1 /*
2 * Copyright (C) 1984-2002 Mark Nudelman
3 *
4 * You may distribute under the terms of either the GNU General Public
5 * License or the Less License, as specified in the README file.
6 *
7 * For more information about less, or for information on how to
8 * contact the author, see the README file.
9 */
10
11
12 /*
13 * Routines dealing with the "position" table.
14 * This is a table which tells the position (in the input file) of the
15 * first char on each currently displayed line.
16 *
17 * {{ The position table is scrolled by moving all the entries.
18 * Would be better to have a circular table
19 * and just change a couple of pointers. }}
20 */
21
22 #include "less.h"
23 #include "position.h"
24
25 static POSITION *table = NULL; /* The position table */
26 static int table_size;
27
28 extern int sc_width, sc_height;
29
30 /*
31 * Return the starting file position of a line displayed on the screen.
32 * The line may be specified as a line number relative to the top
33 * of the screen, but is usually one of these special cases:
34 * the top (first) line on the screen
35 * the second line on the screen
36 * the bottom line on the screen
37 * the line after the bottom line on the screen
38 */
39 public POSITION
position(where)40 position(where)
41 int where;
42 {
43 switch (where)
44 {
45 case BOTTOM:
46 where = sc_height - 2;
47 break;
48 case BOTTOM_PLUS_ONE:
49 where = sc_height - 1;
50 break;
51 case MIDDLE:
52 where = (sc_height - 1) / 2;
53 }
54 return (table[where]);
55 }
56
57 /*
58 * Add a new file position to the bottom of the position table.
59 */
60 public void
add_forw_pos(pos)61 add_forw_pos(pos)
62 POSITION pos;
63 {
64 register int i;
65
66 /*
67 * Scroll the position table up.
68 */
69 for (i = 1; i < sc_height; i++)
70 table[i-1] = table[i];
71 table[sc_height - 1] = pos;
72 }
73
74 /*
75 * Add a new file position to the top of the position table.
76 */
77 public void
add_back_pos(pos)78 add_back_pos(pos)
79 POSITION pos;
80 {
81 register int i;
82
83 /*
84 * Scroll the position table down.
85 */
86 for (i = sc_height - 1; i > 0; i--)
87 table[i] = table[i-1];
88 table[0] = pos;
89 }
90
91 /*
92 * Initialize the position table, done whenever we clear the screen.
93 */
94 public void
pos_clear()95 pos_clear()
96 {
97 register int i;
98
99 for (i = 0; i < sc_height; i++)
100 table[i] = NULL_POSITION;
101 }
102
103 /*
104 * Allocate or reallocate the position table.
105 */
106 public void
pos_init()107 pos_init()
108 {
109 struct scrpos scrpos;
110
111 if (sc_height <= table_size)
112 return;
113 /*
114 * If we already have a table, remember the first line in it
115 * before we free it, so we can copy that line to the new table.
116 */
117 if (table != NULL)
118 {
119 get_scrpos(&scrpos);
120 free((char*)table);
121 } else
122 scrpos.pos = NULL_POSITION;
123 table = (POSITION *) ecalloc(sc_height, sizeof(POSITION));
124 table_size = sc_height;
125 pos_clear();
126 if (scrpos.pos != NULL_POSITION)
127 table[scrpos.ln-1] = scrpos.pos;
128 }
129
130 /*
131 * See if the byte at a specified position is currently on the screen.
132 * Check the position table to see if the position falls within its range.
133 * Return the position table entry if found, -1 if not.
134 */
135 public int
onscreen(pos)136 onscreen(pos)
137 POSITION pos;
138 {
139 register int i;
140
141 if (pos < table[0])
142 return (-1);
143 for (i = 1; i < sc_height; i++)
144 if (pos < table[i])
145 return (i-1);
146 return (-1);
147 }
148
149 /*
150 * See if the entire screen is empty.
151 */
152 public int
empty_screen()153 empty_screen()
154 {
155 return (empty_lines(0, sc_height-1));
156 }
157
158 public int
empty_lines(s,e)159 empty_lines(s, e)
160 int s;
161 int e;
162 {
163 register int i;
164
165 for (i = s; i <= e; i++)
166 if (table[i] != NULL_POSITION)
167 return (0);
168 return (1);
169 }
170
171 /*
172 * Get the current screen position.
173 * The screen position consists of both a file position and
174 * a screen line number where the file position is placed on the screen.
175 * Normally the screen line number is 0, but if we are positioned
176 * such that the top few lines are empty, we may have to set
177 * the screen line to a number > 0.
178 */
179 public void
get_scrpos(scrpos)180 get_scrpos(scrpos)
181 struct scrpos *scrpos;
182 {
183 register int i;
184
185 /*
186 * Find the first line on the screen which has something on it,
187 * and return the screen line number and the file position.
188 */
189 for (i = 0; i < sc_height; i++)
190 if (table[i] != NULL_POSITION)
191 {
192 scrpos->ln = i+1;
193 scrpos->pos = table[i];
194 return;
195 }
196 /*
197 * The screen is empty.
198 */
199 scrpos->pos = NULL_POSITION;
200 }
201
202 /*
203 * Adjust a screen line number to be a simple positive integer
204 * in the range { 0 .. sc_height-2 }.
205 * (The bottom line, sc_height-1, is reserved for prompts, etc.)
206 * The given "sline" may be in the range { 1 .. sc_height-1 }
207 * to refer to lines relative to the top of the screen (starting from 1),
208 * or it may be in { -1 .. -(sc_height-1) } to refer to lines
209 * relative to the bottom of the screen.
210 */
211 public int
adjsline(sline)212 adjsline(sline)
213 int sline;
214 {
215 /*
216 * Negative screen line number means
217 * relative to the bottom of the screen.
218 */
219 if (sline < 0)
220 sline += sc_height;
221 /*
222 * Can't be less than 1 or greater than sc_height-1.
223 */
224 if (sline <= 0)
225 sline = 1;
226 if (sline >= sc_height)
227 sline = sc_height - 1;
228 /*
229 * Return zero-based line number, not one-based.
230 */
231 return (sline-1);
232 }
233