<!doctype html>
<
html
lang
=
"en"
>
<
head
>
<
meta
charset
=
"UTF-8"
>
<
meta
name
=
"Generator"
content
=
""
>
<
meta
name
=
"Author"
content
=
""
>
<
meta
name
=
"Keywords"
content
=
""
>
<
meta
name
=
"Description"
content
=
""
>
<
title
>下雪</
title
>
<
style
>
*{padding:0;margin:0}
html{overflow:hidden}
</
style
>
</
head
>
<
body
>
<
canvas
id
=
"canvas"
style
=
"background:#111"
></
canvas
>
<
audio
src
=
"http://dx.sc.chinaz.com/Files/DownLoad/sound1/201210/2178.mp3"
autoplay loop/>
<
audio
src
=
"http://dx.sc.chinaz.com/Files/DownLoad/sound1/201205/1430.mp3"
autoplay loop/>
<
script
type
=
"text/javascript"
>
window.onload = function(){
//获取画布对象
var canvas = document.getElementById("canvas");
//获取画布的上下文
var context =canvas.getContext("2d");
//获取浏览器屏幕的宽度和高度
var w = window.innerWidth;
var h = window.innerHeight;
//设置canvas的宽度和高度
canvas.width = w;
canvas.height = h;
//1:如何产生雪花,一个圆 ,arc(x,y,r,start,end)
//初始化雪花数量
var num = 200;
//雪花数组
var snows = [];
for(var i=0;i<
num
;i++){
//x,y圆心掉的坐标位置,r代表圆的半径,d每个圆的每个圆之间的间距,c代表的颜色
var
r
=
randColor
();
snows.push({
x:Math.random()*w,
y:Math.random()*h,
r:Math.random()*10,
d:Math.random()*num
});
};
//绘画的函数
function draw(){
context.clearRect(0,0,w,h);
context.beginPath();
for(var
i
=
0
;i<num;i++){
var
snow
=
snows
[i];
context.fillStyle
=
"rgba(255,255,255,0.9)"
;
context.moveTo(snow.x,snow.y);
context.arc(snow.x,snow.y,snow.r,0,Math.PI*2);
}
context.fill();
//掉落
drop();
};
var
angle
=
0
;
function drop()
{
angle += 0.01;
for(var
i
=
0
; i < num; i++){
var
p
=
snows
[i];
//记住两个公式:Math.sin(弧度)返回是一个0 1 -1 的数字
//math.cos(1 0 -1 ) 自由体,
p.y += Math.cos(angle+p.d) + 1 + p.r*0.625;
p.x += Math.sin(angle) * 8 ;
//如果雪花到了边界,进行边界处理
if(p.x > w+5 || p.x < -5 || p.y > h){
if(i%4 > 0) {
snows[i] = {x: Math.random()*w, y: -10, r: p.r, d: p.d};
}else{
//控制方向
if(Math.sin(angle) > 0){
snows[i] = {x: -5, y: Math.random()*h, r: p.r, d: p.d};
}else{
snows[i] = {x: w+5, y: Math.random()*h, r: p.r, d: p.d};
}
}
}
}
};
//执行和调用函数
draw();
setInterval(draw,10);
//随机颜色
function randColor(){
var r = Math.floor(Math.random() * 256);
var g = Math.floor(Math.random() * 256);
var b = Math.floor(Math.random() * 256);
return "rgb("+r+","+g+","+b+")";
};
};
</
script
>
</
body
>
</
html
>