1 /*
2 * Copyright (C) 1984-2015 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(where)39 position(where)
40 int where;
41 {
42 switch (where)
43 {
44 case BOTTOM:
45 where = sc_height - 2;
46 break;
47 case BOTTOM_PLUS_ONE:
48 where = sc_height - 1;
49 break;
50 case MIDDLE:
51 where = (sc_height - 1) / 2;
52 }
53 return (table[where]);
54 }
55
56 /*
57 * Add a new file position to the bottom of the position table.
58 */
59 public void
add_forw_pos(pos)60 add_forw_pos(pos)
61 POSITION pos;
62 {
63 register int i;
64
65 /*
66 * Scroll the position table up.
67 */
68 for (i = 1; i < sc_height; i++)
69 table[i-1] = table[i];
70 table[sc_height - 1] = pos;
71 }
72
73 /*
74 * Add a new file position to the top of the position table.
75 */
76 public void
add_back_pos(pos)77 add_back_pos(pos)
78 POSITION pos;
79 {
80 register int i;
81
82 /*
83 * Scroll the position table down.
84 */
85 for (i = sc_height - 1; i > 0; i--)
86 table[i] = table[i-1];
87 table[0] = pos;
88 }
89
90 /*
91 * Initialize the position table, done whenever we clear the screen.
92 */
93 public void
pos_clear()94 pos_clear()
95 {
96 register int i;
97
98 for (i = 0; i < sc_height; i++)
99 table[i] = NULL_POSITION;
100 }
101
102 /*
103 * Allocate or reallocate the position table.
104 */
105 public void
pos_init()106 pos_init()
107 {
108 struct scrpos scrpos;
109
110 if (sc_height <= table_size)
111 return;
112 /*
113 * If we already have a table, remember the first line in it
114 * before we free it, so we can copy that line to the new table.
115 */
116 if (table != NULL)
117 {
118 get_scrpos(&scrpos);
119 free((char*)table);
120 } else
121 scrpos.pos = NULL_POSITION;
122 table = (POSITION *) ecalloc(sc_height, sizeof(POSITION));
123 table_size = sc_height;
124 pos_clear();
125 if (scrpos.pos != NULL_POSITION)
126 table[scrpos.ln-1] = scrpos.pos;
127 }
128
129 /*
130 * See if the byte at a specified position is currently on the screen.
131 * Check the position table to see if the position falls within its range.
132 * Return the position table entry if found, -1 if not.
133 */
134 public int
onscreen(pos)135 onscreen(pos)
136 POSITION pos;
137 {
138 register int i;
139
140 if (pos < table[0])
141 return (-1);
142 for (i = 1; i < sc_height; i++)
143 if (pos < table[i])
144 return (i-1);
145 return (-1);
146 }
147
148 /*
149 * See if the entire screen is empty.
150 */
151 public int
empty_screen()152 empty_screen()
153 {
154 return (empty_lines(0, sc_height-1));
155 }
156
157 public int
empty_lines(s,e)158 empty_lines(s, e)
159 int s;
160 int e;
161 {
162 register int i;
163
164 for (i = s; i <= e; i++)
165 if (table[i] != NULL_POSITION && table[i] != 0)
166 return (0);
167 return (1);
168 }
169
170 /*
171 * Get the current screen position.
172 * The screen position consists of both a file position and
173 * a screen line number where the file position is placed on the screen.
174 * Normally the screen line number is 0, but if we are positioned
175 * such that the top few lines are empty, we may have to set
176 * the screen line to a number > 0.
177 */
178 public void
get_scrpos(scrpos)179 get_scrpos(scrpos)
180 struct scrpos *scrpos;
181 {
182 register int i;
183
184 /*
185 * Find the first line on the screen which has something on it,
186 * and return the screen line number and the file position.
187 */
188 for (i = 0; i < sc_height; i++)
189 if (table[i] != NULL_POSITION)
190 {
191 scrpos->ln = i+1;
192 scrpos->pos = table[i];
193 return;
194 }
195 /*
196 * The screen is empty.
197 */
198 scrpos->pos = NULL_POSITION;
199 }
200
201 /*
202 * Adjust a screen line number to be a simple positive integer
203 * in the range { 0 .. sc_height-2 }.
204 * (The bottom line, sc_height-1, is reserved for prompts, etc.)
205 * The given "sline" may be in the range { 1 .. sc_height-1 }
206 * to refer to lines relative to the top of the screen (starting from 1),
207 * or it may be in { -1 .. -(sc_height-1) } to refer to lines
208 * relative to the bottom of the screen.
209 */
210 public int
adjsline(sline)211 adjsline(sline)
212 int sline;
213 {
214 /*
215 * Negative screen line number means
216 * relative to the bottom of the screen.
217 */
218 if (sline < 0)
219 sline += sc_height;
220 /*
221 * Can't be less than 1 or greater than sc_height-1.
222 */
223 if (sline <= 0)
224 sline = 1;
225 if (sline >= sc_height)
226 sline = sc_height - 1;
227 /*
228 * Return zero-based line number, not one-based.
229 */
230 return (sline-1);
231 }
232