Lesson1/demo9.html

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Canvas实战－五角星</title>
</head>
<body>
<canvas id="canvas" style="border: 1px solid #555;display: block;margin:50px auto;"></canvas>
<script>
    window.onload = function () {
        var canvas = document.getElementById("canvas");
        canvas.width = 500;
        canvas.height = 500;
        var context = canvas.getContext("2d");

        context.lineWidth = 5;
        context.strokeStyle = "#CC4A3C";

        drawStar(context, 200, 100, 250, 250);

    };
    function drawStar(cxt, R, r, x, y) {
        cxt.beginPath();
        for (var i = 0; i < 5; i++) {
            //绘制大圆上的五个坐标点
            cxt.lineTo(Math.cos((18 + i * 72) / 180 * Math.PI) * R + x,
                    -Math.sin((18 + i * 72) / 180 * Math.PI) * R + y);
            //绘制小圆上的五个坐标点
            cxt.lineTo(Math.cos((54 + i * 72) / 180 * Math.PI) * r + x,
                    -Math.sin((54 + i * 72) / 180 * Math.PI) * r + y);
        }
        cxt.closePath();
        cxt.stroke();
    }
</script>
</body>
</html>