Integrate custom entity with the lengthen command

By Augusto Goncalves

The LENGTHEN command can only work with the following classes, or any custom classes derived from them:

AcDbLine
AcDbArc
AcDbCircle
AcDb2dPolyline
AcDb3dPolyline
AcDbEllipse
AcDbSpline
AcDbPolyline

If the custom entity is derived from any of these, LENGTHEN will automatically work, but if not, unfortunately there is nothing we can do to implement the command.