                        课程
                    
                        /前端开发
                        
                            /Html5
                        
                        /Canvas绘图详解

为什么使用了那个JS还是不能兼容IE？

<!DOCTYPE html>
<html>
    <head>
        <meta charset="UTF-8">
        <title>综合使用arc和arcTo绘制一轮弯月</title>
        <!--[if IE]><script type="text/javascript" src="js/excanvas.js"></script><![endif]-->
    </head>
    <body>
        <canvas id="canvas" style="margin: 0 auto; display: block; border: 1px solid #ddd;">
            当前浏览器不支持canvas画布，请更换浏览器之后再打开吧！
        </canvas>
        <br />
        <script type="text/javascript">
            window.onload=function(){
                var canvas = document.getElementById('canvas');
                canvas.width=800;
                canvas.height=800;
                var context = canvas.getContext('2d');
                
                context.arc(400,400,300,0.5*Math.PI,1.5*Math.PI,true);
                context.moveTo(400,100);
                context.arcTo(1200,400,400,700,(400-100)*dis(400,100,1200,400)/(1200-400));  // 把图画出来，根据同一个角的两个tan值相等可以算出来
                context.stroke();
            }
            
            function dis(x1,x2,y1,y2){
                return Math.sqrt((x1-x2)*(x1-x2)+(y1-y2)*(y1-y2));
            }
        </script>
    </body>
</html>

我是拿上次画的月亮的那个去做这个兼容，结果在谷歌上显示是这样的