圆形 circle
矩形 rect
椭圆 ellipse
线 line
折线 polyline
多边形 polygon
路径 path
可用于路径数据的命令
M = moveto L = lineto H = horizontal lineto V = vertical lineto C = curveto S = smooth curveto Q = quadratic Belzier curve T = smooth quadratic Belzier curveto A = elliptical Arc Z = closepath









