Gen. image seq. from dotty Redis data

1frameanimate.js

var redis  = require('redis'),
    fs     = require('fs'),
    Canvas = require('canvas');

var db = redis.createClient(),
    canvas = new Canvas(500, 300),
    ctx = canvas.getContext('2d');

function pad(number, length) {
    var str = '' + number;
    while (str.length < length) {
        str = '0' + str;
    }
    return str;
}

function draw_dot(dot, i){

  //Pad frame # with 6 zeros
  frame = pad(i, 6);

  //Draw da dots
  var obj = JSON.parse(dot);
  var x = obj.x,
      y = obj.y,
      color = obj.color;
  ctx.beginPath();
  ctx.arc(x, y, 8, 0, Math.PI*2, true);
  ctx.closePath();
  ctx.fillStyle = '#'+color;
  ctx.fill();

  //Create PNG stream for current frame context
  var out = fs.createWriteStream(__dirname + '/frames1/' + frame + '.png'),
      stream = canvas.createPNGStream();
  
  //Pipe the PNG stream to the write file stream
  stream.pipe(out);

  //listen for close event from writeable stream
  out.on('close', function(){

      //hardcoded callback...
      main(i);
      console.log(i);
  });
}

function main(i){
  if(i<length){
    i++;

    //Look at redis for next range of dots
    db.lindex('dotty:dots',i, function(err, dot){
      if(err) throw err;
      draw_dot(dot, i);
    });
  }
}

db.llen('dotty:dots', function(err, len){
  length = len;
  main(-1);
});