《JS原理、方法与实践》- canvas作图（八）- 阴影

属性值：

shadowOffsetX: 阴影的水平偏移距离
shadowOffsetY: 阴影的竖直偏移距离
shadowBlur: 阴影的模糊效果，数字越大越模糊
shadowColor: 阴影颜色

示例：

<!DOCTYPE html><html lang="en"><head>    <meta charset="UTF-8">    <meta name="viewport" content="width=device-width, initial-scale=1.0">    <title>Document</title></head><body>    <canvas id="c2d">浏览器不支持canvas</canvas>    <script>        const canvas = document.querySelector('#c2d');        if(canvas.getContext) {            const ctx = canvas.getContext('2d');                        // 设置阴影效果            ctx.shadowOffsetX = -7;            ctx.shadowOffsetY = 5;            ctx.shadowBlur = 3;            ctx.shadowColor = 'rgba(255,255,0,0.7)';                        ctx.fillStyle = 'red';            ctx.fillRect(15,30,130,40);        }    </script></body></html>