1/*
2 * Copyright (C) 1984-2012  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
24static POSITION *table = NULL;	/* The position table */
25static int table_size;
26
27extern 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
39position(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
60add_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
77add_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
94pos_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
106pos_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
135onscreen(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
152empty_screen()
153{
154	return (empty_lines(0, sc_height-1));
155}
156
157	public int
158empty_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
179get_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
211adjsline(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