canvas 水波纹

<!DOCTYPE html>

<html>

<head>

 <title>水波背景</title>

 <meta charset="gb2312" />

 <style>

 html, body {width:100%; height:100%; padding:0; margin:0;}

 </style>

</head>

<body>

 <canvas id="canvas" style="position:absolute;top:0px;left:0px;z-index:1;"></canvas>

 <script type="text/javascript">

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

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

  canvas.width = canvas.parentNode.offsetWidth;

  canvas.height = canvas.parentNode.offsetHeight;

  //如果浏览器支持requestAnimFrame则使用requestAnimFrame否则使用setTimeout

  window.requestAnimFrame = (function(){

  return window.requestAnimationFrame  ||

    window.webkitRequestAnimationFrame ||

    window.mozRequestAnimationFrame ||

    function( callback ){

     window.setTimeout(callback, 1000 / 60);

    };

  })();

  // 波浪大小

  var boHeight = canvas.height / 10;

  var posHeight = canvas.height / 1.2;

  //初始角度为0

  var step = 0;

  //定义三条不同波浪的颜色

  var lines = ["rgba(0,222,255, 0.2)",

      "rgba(157,192,249, 0.2)",

      "rgba(0,168,255, 0.2)"];

  function loop(){

   ctx.clearRect(0,0,canvas.width,canvas.height);

   step++;

   //画3个不同颜色的矩形

   for(var j = lines.length - 1; j >= 0; j--) {

    ctx.fillStyle = lines[j];

    //每个矩形的角度都不同，每个之间相差45度

    var angle = (step+j*50)*Math.PI/180;

    var deltaHeight = Math.sin(angle) * boHeight;

    var deltaHeightRight = Math.cos(angle) * boHeight;

    ctx.beginPath();

    ctx.moveTo(0, posHeight+deltaHeight);

    ctx.bezierCurveTo(canvas.width/2, posHeight+deltaHeight-boHeight, canvas.width / 2, posHeight+deltaHeightRight-boHeight, canvas.width, posHeight+deltaHeightRight);

    ctx.lineTo(canvas.width, canvas.height);

    ctx.lineTo(0, canvas.height);

    ctx.lineTo(0, posHeight+deltaHeight);

    ctx.closePath();

    ctx.fill();

   }

   requestAnimFrame(loop);

  }

  loop();

 </script>

</body>
巴特西

canvas 水波纹

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