CHAPTER 4
338
Graphics
0
0
0
1
w
2
1
2
w-1
w
1
w-1
w+1
2w-1
h-1
(h-1)w
h
(h-1)w+1
hw-1
FIGURE 4.26
Source image coordinate system
0
0
w
(0, 1)
(1, 1)
CTM
h
(0, 0)
(1, 0)
Source image
Unit square
in user space
Current page
FIGURE 4.27
Mapping the source image
An image can be placed on the output page in any position, orientation, and size
by using the
cm
operator to modify the current transformation matrix (CTM) so
as to map the unit square of user space to the rectangle or parallelogram in which
the image is to be painted. Typically, this is done within a pair of
q
and
Q
opera-
tors to isolate the effect of the transformation, which can include translation, ro-