1 /*
2 * Copyright (C) 1984-2017 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, see the README file.
8 */
9
10
11 /*
12 * Routines dealing with the "position" table.
13 * This is a table which tells the position (in the input file) of the
14 * first char on each currently displayed line.
15 *
16 * {{ The position table is scrolled by moving all the entries.
17 * Would be better to have a circular table
18 * and just change a couple of pointers. }}
19 */
20
21 #include "less.h"
22 #include "position.h"
23
24 static POSITION *table = NULL; /* The position table */
25 static int table_size;
26
27 extern int sc_width, sc_height;
28
29 /*
30 * Return the starting file position of a line displayed on the screen.
31 * The line may be specified as a line number relative to the top
32 * of the screen, but is usually one of these special cases:
33 * the top (first) line on the screen
34 * the second line on the screen
35 * the bottom line on the screen
36 * the line after the bottom line on the screen
37 */
38 public POSITION
position(sindex)39 position(sindex)
40 int sindex;
41 {
42 switch (sindex)
43 {
44 case BOTTOM:
45 sindex = sc_height - 2;
46 break;
47 case BOTTOM_PLUS_ONE:
48 sindex = sc_height - 1;
49 break;
50 case MIDDLE:
51 sindex = (sc_height - 1) / 2;
52 break;
53 }
54 return (table[sindex]);
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 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 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 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, TOP);
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 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 int i;
164
165 for (i = s; i <= e; i++)
166 if (table[i] != NULL_POSITION && table[i] != 0)
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,where)180 get_scrpos(scrpos, where)
181 struct scrpos *scrpos;
182 int where;
183 {
184 int i;
185 int dir;
186 int last;
187
188 switch (where)
189 {
190 case TOP: i = 0; dir = +1; last = sc_height-2; break;
191 default: i = sc_height-2; dir = -1; last = 0; break;
192 }
193
194 /*
195 * Find the first line on the screen which has something on it,
196 * and return the screen line number and the file position.
197 */
198 for (;; i += dir)
199 {
200 if (table[i] != NULL_POSITION)
201 {
202 scrpos->ln = i+1;
203 scrpos->pos = table[i];
204 return;
205 }
206 if (i == last) break;
207 }
208 /*
209 * The screen is empty.
210 */
211 scrpos->pos = NULL_POSITION;
212 }
213
214 /*
215 * Adjust a screen line number to be a simple positive integer
216 * in the range { 0 .. sc_height-2 }.
217 * (The bottom line, sc_height-1, is reserved for prompts, etc.)
218 * The given "sline" may be in the range { 1 .. sc_height-1 }
219 * to refer to lines relative to the top of the screen (starting from 1),
220 * or it may be in { -1 .. -(sc_height-1) } to refer to lines
221 * relative to the bottom of the screen.
222 */
223 public int
sindex_from_sline(sline)224 sindex_from_sline(sline)
225 int sline;
226 {
227 /*
228 * Negative screen line number means
229 * relative to the bottom of the screen.
230 */
231 if (sline < 0)
232 sline += sc_height;
233 /*
234 * Can't be less than 1 or greater than sc_height.
235 */
236 if (sline <= 0)
237 sline = 1;
238 if (sline > sc_height)
239 sline = sc_height;
240 /*
241 * Return zero-based line number, not one-based.
242 */
243 return (sline-1);
244 }
245