Changes to the drawing made by the entity data functions are reflected on the graphics screen, provided the entity being deleted, undeleted, modified, or created is in an area and on a layer that is currently visible.
There is one exception; when entmod modifies a subentity, it does not update the image of the entire (complex) entity. If, for example, an application modifies 100 vertices of an old-style polyline with 100 calls to entmod, the time required to recalculate and redisplay the entire polyline is unacceptably slow. Instead, an application can perform a series of subentity modifications, and then redisplay the entire entity with a single call to the entupd function.
Consider the following; if the first entity in the current drawing is an old-style polyline with several vertices, the following code modifies the second vertex of the polyline and regenerates its display.
(setq e1 (entnext)) ; Sets e1 to the polyline's entity name.
(setq v1 (entnext e1)) ; Sets v1 to its first vertex.
(setq v2 (entnext v1)) ; Sets v2 to its second vertex.
(setq v2d (entget v2)) ; Sets v2d to the vertex data.
(setq v2d
(subst
'(10 1.0 2.0 0.0)
(assoc 10 v2d) ; Changes the vertex's location in v2d
v2d ; to point (1,2,0).
)
)
(entmod v2d) ; Moves the vertex in the drawing.
(entupd e1) ; Regenerates the polyline entity e1.
The argument to entupd can specify either a main entity or a subentity. In either case, entupd regenerates the entire entity. Although its primary use is for complex entities, entupd can regenerate any entity in the current drawing.