一个简单的脚本来模拟雨滴落在玻璃表面效果。rainyday.js拥有功能可扩展的API，碰撞检测，并很容易用自己不同的动画组件实现扩展。Rainyday.js是一个纯的JavaScript库，用到了HTML5的特性，所以都支持大多数现代浏览器它。

How to use:    var engine = new RainyDay({      element: image,         // Image element                              // This value is required      parentElement: someDiv, // Element to be used as a parent for the canvas                              // If not provided assuming the 'body' element      crop: [0, 0, 50, 60],   // Coordinates if only a part of the image should be used                              // If not provided entire image will be used      blur: 10,               // Defines blur due to rain effect                              // Assuming 10 if not provided                              // Use 0 value to disable the blur      opacity: 1              // Opacity of rain drops                              // Assuming 1 if not provided  });  engine.rain(      [          [1, 0, 20],         // add 20 drops of size 1...          [3, 3, 1]           // ... and 1 drop of size from 3 - 6 ...      ],                             100);        

项目主页：http://www.open-open.com/lib/view/home/1406863000218