核心函数是:CGContextAddArc(CGContextRef c, CGFloat x, CGFloat y, CGFloat radius, CGFloat startAngle, CGFloat endAngle, int clockwise)CGContextAddArc(CGContextRef c, CGFloat x
核心函数是:CGContextAddArc(CGContextRef c, CGFloat x, CGFloat y, CGFloat radius, CGFloat startAngle, CGFloat endAngle, int clockwise)CGContextAddArc(CGContextRef c, CGFloat x