CANVAS 水波动态背景

参考：https://github.com/cyclegtx/wave_background

做的水波背景，以后可能会用到哈！

效果如下：

代码如下：

<!DOCTYPE html>
<html>
<head>
    <title>水波背景</title>
    <meta charset="utf-8" />
    <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>
</html>

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原文地址：https://www.cnblogs.com/zjfree/p/5379308.html