1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
|
{
This file is part of the Free Pascal run time library.
Copyright (c) 1999-2000 by the Free Pascal development team
This include implements the different clipping algorithms
See the file COPYING.FPC, included in this distribution,
for details about the copyright.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
**********************************************************************}
const
LEFT = 1; { Left window }
RIGHT = 2; { Right window }
BOTTOM = 4; { Bottom window }
TOP = 8; { Top window }
{ 0 = in window }
function LineClipped(var x1, y1,x2,y2: smallint; xmin, ymin,
xmax, ymax:smallint): boolean;
{********************************************************}
{ Function LineClipped() }
{--------------------------------------------------------}
{ This routine clips the line coordinates to the }
{ min. and max. values of the window. Returns TRUE if }
{ the ENTIRE line was clipped. Updated }
{ clipped line endpoints are also returned. }
{ This algorithm is the classic Cohen-Sutherland line }
{ clipping algorithm. }
{--------------------------------------------------------}
var
code1, code2: longint;
code: longint;
newx,newy: smallint;
done:boolean;
function outcode(x,y:smallint): longint;
{********************************************************}
{ Function OutCode() }
{--------------------------------------------------------}
{ This routine determines if the specified end point }
{ of a line lies within the visible window, if not it }
{ determines in which window the point is. }
{--------------------------------------------------------}
var
code: longint;
begin
code := 0;
if (x<xmin) then
code:=code or LEFT
else if (x>xmax) then
code:=code or RIGHT;
if (y>ymax) then
code:=code or BOTTOM
else if (y<ymin) then
code:=code or TOP;
outcode:=code;
end;
begin
done:=false;
code1:= OutCode(x1,y1);
code2:= OutCode(x2,y2);
while not done do
begin
{ Accept trivially }
{ both points are in window }
if ((code1=0) and (code2=0)) then
begin
done:=TRUE;
LineClipped:=FALSE;
exit;
end
else
{ Reject trivially }
{ Neither points are in window }
if (code1 and code2) <> 0 then
begin
done:=true;
LineClipped:=TRUE;
exit;
end
else
begin
{ Some points are partially out of the window }
{ find the new end point of the lines... }
if code1 = 0 then
code:=code2
else
code:=code1;
if (code and LEFT) <> 0 then
begin
newy:=y1+((y2-y1)*(xmin-x1)) div (x2-x1);
newx:=xmin;
end
else
if (code and RIGHT) <> 0 then
begin
newy:=y1+((y2-y1)*(xmax-x1)) div (x2-x1);
newx:=xmax;
end
else
if (code and BOTTOM) <> 0 then
begin
newx:=x1+((x2-x1)*(ymax-y1)) div (y2-y1);
newy:=ymax;
end
else
if (code and TOP) <> 0 then
begin
newx:=x1+((x2-x1)*(ymin-y1)) div (y2-y1);
newy:=ymin;
end;
if (code1 = code) then
begin
x1 := newx; y1:= newy;
code1:=outcode(x1,y1)
end
else
begin
x2:= newx; y2:= newy;
code2:=outcode(x2,y2);
end
end;
end;
LineClipped:=FALSE;
end;
|
