Graphics Reference
In-Depth Information
{ Constants }
RIGHTBDRY = 1;
TOPBDRY = 2;
LEFTBDRY = 4;
BOTTOMBDRY = 8;
boolean function
CS_Clip (
ref real
x0, y0, x1, y1;
real
xmin, ymin, xmax, ymax)
{ This function clips the segment from (x0, y0) to (x1, y1) against the window
[xmin, xmax]¥[ymin, ymax]. It returns
false
if the segment is entirely outside the
window and
true
otherwise. In the latter case the variables x0, y0, x1, and y1 will
also have been modified to specify the final clipped segment. }
begin
byte
c0, c1, c;
real
x, y;
{ First encode the points }
c0 := RegionCode (x0,y0);
c1 := RegionCode (x1,y1);
{ Next the main loop }
while
(c0
or
c1) π 0
do
if
(c0
and
c1) π 0
then
return
(
false
);
else
begin
{ Choose the first point not in the window }
c := c0;
if
c = 0
then
c := c1;
{ Now clip against line corresponding to first nonzero bit }
if
(LEFTBDRY
and
c) π 0
then
begin
{ Clip against left bdry }
x := xmin;
y := y0 + (y1 - y0)*(xmin - x0)/(x1 - x0);
end
else if
(RIGHTBDRY
and
c) π 0
then
begin
{ Clip against right bdry }
x := xmax;
y := y0 + (y1 -
y0)*(xmax x0)/(x1 - x0);
-
end
else if
(BOTTOMBDRY
and
c) π 0
then
Algorithm 3.2.1.1.
The Cohen-Sutherland line-clipping algorithm.
