HTMLpractice/pt4.html at master · orcarex/HTMLpractice · GitHub

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<!DOCTYPE html>
<html>
   <head>
    <style>
        *{
            padding: 0;
            margin: 0;
        }
        body{
            background-color: azure;

        }
        canvas{
            background-color: pink;
            position: absolute;
            left: 0;
            right: 0;
            top: 0;
            bottom: 0;
            margin: auto;
        }
    </style>
</head>
<body>

    <canvas width="400" height="400"></canvas>

</body>
    <script type="text/javascript">
        window.onload=function(){

            var canvas = document.querySelector("canvas");
            //取得筆
            if(canvas.getContext){

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

                ctx.save();
                ctx.beginPath();
                ctx.fillStyle="black";
                ctx.fillRect(0,0,200,200);
                ctx.restore();

                ctx.save();
                ctx.beginPath();
                ctx.fillStyle="yellow";
                ctx.arc(100,100,50,0,360*Math.PI/180);
                ctx.fill();
                ctx.restore();
            }

        }
    </script>
</html>