點評：本示例通過Javascript使用HTML5的canvas元素在屏幕上顯示一個跳動的火焰，火焰會跟隨光標跳動
本效果的完整代碼如下,把代碼保存到HTML文件中打開也能查看效果,火焰會跟隨光標:
<!DOCTYPE HTML>
<head>
<meta charset=utf-8" />
<title>HTML5 Canvas火焰效果</title>
<style type="text/css">
body{margin: 0; padding: 0;}
#canvas-keleyi-com {display: block;}
</style>
</head>
<body>
<canvas></canvas>
<script type="text/javascript">
window.onload = function(){
var keleyi_canvas = document.getElementById("canvas-kel"+"eyi-com");
var ctx = keleyi_canvas.getContext("2d");
var W = window.innerWidth, H = window.innerHeight;
keleyi_canvas.width = W;
keleyi_canvas.height = H;</p><p>var particles = [];
var mouse = {};</p><p>//Lets create some particles now
var particle_count = 100;
for(var i = 0; i < particle_count; i++)
{
particles.push(new particle());
}
keleyi_canvas.addEventListener('mousemove', track_mouse, false);</p><p>function track_mouse(e)
{
mouse.x = e.pageX;
mouse.y = e.pageY;
}</p><p>function particle()
{
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);
}</p><p>function draw()
{
ctx.globalCompositeOperation = "source-over";
ctx.fillStyle = "black";
ctx.fillRect(0, 0, W, H);
ctx.globalCompositeOperation = "lighter";</p><p>for(var i = 0; i < particles.length; i++)
{
var p = particles[i];
ctx.beginPath();
p.opacity = Math.round(p.remaining_life/p.life*100)/100
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();</p><p>
p.remaining_life--;
p.radius--;
p.location.x += p.speed.x;
p.location.y += p.speed.y;</p><p>if(p.remaining_life < 0 || p.radius < 0)
{
particles[i] = new particle();
}
}
}</p><p>setInterval(draw, 86);
}
</script>
</body>
</html>