火焰鼠标跟随 canvas

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<!DOCTYPE HTML><html><head><meta charset="utf-8" /><title>HTML5 Canvas火焰效果</title><style>.body{  }#myCanvas{  position: absolute;  left: 0px;  top: 0px;}</style><script>window.onload = function(){var canvas = document.getElementById("myCanvas");var ctx = canvas.getContext("2d");//Make the canvas occupy the full pagevar W = window.innerWidth, H = window.innerHeight;canvas.width = W;canvas.height = H;var particles = [];var mouse = {};//Lets create some particles nowvar particle_count = 50;for(var i = 0; i < particle_count; i++){particles.push(new particle());}//finally some mouse trackingcanvas.addEventListener('mousemove', track_mouse, false);function track_mouse(e){//since the canvas = full page the position of the mouse //relative to the document will sufficemouse.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 flamethis.speed = {x: -2.5+Math.random()*5, y: -15+Math.random()*10};//location = mouse coordinates//Now the flame follows the mouse coordinatesif(mouse.x && mouse.y){this.location = {x: mouse.x, y: mouse.y};}else{this.location = {x: W/2, y: H/2};}//radius range = 10-30this.radius = 10+Math.random()*20;//life range = 20-30this.life = 20+Math.random()*10;this.remaining_life = this.life;//colorsthis.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 framectx.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 particlep.opacity = Math.round(p.remaining_life/p.life*100)/100//a gradient instead of white fillvar 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 particlesp.remaining_life--;p.radius--;p.location.x += p.speed.x;p.location.y += p.speed.y;//regenerate particlesif(p.remaining_life < 0 || p.radius < 0){//a brand new particle replacing the dead oneparticles[i] = new particle();}}}setInterval(draw, 30);}</script></head><body>  <img src="css/logo_topbar.png" id="scream"><canvas id="myCanvas">Your browser does not support the HTML5 canvas tag.</canvas></body></html>
效果图：
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