SECTION 4.4
225
Path Construction and Painting
A path is composed of straight and curved line segments, which may connect to
one another or may be disconnected. A pair of segments are said to
connect
only
if they are defined consecutively, with the second segment starting where the first
one ends. Thus, the order in which the segments of a path are defined is signifi-
cant. Nonconsecutive segments that meet or intersect fortuitously are not consid-
ered to connect.
A path is made up of one or more disconnected
subpaths,
each comprising a se-
quence of connected segments. The topology of the path is unrestricted: it may be
concave or convex, may contain multiple subpaths representing disjoint areas,
and may intersect itself in arbitrary ways. The
h
operator explicitly connects the
end of a subpath back to its starting point; such a subpath is said to be
closed.
A
subpath that has not been explicitly closed is
open.
As discussed in Section 4.1, “Graphics Objects,” a path object is defined by a se-
quence of operators to construct the path, followed by one or more operators to
paint the path or to use it as a clipping boundary. PDF path operators fall into
three categories:
•
Path construction operators
path is constructed by sequentially applying one or more of these operators.
•
Path-painting operators
object to be painted on the current page in any of a variety of ways.
•
Clipping path operators
painting operator, cause the path object also to be used for clipping of sub-
sequent graphics objects.
4.4.1 Path Construction Operators
A page description begins with an empty path and builds up its definition by in-
voking one or more path construction operators to add segments to it. The path
construction operators may be invoked in any sequence, but the first one invoked
must be
m
or
re
to begin a new subpath. The path definition concludes with the
application of a path-painting operator such as
S
,
f
, or
b
(see Section 4.4.2, “Path-
clipping path operators
W
or
W*
that the path construction operators do not place any marks on the page; only the
painting operators do that. A path definition is not complete until a path-painting
operator has been applied to it.