canvas制作圆角矩形（包括填充矩形的功能）您的浏览器不支持 HTML5 canvas 标签。window.var m

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<head>
    <meta charset="utf-8">
    <title>canvas制作圆角矩形（包括填充矩形的功能）</title>
</head>

<body>
    <canvas id="myCanvas" style="border:1px solid #d3d3d3;">
        您的浏览器不支持 HTML5 canvas 标签。</canvas>
    <script>
    window.onload = function() {
        var myCanvas = document.getElementById("myCanvas"); //获取canvas对象  
        if (myCanvas.getContext("2d")) { //判断浏览器是否支持canvas标签  
            //设置canvas的宽度和高度  
            myCanvas.width = 400;
            myCanvas.height = 200;

            var context = myCanvas.getContext("2d"); //获取画布context的上下文环境  
            //绘制一个圆角矩形  
            strokeRoundRect(context, 10, 10, 100, 50, 10);  

            //绘制并填充一个圆角矩形  
            fillRoundRect(context, 200, 10, 100, 50, 10, 'rgba(0,0,0,0.7)');
        } else {
            alert("您的浏览器不支持canvas，请换个浏览器试试");
        }
    };


    /**该方法用来绘制一个有填充色的圆角矩形 
     *@param cxt:canvas的上下文环境 
     *@param x:左上角x轴坐标 
     *@param y:左上角y轴坐标 
     *@param width:矩形的宽度 
     *@param height:矩形的高度 
     *@param radius:圆的半径 
     *@param fillColor:填充颜色 
     **/
    function fillRoundRect(cxt, x, y, width, height, radius, /*optional*/ fillColor) {
        //圆的直径必然要小于矩形的宽高          
        if (2 * radius > width || 2 * radius > height) { return false; }

        cxt.save();
        cxt.translate(x, y);
        //绘制圆角矩形的各个边  
        drawRoundRectPath(cxt, width, height, radius);
        cxt.fillStyle = fillColor || "#000"; //若是给定了值就用给定的值否则给予默认值  
        cxt.fill();
        cxt.restore();
    }


    /**该方法用来绘制圆角矩形 
     *@param cxt:canvas的上下文环境 
     *@param x:左上角x轴坐标 
     *@param y:左上角y轴坐标 
     *@param width:矩形的宽度 
     *@param height:矩形的高度 
     *@param radius:圆的半径 
     *@param lineWidth:线条粗细 
     *@param strokeColor:线条颜色 
     **/
    function strokeRoundRect(cxt, x, y, width, height, radius, /*optional*/ lineWidth, /*optional*/ strokeColor) {
        //圆的直径必然要小于矩形的宽高          
        if (2 * radius > width || 2 * radius > height) { return false; }

        cxt.save();
        cxt.translate(x, y);
        //绘制圆角矩形的各个边  
        drawRoundRectPath(cxt, width, height, radius);
        cxt.lineWidth = lineWidth || 2; //若是给定了值就用给定的值否则给予默认值2  
        cxt.strokeStyle = strokeColor || "#000";
        cxt.stroke();
        cxt.restore();
    }

    function drawRoundRectPath(cxt, width, height, radius) {
        cxt.beginPath(0);
        //从右下角顺时针绘制，弧度从0到1/2PI  
        cxt.arc(width - radius, height - radius, radius, 0, Math.PI / 2);

        //矩形下边线  
        cxt.lineTo(radius, height);

        //左下角圆弧，弧度从1/2PI到PI  
        cxt.arc(radius, height - radius, radius, Math.PI / 2, Math.PI);

        //矩形左边线  
        cxt.lineTo(0, radius);

        //左上角圆弧，弧度从PI到3/2PI  
        cxt.arc(radius, radius, radius, Math.PI, Math.PI * 3 / 2);

        //上边线  
        cxt.lineTo(width - radius, 0);

        //右上角圆弧  
        cxt.arc(width - radius, radius, radius, Math.PI * 3 / 2, Math.PI * 2);

        //右边线  
        cxt.lineTo(width, height - radius);
        cxt.closePath();
    }
    </script>
</body>

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