CHAPTER 4
4
Graphics
The graphics operators used in PDF content streams describe the appearance of
pages that are to be reproduced on a raster output device. The facilities described
in this chapter are intended for both printer and display applications.
The graphics operators form six main groups:
•
Graphics state operators
manipulate the data structure called the
graphics state,
the global framework within which the other graphics operators execute. The
graphics state includes the
current transformation matrix
(CTM), which maps
user space coordinates used within a PDF content stream into output device
coordinates. It also includes the
current color,
the
current clipping path,
and
many other parameters that are implicit operands of the painting operators.
•
Path construction operators
specify
paths,
which define shapes, line trajectories,
and regions of various sorts. They include operators for beginning a new path,
adding line segments and curves to it, and closing it.
•
Path-painting operators
fill a path with a color, paint a stroke along it, or use it
as a clipping boundary.
•
Other painting operators
paint certain self-describing graphics objects. These
include sampled images, geometrically defined shadings, and entire content
streams that in turn contain sequences of graphics operators.
•
Text operators
select and show
character glyphs
from
fonts
(descriptions of type-
faces for representing text characters). Because PDF treats glyphs as general
graphical shapes, many of the text operators could be grouped with the graph-
ics state or painting operators. However, the data structures and mechanisms
for dealing with glyph and font descriptions are sufficiently specialized that
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