canvas剪裁clip()涵数的实际应用

2021-02-23 10:02 jianzhan

在canvas中,可使用clip()涵数剪裁地区,设置剪裁地区后,仅有在地区内的图象才可以显示信息,其余一部分会被屏蔽掉

未应用剪裁绘图1个圆

<!DOCTYPE html>  
<html lang="en">  
<head>  
    <meta charset="UTF⑻">  
    <title></title>  
    <style>  
        *{margin:0; padding:0;}  
        html, body{width:100%; height:100%; overflow:hidden; background-color:#AFAFAF;}  
    </style>  
</head>  
<body>  
    <canvas id="canvas"></canvas>  
    <script>  
        var canvas = document.getElementById('canvas'),  
            context = canvas.getContext('2d');  
        canvas.width = document.body.clientWidth;  
        canvas.height = document.body.clientHeight;  
        context.lineWidth = 3;  
        context.strokeStyle = 'red';  
        context.beginPath();  
        context.arc(200, 200, 100, (Math.PI / 180) * 0, (Math.PI / 180) * 360, false);  
        context.stroke();  
        context.closePath();  
    </script>  
</body>  
</html>  

实际效果

应用clip()剪裁地区

<!DOCTYPE html>  
<html lang="en">  
<head>  
    <meta charset="UTF⑻">  
    <title></title>  
    <style>  
        *{margin:0; padding:0;}  
        html, body{width:100%; height:100%; overflow:hidden; background-color:#AFAFAF;}  
    </style>  
</head>  
<body>  
    <canvas id="canvas"></canvas>  
    <script>  
        var canvas = document.getElementById('canvas'),  
            context = canvas.getContext('2d');  
        canvas.width = document.body.clientWidth;  
        canvas.height = document.body.clientHeight;  
        context.lineWidth = 3;  
        context.strokeStyle = 'red';  
        context.rect(0, 0, 200, 200);  
        context.clip();  
        context.beginPath();  
        context.arc(200, 200, 100, (Math.PI / 180) * 0, (Math.PI / 180) * 360, false);  
        context.stroke();  
        context.closePath();  
    </script>  
</body>  
</html>  

实际效果

还可以应用arc绘图圆形的裁剪地区

<!DOCTYPE html>  
<html lang="en">  
<head>  
    <meta charset="UTF⑻">  
    <title></title>  
    <style>  
        *{margin:0; padding:0;}  
        html, body{width:100%; height:100%; overflow:hidden; background-color:#AFAFAF;}  
    </style>  
</head>  
<body>  
    <canvas id="canvas"></canvas>  
    <script>  
        var canvas = document.getElementById('canvas'),  
            context = canvas.getContext('2d');  
        canvas.width = document.body.clientWidth;  
        canvas.height = document.body.clientHeight;  
        context.lineWidth = 3;  
        context.strokeStyle = 'red';  
        context.arc(100, 100, 150, (Math.PI / 180) * 0, (Math.PI / 180) * 360, false);  
        context.clip();  
        context.beginPath();  
        context.arc(200, 200, 100, (Math.PI / 180) * 0, (Math.PI / 180) * 360, false);  
        context.stroke();  
        context.closePath();  
    </script>  
</body>  
</html>  

实际效果

应用save和restore完成只剪裁单独相对路径

<!DOCTYPE html>  
<html lang="en">  
<head>  
    <meta charset="UTF⑻">  
    <title></title>  
    <style>  
        *{margin:0; padding:0;}  
        html, body{width:100%; height:100%; overflow:hidden; background-color:#AFAFAF;}  
    </style>  
</head>  
<body>  
    <canvas id="canvas"></canvas>  
    <script>  
        var canvas = document.getElementById('canvas'),  
            context = canvas.getContext('2d');  
        canvas.width = document.body.clientWidth;  
        canvas.height = document.body.clientHeight;  
        context.lineWidth = 3;  
        context.strokeStyle = 'red';  
        context.save();  
        context.rect(0, 0, 200, 200);  
        context.clip();  
        context.beginPath();  
        context.arc(200, 200, 100, (Math.PI / 180) * 0, (Math.PI / 180) * 360, false);  
        context.stroke();  
        context.closePath();  
        context.restore();  
        context.beginPath();  
        context.arc(250, 250, 100, (Math.PI / 180) * 0, (Math.PI / 180) * 360, false);  
        context.stroke();  
        context.closePath();  
    </script>  
</body>  
</html>  

实际效果

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