飘雪代码2枚

代码一

<title>Snow</title>
<style type="text/css">

canvas {
display: block;
}
</style>

<p>
<canvas id="canvas" style="position:fixed; top:0px;left:0px;z-index:80;pointer-events:none;" width="1261" height="764"></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 = 500; //max particles:3000
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>
</p>

　　

代码二

<style>#Snow{position:fixed;top:0;left:0;width:100%;height:100%;z-index:99999;background:RGB(225,225,225,0.1);pointer-events:none}</style>

<p>
<canvas id="Snow" width="1366" height="274"></canvas>
</p>

<p>
<script>(function() {
        var requestAnimationFrame = window.requestAnimationFrame || window.mozRequestAnimationFrame || window.webkitRequestAnimationFrame || window.msRequestAnimationFrame ||
        function(callback) {
            window.setTimeout(callback, 1000 / 60);
        };
        window.requestAnimationFrame = requestAnimationFrame;
    })();
    (function() {
        var flakes = [],
            canvas = document.getElementById("Snow"),
            ctx = canvas.getContext("2d"),
            flakeCount = 200,
            mX = -100,
            mY = -100
            canvas.width = window.innerWidth;
        canvas.height = window.innerHeight;
        function snow() {
            ctx.clearRect(0, 0, canvas.width, canvas.height);
            for (var i = 0; i < flakeCount; i++) {
                var flake = flakes[i],
                    x = mX,
                    y = mY,
                    minDist = 150,
                    x2 = flake.x,
                    y2 = flake.y;
                var dist = Math.sqrt((x2 - x) * (x2 - x) + (y2 - y) * (y2 - y)),
                    dx = x2 - x,
                    dy = y2 - y;
                if (dist < minDist) {
                    var force = minDist / (dist * dist),
                        xcomp = (x - x2) / dist,
                        ycomp = (y - y2) / dist,
                        deltaV = force / 2;
                    flake.velX -= deltaV * xcomp;
                    flake.velY -= deltaV * ycomp;
                } else {
                    flake.velX *= 0.98;
                    if (flake.velY <= flake.speed) {
                        flake.velY = flake.speed
                    }
                    flake.velX += Math.cos(flake.step += .05) * flake.stepSize;
                }
                ctx.fillStyle = "rgba(255,255,255," + flake.opacity + ")";
                flake.y += flake.velY;
                flake.x += flake.velX;
                if (flake.y >= canvas.height || flake.y <= 0) {
                    reset(flake);
                }
                if (flake.x >= canvas.width || flake.x <= 0) {
                    reset(flake);
                }
                ctx.beginPath();
                ctx.arc(flake.x, flake.y, flake.size, 0, Math.PI * 2);
                ctx.fill();
            }
            requestAnimationFrame(snow);
        };
        function reset(flake) {
            flake.x = Math.floor(Math.random() * canvas.width);
            flake.y = 0;
            flake.size = (Math.random() * 3) + 2;
            flake.speed = (Math.random() * 1) + 0.5;
            flake.velY = flake.speed;
            flake.velX = 0;
            flake.opacity = (Math.random() * 0.5) + 0.3;
        }
        function init() {
            for (var i = 0; i < flakeCount; i++) {
                var x = Math.floor(Math.random() * canvas.width),
                    y = Math.floor(Math.random() * canvas.height),
                    size = (Math.random() * 3) + 2,
                    speed = (Math.random() * 1) + 0.5,
                    opacity = (Math.random() * 0.5) + 0.3;
                flakes.push({
                    speed: speed,
                    velY: speed,
                    velX: 0,
                    x: x,
                    y: y,
                    size: size,
                    stepSize: (Math.random()) / 30 * 1,
                    step: 0,
                    angle: 180,
                    opacity: opacity
                });
            }
            snow();
        };
        document.addEventListener("mousemove", function(e) {
            mX = e.clientX,
            mY = e.clientY
        });
        window.addEventListener("resize", function() {
            canvas.width = window.innerWidth;
            canvas.height = window.innerHeight;
        });
        init();
    })();</script>
</p>