HTML5 Canvas概述

替用内容

Because the <canvas> element is still relatively new and isn't implemented in some browsers (such as Firefox 1.0 and Internet Explorer), we need a means of providing fallback content when a browser doesn't support the element.

因为 <canvas> 相对较新，有些浏览器并没实现，如Firefox 1.0 和 Internet Explorer，所以我们需要为那些不支持canvas的浏览器提供替用显示内容。

Luckily this is very straightforward: we just provide alternative content inside the canvas element. Browsers who don't support it will ignore the element completely and render the fallback content, others will just render the canvas normally.
For instance we could provide a text description of the canvas content or provide a static image of the dynamically rendered content. This can look something like this:

我们只需要直接在canvas元素内插入替用内容即可。不支持canvas的浏览器会忽略canvas元素而直接渲染替用内容，而支持的浏览器则会正常地渲染canvas。例如，我们可以把一些文字或图片填入canvas内，作为替用内容：

<canvas id="stockGraph" width="150" height="150">
  current stock price: $3.15 +0.15
</canvas>

<canvas id="clock" width="150" height="150">
  <img src="images/clock.png" width="150" height="150"/>
</canvas>




结束标签 </canvas> 是必须的
In the Apple Safari implementation, <canvas> is an element implemented in much the same way <img> is; it does not have an end tag. However, for <canvas> to have widespread use on the web, some facility for fallback content must be provided. Therefore, Mozilla's implementation requires an end tag (</canvas>).
在Apple Safari里，<canvas>的实现跟<img>很相似，它并不没有结束标签。然而，为了使 <canvas> 能在web的世界里广泛适用，需要给替用内容提供一个容身之所，因此，在Mozilla的实现里结束标签(</canvas>)是必须的。
If fallback content is not needed, a simple <canvas id="foo" ...></canvas> will be fully compatible with both Safari and Mozilla -- Safari will simply ignore the end tag.								 
 2/4   首页 上一页 1 2 3 4 下一页 尾页