下雪实例
知识点：
- canvas画布
- 数组
- 绘画函数
效果：
源码：
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<!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>
