html5画布元素和svg
问题描述：
为什么我们需要html5 canvas元素，同样可以通过嵌入式svg实现？
Why do we need the html5 canvas element, when the same can be achieved through embedded svg?
答
SVG和canvas并非真正可互换的技术。 SVG是一种保留模式图形，其中所有内容都是从相当抽象的模型（SVG文档）中提取的。另一方面，Canvas是一种立即模式图形，没有模型，客户端（JavaScript）必须处理重绘，动画等。
SVG and canvas aren't really interchangeable technologies. SVG is a type of retained mode graphics where everything is drawn from a rather abstract model (the SVG document). Canvas on the other hand is a kind of immediate mode graphics, where there is no model and the client (JavaScript) must take care of redrawing, animations etc.