<script language="JavaScript">
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);
}
</script>
