Particle effect example

by SHELDON PASCIAK

HTML

<!-- Lets make a cool flame effect -->
<!-- From http://thecodeplayer.com/walkthrough/html5-canvas-experiment-a-cool-flame-fire-effect-using-particles -->
<canvas id="canvas"></canvas>

JavaScript

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 = 10;
	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...