Clipping is the exclusion of those primitives, or parts of primitives,
which lie outside a specified window or viewport. That is to say, if
clipping to a particular window is enabled, then only those parts of
primitives which lie within the boundaries of the window will be
displayed. Both the normalization transformation viewport (in NDC space)
and the workstation window can be used to clip a picture.
Clipping at the boundary of the normalization transformation viewport
(clipping rectangle) effects the image displayed on ALL workstations.
However, clipping at the boundary of the
workstation window only affects the image on the display surface
belonging to that particular workstation.
This is illustrated in Workstation Viewport 1 in 
.
The application can control whether clipping at the boundary of the clipping rectangle is enabled or not by calling the routine GSCLIP(VAL). This routine takes the value 'GNCLIP' (no clip) or 'GCLIP' (clip), and the default is to clip. Clipping at the workstation window may not be switched off.