HTML5 Canvas Experiment: A cool flame/fire effect using particles

<!-- Lets make a cool flame effect -->

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

/*Some styles*/

* {margin: 0; padding: 0;}

#canvas {display: block;}

window.onload = function(){

    var canvas = document.getElementById("canvas");

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

    //Make the canvas occupy the full page

    var W = window.innerWidth, H = window.innerHeight;

    canvas.width = W;

    canvas.height = H;

    var particles = [];

    var mouse = {};

    //Lets create some particles now

    var particle_count = 100;

    for(var i = 0; i < particle_count; i++)

    {

        particles.push(new particle());

    }

    //finally some mouse tracking

    canvas.addEventListener('mousemove', track_mouse, false);

    function track_mouse(e)

    {

        //since the canvas = full page the position of the mouse 

        //relative to the document will suffice

        mouse.x = e.pageX;

        mouse.y = e.pageY;

    }

    function particle()

    {

        //speed, life, location, life, colors

        //speed.x range = -2.5 to 2.5 

        //speed.y range = -15 to -5 to make it move upwards

        //lets change the Y speed to make it look like a flame

        this.speed = {x: -2.5+Math.random()*5, y: -15+Math.random()*10};

        //location = mouse coordinates

        //Now the flame follows the mouse coordinates

        if(mouse.x && mouse.y)

        {

            this.location = {x: mouse.x, y: mouse.y};

        }

        else

        {

            this.location = {x: W/2, y: H/2};

        }

        //radius range = 10-30

        this.radius = 10+Math.random()*20;

        //life range = 20-30

        this.life = 20+Math.random()*10;

        this.remaining_life = this.life;

        //colors

        this.r = Math.round(Math.random()*255);

        this.g = Math.round(Math.random()*255);

        this.b = Math.round(Math.random()*255);

    }

    function draw()

    {

        //Painting the canvas black

        //Time for lighting magic

        //particles are painted with "lighter"

        //In the next frame the background is painted normally without blending to the 

        //previous frame

        ctx.globalCompositeOperation = "source-over";

        ctx.fillStyle = "black";

        ctx.fillRect(0, 0, W, H);

        ctx.globalCompositeOperation = "lighter";

        for(var i = 0; i < particles.length; i++)

        {

            var p = particles[i];

            ctx.beginPath();

            //changing opacity according to the life.

            //opacity goes to 0 at the end of life of a particle

            p.opacity = Math.round(p.remaining_life/p.life*100)/100

            //a gradient instead of white fill

            var gradient = ctx.createRadialGradient(p.location.x, p.location.y, 0, p.location.x, p.location.y, p.radius);

            gradient.addColorStop(0, "rgba("+p.r+", "+p.g+", "+p.b+", "+p.opacity+")");

            gradient.addColorStop(0.5, "rgba("+p.r+", "+p.g+", "+p.b+", "+p.opacity+")");

            gradient.addColorStop(1, "rgba("+p.r+", "+p.g+", "+p.b+", 0)");

            ctx.fillStyle = gradient;

            ctx.arc(p.location.x, p.location.y, p.radius, Math.PI*2, false);

            ctx.fill();

            //lets move the particles

            p.remaining_life--;

            p.radius--;

            p.location.x += p.speed.x;

            p.location.y += p.speed.y;

            //regenerate particles

            if(p.remaining_life < 0 || p.radius < 0)

            {

                //a brand new particle replacing the dead one

                particles[i] = new particle();

            }

        }

    }

    setInterval(draw, 33);

}