基于html5 canvas實(shí)現(xiàn)漫天飛雪效果實(shí)例
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本文實(shí)例講述了基于html5 canvas實(shí)現(xiàn)漫天飛雪效果的方法,運(yùn)行該實(shí)例可以看到很棒的下雪效果。如下圖所示:

名單

主要代碼如下:

>">

<html xmlns="<a href=">">

<head>

<meta http-equiv="Content-Type" content="text/html; charset=gb2312" />

<title>漫天飛雪</title>

<style type="text/css">

* {margin: 0; padding: 0;}</p> <p>body {

/*You can use any kind of background here.*/

background: #6b92b9;

}

canvas {

display: block;

}

</style>

</head></p> <p><body></p> <p><div style=" background:#6b92b9; width:100%; height:2000px;" ></div>

<canvas id="canvas" style="position:fixed; top:0px;left:0px;z-index:80;pointer-events:none;"></canvas></p> <p><script>

window.onload = function(){

//canvas init

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

var ctx = canvas.getContext("2d");

//canvas dimensions

var W = window.innerWidth;

var H = window.innerHeight;

canvas.width = W;

canvas.height = H;

//snowflake particles

var mp = 3000; //max particles

var particles = [];

for(var i = 0; i < mp; i++)

{

particles.push({

x: Math.random()*W, //x-coordinate

y: Math.random()*H, //y-coordinate

r: Math.random()*3+1, //radius

d: Math.random()*mp //density

})

}

//Lets draw the flakes

function draw()

{

ctx.clearRect(0, 0, W, H);

ctx.fillStyle = "rgba(255, 255, 255, 0.8)";

/* ctx.fillStyle = "#FF0000";*/

ctx.beginPath();

for(var i = 0; i < mp; i++)

{

var p = particles[i];

ctx.moveTo(p.x, p.y);

ctx.arc(p.x, p.y, p.r, 0, Math.PI*2, true);

}

ctx.fill();

update();

}

//Function to move the snowflakes

//angle will be an ongoing incremental flag. Sin and Cos functions will be applied to it to create vertical and horizontal movements of the flakes

var angle = 0;

function update()

{

angle += 0.01;

for(var i = 0; i < mp; i++)

{

var p = particles[i];

//Updating X and Y coordinates

//We will add 1 to the cos function to prevent negative values which will lead flakes to move upwards

//Every particle has its own density which can be used to make the downward movement different for each flake

//Lets make it more random by adding in the radius

p.y += Math.cos(angle+p.d) + 1 + p.r/2;

p.x += Math.sin(angle) * 2;

//Sending flakes back from the top when it exits

//Lets make it a bit more organic and let flakes enter from the left and right also.

if(p.x > W || p.x < 0 || p.y > H)

{

if(i%3 > 0) //66.67% of the flakes

{

particles[i] = {x: Math.random()*W, y: -10, r: p.r, d: p.d};

}

else

{

//If the flake is exitting from the right

if(Math.sin(angle) > 0)

{

//Enter fromth

particles[i] = {x: -5, y: Math.random()*H, r: p.r, d: p.d};

}

else

{

//Enter from the right

particles[i] = {x: W+5, y: Math.random()*H, r: p.r, d: p.d};

}

}

}

}

}

//animation loop

setInterval(draw, 15);

}

</script>

</body>

</html>

代碼分析如下:

這行代碼改變雪花半徑大?。?/P>

復(fù)制代碼代碼如下:r: Math.random()*3+1, //radius

這行代碼改變雪花下落速度:

復(fù)制代碼代碼如下:setInterval(draw, 15);

這行值改變雪花密度:

復(fù)制代碼代碼如下:var mp = 3000; //max particles

相信本文所述對(duì)大家的html5 WEB程序設(shè)計(jì)有一定的借鑒價(jià)值。

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