本文实例讲述了基于html5 canvas实现漫天飞雪效果的方法，运行该实例可以看到很棒的下雪效果。如下图所示：

主要代码如下：

复制代码代码如下:

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漫天飞雪

* {margin: 0; padding: 0;}

body {

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

background: #6b92b9;

}

canvas {

display: block;

}

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);

}

代码分析如下：

这行代码改变雪花半径大小：

复制代码代码如下:

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

这行代码改变雪花下落速度：

复制代码代码如下:

setInterval(draw, 15);

这行值改变雪花密度：

复制代码代码如下:

var mp = 3000; //max particles

相信本文所述对大家的html5 WEB程序设计有一定的借鉴价值。