下雪執行個體
知識點：
- canvas畫布
- 數組
- 繪畫函數
效果：
源碼：
<!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(){
//擷取畫布對象
var canvas = document.getElementById("canvas");
//擷取畫布的上下文
var context =canvas.getContext("2d");
//擷取浏覽器螢幕的寬度和高度
var w = window.innerWidth;
var h = window.innerHeight;
//設定canvas的寬度和高度
canvas.width = w;
canvas.height = h;
//1：如何産生雪花,一個圓 ,arc(x,y,r,start,end)
//初始化雪花數量
var num = 200;
//雪花數組
var snows = [];
for(var i=0;i<num;i++){
//x,y圓心掉的坐标位置，r代表圓的半徑，d每個圓的每個圓之間的間距，c代表的顔色
var r = randColor();
snows.push({
x:Math.random()*w,
y:Math.random()*h,
r:Math.random()*10,
d:Math.random()*num
});
};
//繪畫的函數
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];
//記住兩個公式：Math.sin(弧度)傳回是一個0 1 -1 的數字
//math.cos(1 0 -1 ) 自由體，
p.y += Math.cos(angle+p.d) + 1 + p.r*0.625;
p.x += Math.sin(angle) * 8 ;
//如果雪花到了邊界，進行邊界處理
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};
}
}
}
}
};
//執行和調用函數
draw();
setInterval(draw,10);
//随機顔色
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> ![10款優秀的 HTML5 動畫工具[圖]](data:image/gif;base64,R0lGODlhAQABAIAAAP///wAAACwAAAAAAQABAAACAkQBADs=)