html5 实现两个矩形的叠加_JavaScript

html5 实现两个矩形的叠加

<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="utf-8">
    <title>Canvas Primer - Example: Drawing shadows</title>
    <script type="text/javascript">
        window.addEventListener('load', function () {
                //得到canvas，并检测是否支持canvas
          var elem = document.getElementById('myCanvas');
          if (!elem || !elem.getContext) {
                return;
          }
 
          // 得到可以画图的上下文context
          var context = elem.getContext('2d');
          if (!context) {
                return;
          }
 
          // 分别设置阴影的偏移坐标，阴影的虚化程度，阴影的颜色，图形的填充颜色，以及绘制图形。
          context.shadowOffsetX = 10;
          context.shadowOffsetY = 10;
          context.shadowBlur    = 4;
          context.shadowColor   = 'red';
          context.fillStyle     = '#00f';
          context.fillRect(20, 20, 150, 100);
        }, false);
        </script>
          </head>
        <body>
    <p><canvas id="myCanvas" width="300" height="150">Your browser does not have 
    support for Canvas. </canvas></p>
  </body>
</html>