一些基本绘画api

+ (instancetype)bezierPathWithRect:(CGRect)rect;

+ (instancetype)bezierPathWithOvalInRect:(CGRect)rect;

+ (instancetype)bezierPathWithRoundedRect:(CGRect)rect cornerRadius:(CGFloat)cornerRadius; 

// rounds all corners with the same horizontal and vertical radius

+ (instancetype)bezierPathWithRoundedRect:(CGRect)rect byRoundingCorners:(UIRectCorner)corners cornerRadii:(CGSize)cornerRadii;

+ (instancetype)bezierPathWithArcCenter:(CGPoint)center radius:(CGFloat)radius startAngle:(CGFloat)startAngle endAngle:(CGFloat)endAngle clockwise:(BOOL)clockwise;

+ (instancetype)bezierPathWithCGPath:(CGPathRef)CGPath;