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
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
|
/* $Xorg: lines.c,v 1.3 2000/08/17 19:46:30 cpqbld Exp $ */
/* Copyright International Business Machines, Corp. 1991
* All Rights Reserved
* Copyright Lexmark International, Inc. 1991
* All Rights Reserved
*
* License to use, copy, modify, and distribute this software and its
* documentation for any purpose and without fee is hereby granted,
* provided that the above copyright notice appear in all copies and that
* both that copyright notice and this permission notice appear in
* supporting documentation, and that the name of IBM or Lexmark not be
* used in advertising or publicity pertaining to distribution of the
* software without specific, written prior permission.
*
* IBM AND LEXMARK PROVIDE THIS SOFTWARE "AS IS", WITHOUT ANY WARRANTIES OF
* ANY KIND, EITHER EXPRESS OR IMPLIED, INCLUDING, BUT NOT LIMITED TO ANY
* IMPLIED WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE,
* AND NONINFRINGEMENT OF THIRD PARTY RIGHTS. THE ENTIRE RISK AS TO THE
* QUALITY AND PERFORMANCE OF THE SOFTWARE, INCLUDING ANY DUTY TO SUPPORT
* OR MAINTAIN, BELONGS TO THE LICENSEE. SHOULD ANY PORTION OF THE
* SOFTWARE PROVE DEFECTIVE, THE LICENSEE (NOT IBM OR LEXMARK) ASSUMES THE
* ENTIRE COST OF ALL SERVICING, REPAIR AND CORRECTION. IN NO EVENT SHALL
* IBM OR LEXMARK BE LIABLE FOR ANY SPECIAL, INDIRECT OR CONSEQUENTIAL
* DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR
* PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS
* ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF
* THIS SOFTWARE.
*/
/* LINES CWEB V0003 ******** */
/*
:h1.LINES Module - Rasterizing Lines
&author. Duaine W. Pryor, Jr. and Jeffrey B. Lotspiech (lotspiech@almaden.ibm.com)
:h3.Include Files
The included files are:
*/
#include "objects.h"
#include "spaces.h"
#include "regions.h"
#include "lines.h"
/*
:h3.Functions Provided to the TYPE1IMAGER User
None.
*/
/*
:h3.Functions Provided to Other Modules
This module provides the following entry point to other modules:
*/
/*SHARED LINE(S) ORIGINATED HERE*/
/*
:h3.Macros Provided to Other Modules
None.
*/
/*
:h2.StepLine() - Produces Run Ends for a Line After Checks
The main work is done by Bresenham(); here we just perform checks and
get the line so that its Y direction is always increasing:
*/
void StepLine(R, x1, y1, x2, y2)
register struct region *R; /* region being built */
register fractpel x1,y1; /* starting point */
register fractpel x2,y2; /* ending point */
{
register fractpel dy;
IfTrace4((LineDebug > 0), ".....StepLine: (%p,%p) to (%p,%p)\n",
x1, y1, x2, y2);
dy = y2 - y1;
/*
We execute the "GOING_TO" macro to call back the REGIONS module, if
necessary (like if the Y direction of the edge has changed):
*/
GOING_TO(R, x1, y1, x2, y2, dy);
if (dy == 0)
return;
if (dy < 0)
Bresenham(R->edge, x2, y2, x1, y1);
else
Bresenham(R->edge, x1, y1, x2, y2);
return;
}
/*
:h3.Bresenham() - Actually Produces Run Ends
This routine runs a Bresenham line-stepping
algorithm. See, for example, Newman and Sproul, :hp1/Principles
of Interactive Computer Graphics/, pp. 25-27.
When we enter this, we
are guaranteed that dy is positive.
We'd like to work in 8 bit precision, so we'll define some macros and
constants to let us do that:
*/
#define PREC 8 /* we'll keep fraction pels in 8 bit precision */
/*
RoundFP() rounds down by 'b' bits:
*/
#define RoundFP(xy,b) (((xy)+(1<<((b)-1)))>>(b))
/*
TruncFP() truncates down by 'b' bits:
*/
#define TruncFP(xy,b) ((xy)>>(b))
void Bresenham(edgeP,x1,y1,x2,y2)
register pel *edgeP; /* pointer to top of list (y == 0) */
register fractpel x1,y1; /* starting point on line */
register fractpel x2,y2; /* ending point on the line (down) */
{
register long dx,dy; /* change in x and y, in my own precision */
register long x,y; /* integer pel starting point */
register int count; /* integer pel delta y */
register long d; /* the Bresenham algorithm error term */
x1 = TruncFP(x1, FRACTBITS-PREC);
y1 = TruncFP(y1, FRACTBITS-PREC);
x2 = TruncFP(x2, FRACTBITS-PREC);
y2 = TruncFP(y2, FRACTBITS-PREC);
dx = x2 - x1;
dy = y2 - y1;
/*
Find the starting x and y integer pel coordinates:
*/
x = RoundFP(x1,PREC);
y = RoundFP(y1,PREC);
edgeP += y;
count = RoundFP(y2,PREC) - y;
/*------------------------------------------------------------------*/
/* Force dx to be positive so that dfy will be negative */
/* this means that vertical moves will decrease d */
/*------------------------------------------------------------------*/
if (dx<0)
{
dx = -dx;
#define P PREC
d=(dy*(x1-(x<<P)+(1<<(P-1)))-dx*((y<<P)-y1+(1<<(P-1))))>>P;
#undef P
while(--count >= 0 )
{
while(d<0)
{
--x;
d += dy;
}
*(edgeP++) = x;
d -= dx;
}
}
else /* positive dx */
{
#define P PREC
d = (dy*((x<<P)-x1+(1<<(P-1)))-dx*((y<<P)-y1+(1<<(P-1))))>>P;
#undef P
while(--count >= 0 )
{
while(d<0)
{
++x;
d += dy;
}
*(edgeP++) = x;
d -= dx;
}
}
}
|
