Frame里的网页不能透明？

奇怪，Frame类有个Opacity属性，设置其值为0.2一点反应都没有，又貌似没有其他属性可以设置透明度，难道是bug？如果是这样，那么Frame肯定是不能实现有透明度变化的动画了……

用Google搜了一下，找到这样两个帖子：

The animation worked when applied on other elements in a test project I made, including a Frame element with just a solid red background. I think it’s just a limitation of the Frame element when rendering HTML. It uses the WebBrowser control which is just a wrapper around the MSHTML ActiveX control, I believe.

Hmm, it might be fun to write a Web browser in WPF…

Frame element is wrapping window with handle, thus it can not have animated opacity. However, you can create VisualBrush over Frame and Animate it

看来对HTML页面是真的没办法了，自己另外想办法实现咯:(