cloud particles linear motion

working

HTML

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

JavaScript

//Lets create a simple particle system in HTML5 canvas and JS

//Initializing the canvas
var canvas = document.getElementById("canvas");
var ctx = canvas.getContext("2d");

var img = new Image();
img.src = 'http://aa8f47fcc01b7584f779-b57f388ffba74a9d5600392ce75da4b1.r13.cf2.rackcdn.com/cloud_2.png';
var skyImg = new Image();
skyImg.src = 'http://p1.pichost.me/640/41/1644656.jpg';

//Canvas dimensions
var W = window.innerWidth;
var H = window.innerHeight;

canvas.width = W;
canvas.height = H;



//Lets create an array of particles
var particles = [];
for (var i = 0; i < 100; i++) {
    //This will add 50 particles to the array with random positions
    particles.push(new create_particle());
}

//Lets create a function which will help us to create multiple particles
function create_particle() {
    //Random position on the canvas
    this.x = Math.random() * W;
    this.y = Math.random() * H;

    //Lets add random velocity to each particle
    this.vx = Math.random() * 20 - 1;
    this.vy = Math.random() * 20 - 1;

    //Random colors
    var r = Math.random() * 255 >> 0;
    var g = Math.random() * 255 >> 0;
    var b = Math.random() * 255 >> 0;
    this.color = "rgba(" + r + ", " + g + ", " + b + ", 0.5)";

    //Random size
    this.radius = Math.random() * 20 + 20;
}

var x = 100;
var y = 100;

//Lets animate the particle
function draw() {
    //Moving this BG paint code insde draw() will help remove the trail
    //of the particle
    //Lets paint the canvas black
    //But the BG paint shouldn't blend with the previous frame
    ctx.globalCompositeOperation = "source-over";
    //Lets reduce the opacity of the BG paint to give the final touch

    ctx.fillStyle = "rgba(0, 0, 0, 1)";   
    ctx.fillRect(0, 0, W, H);
    ctx.drawImage(skyImg, 0, 0, W, H);


    //Lets blend the particle with the BG
    //ctx.globalCompositeOperation = "lighter";



    //Lets draw particles from the array now
    for (var t = 0; t < particles.length; t++) {
        var p =...