本文實例講述了基于html5 canvas實現漫天飛雪效果的方法，運行該實例可以看到很棒的下雪效果。如下圖所示： 主要代碼如下： 復制代碼代碼如下: !DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" " a href="http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd" http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd /a " html xmlns=" a href="http://www.w3.org/1999/xhtml" http://www.w3.org/1999/xhtml /a " 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 /div canvas id="canvas" /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 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 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 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}; } } } } }
