canvas初体验

利用画布，绘制随机大小，颜色，位置 方框
<!DOCTYPE html>

<html lang="en">

<head>

    <meta charset="UTF-8">

    <title>H5-canvas</title>

    <style type="text/css">

        canvas{background: #f1aaa3; margin: 80px auto; display: block;}

    </style>

</head>

<body >

    <canvas id="canvas" width="900px" height="468px">

    </canvas>

</body>

<script type="text/javascript">

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

    var context = canvas.getContext("2d");

    var width = canvas.width;

    var height = canvas.height;

    // context.fillStyle = "#008ce1";  //填充色

 //     context.strokeStyle = "#515151";  //描边色

 //     context.globalAlpha = 0.5;   // 透明度

    // context.fillRect(10,20,100,100); //x,y,w,h 方形

    // context.strokeRect(10,150,88,88); //描边

    // context.clearRect(20,30,50,50); //橡皮擦

    //随机颜色函数

    function randomColor(){

        var r = Math.floor(Math.random()*256);

        var g = Math.floor(Math.random()*256);

        var b = Math.floor(Math.random()*256);

        var color = 'rgb('+r+','+g+','+b+')';

        console.log(color);

        return color;

    }

    //canvas内随机位置大小方框函数

    function randomSize(){

      var x = Math.random()*width;

      var y = Math.random()*height;

      var w = Math.random()*(width-x);

      var h = Math.random()*(height-y);

      var data = [x,y,w,h];

      console.log(data);

      return data;

    }

    //canvas内随机位置出现随机大小颜色方框

    function randomRect(){

        context.strokeStyle = randomColor();

        var data = randomSize();

        context.strokeRect(data[0],data[1],data[2],data[3]);

        //递归每隔0.5秒执行一次当前函数

        setTimeout(randomRect,500);

    }

    randomRect();

</script>

</html>
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