/* Returns a transform that rotates by 'angle' radians about the vector
* '(x, y, z)'. If the vector has length zero the identity transform is
* returned. */
CA_EXTERN CATransform3D CATransform3DMakeRotation (CGFloat angle, CGFloat x,
CGFloat y, CGFloat z)
CA_AVAILABLE_STARTING (10.5, 2.0, 9.0, 2.0);
angle:旋转角度
后面的x,y,z三个值表示坐标系里面的一个点(x,y,z),原点与该点形成一条旋转轴