IMesh::FaceReverseOrder

Reverses the order in which the face references its vertices. The face will essentially become its backface.

   HRESULT FaceReverseOrder(
   DWORD flags,  
   BOOL bAll  

);

flags

[in] A value of 0 will show the progress dialog with a cancel button, a value of 1 will remove the cancel button.

bAll

[in] A non-zero value will perform the operation on the entire mesh, otherwise the operation applies to only the selection.