position.c revision 161475 
1/*
2 * Copyright (C) 1984-2004  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
25static POSITION *table = NULL;	/* The position table */
26static int table_size;
27
28extern 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
40position(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
61add_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
78add_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
95pos_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
107pos_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
136onscreen(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
153empty_screen()
154{
155	return (empty_lines(0, sc_height-1));
156}
157
158	public int
159empty_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
180get_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
212adjsline(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