Svg drawing curve

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as well as ： http://www.cnblogs.com/netWild/archive/2010/12/07/1898792.html

It's worth noting that , When drawing an arc , An arc can be seen as part of an ellipse or a circle , A The first two parameters represent the length of the long and short semi axes of the ellipse , When the straight-line distance between two points is certain , The longer the distance between the long and short half axes , Then the curvature of this arc is smaller , The smoother it looks to the naked eye . This place needs attention .