SECTION 4.4
227
Path Construction and Painting
OPERANDS
OPERATOR
DESCRIPTION
—
h
Close the current subpath by appending a straight line segment
from the current point to the starting point of the subpath. If the
current subpath is already closed,
h
does nothing.
This operator terminates the current subpath. Appending another
segment to the current path begins a new subpath, even if the new
segment begins at the endpoint reached by the
h
operation.
x y width height
re
Append a rectangle to the current path as a complete subpath, with
lower-left corner (
x
,
y
) and dimensions
width
and
height
in user
space. The operation
x y width height
re
is equivalent to
x y
m
(
x
+
width
)
y
l
(
x
+
width
) (
y
+
height
) l
x
(
y
+
height
) l
h
Cubic Bézier Curves
Curved path segments are specified as
cubic Bézier curves.
Such curves are de-
fined by four points: the two endpoints (the current point
P
0
and the final point
P
3
) and two
control points P
1
and
P
2
. Given the coordinates of the four points, the
curve is generated by varying the parameter
t
from 0.0 to 1.0 in the following
equation:
R
(
t
) =
(
1
–
t
)
P
0
+
3t
(
1
–
t
)
P
1
+
3t
(
1
–
t
)P
2
+
t P
3
When
t
=
0.0, the value of the function
R
(t) coincides with the current point
P
0
;
when
t
=
1.0,
R
(t) coincides with the final point
P
3
. Intermediate values of
t
gen-
erate intermediate points along the curve. The curve does not, in general, pass
through the two control points
P
1
and
P
2
.
3
2
2
3