Background

Clip boundaries are closed, non-self-intersecting, concave 2D polygons. Optional front and back Z clipping values can be assigned. The clip boundary is expressed in an arbitrary coordinate system relative to the objects being clipped.

In AutoCAD, when the user defines a clipping boundary for a block, the view direction and twist of the current view are used to define the coordinate system for the clip boundary. This might be the same as the coordinate system of the block reference being clipped. This is reflected in the API by the provision of a transformation to the clipping space from the block reference system:

Clip boundaries can be nested. A compound object can define a clipping boundary, and the objects that it contains can also define boundaries for their internal geometry. In this case, the nested geometry is first clipped against its parent's boundary and any resultant fragments are then clipped against the clip boundary of the outer block.