一起来看流星雨

var context;

var arr = new Array();

var starCount = 800;

var rains = new Array();

var rainCount =20;

//初始化画布及context

function init(){

//获取canvas

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

windowWidth = window.innerWidth; //当前的窗口的高度

stars.width=windowWidth;

stars.height=window.innerHeight;

//获取context

context = stars.getContext("2d");

}

//创建一个星星对象

var Star = function (){

this.x = windowWidth * Math.random();//横坐标

this.y = 5000 * Math.random();//纵坐标

this.text=".";//文本

this.color = "white";//颜色

//产生随机颜色

this.getColor=function(){

var _r = Math.random();

if(_r<0.5){

this.color = "#333";

}else{

this.color = "white";

}

}

//初始化

this.init=function(){

this.getColor();

}

//绘制

this.draw=function(){

context.fillStyle=this.color;

context.fillText(this.text,this.x,this.y);

}

}

//画月亮

function drawMoon(){

var moon = new Image();

moon.src = "./images/moon.jpg"

context.drawImage(moon,-5,-10);

}

//页面加载的时候

window.onload = function() {

init();

//画星星

for (var i=0;i

var star = new Star();

star.init();

star.draw();

arr.push(star);

}

//画流星

for (var i=0;i

var rain = new MeteorRain();

rain.init();

rain.draw();

rains.push(rain);

}

drawMoon();//绘制月亮

playStars();//绘制闪动的星星

playRains();//绘制流星

}

//星星闪起来

function playStars(){

for (var n = 0; n < starCount; n++){

arr[n].getColor();

arr[n].draw();

}

setTimeout("playStars()",100);

}

/*流星雨开始*/

var MeteorRain = function(){

this.x = -1;

this.y = -1;

this.length = -1;//长度

this.angle = 30; //倾斜角度

this.width = -1;//宽度

this.height = -1;//高度

this.speed = 1;//速度

this.offset_x = -1;//横轴移动偏移量

this.offset_y = -1;//纵轴移动偏移量

this.alpha = 1; //透明度

this.color1 = "";//流星的色彩

this.color2 = ""; //流星的色彩

/****************初始化函数********************/

this.init = function () //初始化

{

this.getPos();

this.alpha = 1;//透明度

this.getRandomColor();

//最小长度，最大长度

var x = Math.random() * 80 + 150;

this.length = Math.ceil(x);

// x = Math.random()*10+30;

this.angle = 30; //流星倾斜角

x = Math.random()+0.5;

this.speed = Math.ceil(x); //流星的速度

var cos = Math.cos(this.angle*3.14/180);

var sin = Math.sin(this.angle*3.14/180) ;

this.width = this.length*cos ; //流星所占宽度

this.height = this.length*sin ;//流星所占高度

this.offset_x = this.speed*cos ;

this.offset_y = this.speed*sin;

}

/**************获取随机颜色函数*****************/

this.getRandomColor = function (){

var a = Math.ceil(255-240* Math.random());

//中段颜色

this.color1 = "rgba("+a+","+a+","+a+",1)";

//结束颜色

this.color2 = "black";

}

/***************重新计算流星坐标的函数******************/

this.countPos = function ()//

{

//往左下移动,x减少，y增加

this.x = this.x - this.offset_x;

this.y = this.y + this.offset_y;

}

/*****************获取随机坐标的函数*****************/

this.getPos = function () //

{

//横坐标200--1200

this.x = Math.random() * window.innerWidth; //窗口高度

//纵坐标小于600

this.y = Math.random() * window.innerHeight; //窗口宽度

}

/****绘制流星***************************/

this.draw = function () //绘制一个流星的函数

{

context.save();

context.beginPath();

context.lineWidth = 1; //宽度

context.globalAlpha = this.alpha; //设置透明度

//创建横向渐变颜色,起点坐标至终点坐标

var line = context.createLinearGradient(this.x, this.y,

this.x + this.width,

this.y - this.height);

//分段设置颜色

line.addColorStop(0, "white");

line.addColorStop(0.3, this.color1);

line.addColorStop(0.6, this.color2);

context.strokeStyle = line;

//起点

context.moveTo(this.x, this.y);

//终点

context.lineTo(this.x + this.width, this.y - this.height);

context.closePath();

context.stroke();

context.restore();

}

this.move = function(){

//清空流星像素

var x = this.x+this.width-this.offset_x;

var y = this.y-this.height;

context.clearRect(x-3,y-3,this.offset_x+5,this.offset_y+5);

// context.strokeStyle="red";

// context.strokeRect(x,y-1,this.offset_x+1,this.offset_y+1);

//重新计算位置，往左下移动

this.countPos();

//透明度增加

this.alpha -= 0.002;

//重绘

this.draw();

}

}

//绘制流星

function playRains(){

for (var n = 0; n < rainCount; n++){

var rain = rains[n];

rain.move();//移动

if(rain.y>window.innerHeight){//超出界限后重来

context.clearRect(rain.x,rain.y-rain.height,rain.width,rain.height);

rains[n] = new MeteorRain();

rains[n].init();

}

}

setTimeout("playRains()",2);

}

/*流星雨结束*/

body{

background-color: black;

}

body,html{width:100%;height:100%;overflow:hidden;}