2 * Copyright (C) 1984-2017 Mark Nudelman
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.
7 * For more information, see the README file.
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.
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. }}
24 static POSITION *table = NULL; /* The position table */
25 static int table_size;
27 extern int sc_width, sc_height;
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
45 sindex = sc_height - 2;
48 sindex = sc_height - 1;
51 sindex = (sc_height - 1) / 2;
54 return (table[sindex]);
58 * Add a new file position to the bottom of the position table.
67 * Scroll the position table up.
69 for (i = 1; i < sc_height; i++)
70 table[i-1] = table[i];
71 table[sc_height - 1] = pos;
75 * Add a new file position to the top of the position table.
84 * Scroll the position table down.
86 for (i = sc_height - 1; i > 0; i--)
87 table[i] = table[i-1];
92 * Initialize the position table, done whenever we clear the screen.
99 for (i = 0; i < sc_height; i++)
100 table[i] = NULL_POSITION;
104 * Allocate or reallocate the position table.
109 struct scrpos scrpos;
111 if (sc_height <= table_size)
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.
119 get_scrpos(&scrpos, TOP);
122 scrpos.pos = NULL_POSITION;
123 table = (POSITION *) ecalloc(sc_height, sizeof(POSITION));
124 table_size = sc_height;
126 if (scrpos.pos != NULL_POSITION)
127 table[scrpos.ln-1] = scrpos.pos;
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.
143 for (i = 1; i < sc_height; i++)
150 * See if the entire screen is empty.
155 return (empty_lines(0, sc_height-1));
165 for (i = s; i <= e; i++)
166 if (table[i] != NULL_POSITION && table[i] != 0)
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.
180 get_scrpos(scrpos, where)
181 struct scrpos *scrpos;
190 case TOP: i = 0; dir = +1; last = sc_height-2; break;
191 default: i = sc_height-2; dir = -1; last = 0; break;
195 * Find the first line on the screen which has something on it,
196 * and return the screen line number and the file position.
200 if (table[i] != NULL_POSITION)
203 scrpos->pos = table[i];
206 if (i == last) break;
209 * The screen is empty.
211 scrpos->pos = NULL_POSITION;
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.
224 sindex_from_sline(sline)
228 * Negative screen line number means
229 * relative to the bottom of the screen.
234 * Can't be less than 1 or greater than sc_height.
238 if (sline > sc_height)
241 * Return zero-based line number, not one-based.