利用前者填充边自相交的多边形区域需要做大量排序操作，这极大降低了填充效率；
But using the former to fill polygons with edge self-intersection needs large of taxes, affecting filling efficiency greatly.
有两种抽象层：硬件抽象层及平台抽象层，前者的必要性显而易见，而后者的目的是充分利用平台所提供的最佳特性。
There are two kinds of abstraction layers: a hardware one, and its necessity is obvious, then there is a platform abstraction layer to make use of the best features a platform provides.
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