CHAPTER 4
210
Graphics
4.3 Graphics State
A PDF consumer application maintains an internal data structure called the
graphics state
that holds current graphics control parameters. These parameters
define the global framework within which the graphics operators execute. For ex-
ample, the
f
(fill) operator implicitly uses the
current color
parameter, and the
S
(stroke) operator additionally uses the
current line width
parameter from the
graphics state.
The graphics state is initialized at the beginning of each page with the values
specified in Tables 4.2 and 4.3. Table 4.2 lists those graphics state parameters that
are device-independent and are appropriate to specify in page descriptions. The
parameters listed in Table 4.3 control details of the rendering (scan conversion)
process and are device-dependent; a page description that is intended to be de-
vice-independent should not modify these parameters.
TABLE 4.2 Device-independent graphics state parameters
PARAMETER
TYPE
VALUE
CTM
array
The
current transformation matrix,
which maps positions from user
coordinates to device coordinates (see Section 4.2, “Coordinate Sys-
nate transformation operator,
cm
. Initial value: a matrix that
transforms default user coordinates to device coordinates.
The
current clipping path,
which defines the boundary against
which all output is to be cropped (see Section 4.4.3, “Clipping Path
portion of the output page.
The
current color space
in which color values are to be interpreted
(see Section 4.5, “Color Spaces”). There are two separate color space
parameters: one for stroking and one for all other painting opera-
tions. Initial value:
DeviceGray
.
The
current color
to be used during painting operations (see Section
depend on the current color space; for most color spaces, a color
value consists of one to four numbers. There are two separate color
parameters: one for stroking and one for all other painting opera-
tions. Initial value: black.
clipping path
(internal)
color space
name or array
color
(various)