.. role:: blue
   :class: blue

Copying a Set of Faces MbFaceShell
==================================
.. _Copying_a_Set_of_Faces_:

.. версия ядра: 

Each construction method that uses a set of faces in its input parameters, represented as :ref:`MbFaceShell <MbFaceShell_Set_of_Faces_>` or :ref:`MbSolid <MbSolid_Solid_Body_>`, modifies some vertices, edges, and faces of the source objects. To speed up constructions and keep the source face set unchanged, full or partial copying of :blue:`MbFaceShell` data is applied. The C3D geometric kernel uses four ways of copying a :blue:`MbFaceShell` face set, defined by the MbeCopyMode enumeration. As a rule, construction methods receive, together with the modified face set, a parameter of type MbeCopyMode that controls the transfer of faces, edges, and vertices from the source object to the constructed object.

Enumeration :blue:`MbeCopyMode` is declared in file *mb_enum.h*. A parameter of type :blue:`MbeCopyMode` can take one of four values: *cm_Copy*, *cm_KeepSurface*, *cm_KeepHistory*, *cm_Same*.

With value *cm_Copy*, the source face set of the modified object is fully copied, so the source object and the constructed object do not share surfaces, curves, faces, edges, vertices, or other objects. This option is used when the constructed object must not be linked to the source object.

With value *cm_KeepSurface*, the source object and the constructed object share the same base face surfaces. This option is used when high construction speed is required.

With value *cm_KeepHistory*, the source object and the constructed object share the same vertices, base face surfaces, and faces that are not modified by the performed construction or other operation. This option is used when maximum memory saving is required.

With value *cm_Same*, all necessary data of the source object are transferred to the constructed object, therefore after construction the source object must be deleted. This option is used when the source object is no longer needed and was created specifically for the performed construction.

Enumeration MbeCopyMode is used in the method for copying a face set :blue:`MbFaceShell` MbFaceShell::Copy( MbeCopyMode, MbShellHistory ). This method is used in solid construction operations whose input parameters include other solids.

With enumeration value *cm_Copy*, the source face set and its copy have no common data. The variant in which the source face set and its copy share common base surfaces corresponds to enumeration value *cm_KeepSurface*. The variant in which the source face set and its copy share common base surfaces, vertices, and faces not changed by the operation corresponds to enumeration value *cm_KeepHistory*. In this case, method :blue:`Copy`\(...) uses a pointer to object :blue:`MbShellHistory`, which stores the correspondence between the source face set and its copy. After the operation has been performed, the copy of the face set is passed as a parameter to method MbShellHistory:::blue:`SetOrigins`\( MbFaceShell & ) to replace unchanged faces in the copy with their originals from the source face set. The variant in which the face set is not copied in method :blue:`Copy`\(...) corresponds to enumeration value *cm_Same*. It should be noted that if the operation fails, the source face set will be modified.

To copy a face set :blue:`MbFaceShell`, method :blue:`Duplicate`\( MbRegDuplicate * iReg ) can be used. Object :blue:`MbRegDuplicate` is used to preserve in the copy the structure of mutual references that is present in the source face set. The copied face set and its copy will not be linked to each other.