If swept_object is a polygon, the sweep connects
n+1 successive copies of the closed polyline border of
the polygon to form body polygons exactly as though the border were a
swept polyline as described in Swept lines.
If there are m points in the
original polygon, then mn body polygons are formed by
this sweep. The body polygons form an extrusion of the boundary of the
original polygon with two holes at the open ends.
Finally, the sweep adds two copies of the original polygon to cover
the holes. We call these hole-filling polygons ends.
In this manner, sweep forms the boundary of a three-dimensional
object from a two-dimensional polygon.
The order of vertices of end polygons is important for correct culling as described above. An exact copy of the original polygon with vertex order intact forms the first end polygon. The other end polygon results from transforming and the reversing the order of vertices in the original. The transform places the original polygon at the uncovered hole; it is
T_1^n then T_2^n then ... then T_r^n.
If there are no options on the swept polygon, then the sweep
options are copied to each output polygon. If the swept polygon does
have options, these are copied to the ends; the sweep options are
copied to the body polygons. In this manner, body and ends may be
drawn with different characteristics such as fillcolor.