

function draw() {

  background(0,0,0.5);

  n = floor(decimals*mouseX/width);

  for (i=0;i<=n;i++){

    digit = int(pi.substring(i,i+1));

    fill(digit,0.5,1);

    rect (i*width/n,height,width/n,-20*digit);

    // fill(0,0,1);

    text (digit, i*width/n,height-20*digit-5);

  }

}

​

// PI decimals calculation borrowed from: http://cosinekitty.com/pi.html

​

function CalculatePi(digits) {

  var numDigits = parseInt(digits);

  var numQuads = 3 + Math.floor((numDigits + 3) / 4); // extra quads for accuracy

  BigMath_SetPrecision(numQuads);

  var formula = [48, 18, 32, 57, -20, 239]; // pi = 48*arctan(1/18) + 32*arctan(1/57) - 20*arctan(1/239)

  var sum = new BigReal("0");

  for (var i = 0; i < formula.length; i += 2) {

    var factor = formula[i];

    var denom = formula[i + 1];

    var term = BigReal_ArctanRecip(denom);

    term = term.multiplyByInteger(factor);

    sum = sum.add(term);

  }

  return sum.toSimpleString();

}