canvasClip.html

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>canvas的剪辑区域</title>
</head>
<body>
        <canvas id="myCanvas" style="background:#333" width="1000" height="1000">
                <p>你的浏览器不支持Canvas</p>
            </canvas>
        
        <script>
            window.onload = function(){
                // 按钮
            
          
                var canvas = document.getElementById('myCanvas'),
                ctx = canvas.getContext('2d');
                ctx.beginPath();
                ctx.arc(300,300,100,0,2*Math.PI);
                ctx.fillStyle="#fff";
                ctx.fill();
                ctx.clip();
                ctx.font="bold 24px Arial";
                ctx.fillStyle="#058";
                ctx.textAlign="center";
                ctx.fillText("this is a test clip ,attention",300,300);
                
            }
        </script> 
</body>
</html>