1/*
2 * Copyright (C) 1984-2007  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 * Primitives for displaying the file on the screen,
14 * scrolling either forward or backward.
15 */
16
17#include "less.h"
18#include "position.h"
19
20public int hit_eof;	/* Keeps track of how many times we hit end of file */
21public int screen_trashed;
22public int squished;
23public int no_back_scroll = 0;
24public int forw_prompt;
25
26extern int sigs;
27extern int top_scroll;
28extern int quiet;
29extern int sc_width, sc_height;
30extern int plusoption;
31extern int forw_scroll;
32extern int back_scroll;
33extern int ignore_eoi;
34extern int clear_bg;
35extern int final_attr;
36extern int oldbot;
37#if TAGS
38extern char *tagoption;
39#endif
40
41/*
42 * Sound the bell to indicate user is trying to move past end of file.
43 */
44	static void
45eof_bell()
46{
47	if (quiet == NOT_QUIET)
48		bell();
49	else
50		vbell();
51}
52
53/*
54 * Check to see if the end of file is currently "displayed".
55 */
56	static void
57eof_check()
58{
59	POSITION pos;
60
61	if (ignore_eoi)
62		return;
63	if (ABORT_SIGS())
64		return;
65	/*
66	 * If the bottom line is empty, we are at EOF.
67	 * If the bottom line ends at the file length,
68	 * we must be just at EOF.
69	 */
70	pos = position(BOTTOM_PLUS_ONE);
71	if (pos == NULL_POSITION || pos == ch_length())
72		hit_eof++;
73}
74
75/*
76 * If the screen is "squished", repaint it.
77 * "Squished" means the first displayed line is not at the top
78 * of the screen; this can happen when we display a short file
79 * for the first time.
80 */
81	public void
82squish_check()
83{
84	if (!squished)
85		return;
86	squished = 0;
87	repaint();
88}
89
90/*
91 * Display n lines, scrolling forward,
92 * starting at position pos in the input file.
93 * "force" means display the n lines even if we hit end of file.
94 * "only_last" means display only the last screenful if n > screen size.
95 * "nblank" is the number of blank lines to draw before the first
96 *   real line.  If nblank > 0, the pos must be NULL_POSITION.
97 *   The first real line after the blanks will start at ch_zero().
98 */
99	public void
100forw(n, pos, force, only_last, nblank)
101	register int n;
102	POSITION pos;
103	int force;
104	int only_last;
105	int nblank;
106{
107	int eof = 0;
108	int nlines = 0;
109	int do_repaint;
110	static int first_time = 1;
111
112	squish_check();
113
114	/*
115	 * do_repaint tells us not to display anything till the end,
116	 * then just repaint the entire screen.
117	 * We repaint if we are supposed to display only the last
118	 * screenful and the request is for more than a screenful.
119	 * Also if the request exceeds the forward scroll limit
120	 * (but not if the request is for exactly a screenful, since
121	 * repainting itself involves scrolling forward a screenful).
122	 */
123	do_repaint = (only_last && n > sc_height-1) ||
124		(forw_scroll >= 0 && n > forw_scroll && n != sc_height-1);
125
126	if (!do_repaint)
127	{
128		if (top_scroll && n >= sc_height - 1 && pos != ch_length())
129		{
130			/*
131			 * Start a new screen.
132			 * {{ This is not really desirable if we happen
133			 *    to hit eof in the middle of this screen,
134			 *    but we don't yet know if that will happen. }}
135			 */
136			pos_clear();
137			add_forw_pos(pos);
138			force = 1;
139			clear();
140			home();
141		}
142
143		if (pos != position(BOTTOM_PLUS_ONE) || empty_screen())
144		{
145			/*
146			 * This is not contiguous with what is
147			 * currently displayed.  Clear the screen image
148			 * (position table) and start a new screen.
149			 */
150			pos_clear();
151			add_forw_pos(pos);
152			force = 1;
153			if (top_scroll)
154			{
155				clear();
156				home();
157			} else if (!first_time)
158			{
159				putstr("...skipping...\n");
160			}
161		}
162	}
163
164	while (--n >= 0)
165	{
166		/*
167		 * Read the next line of input.
168		 */
169		if (nblank > 0)
170		{
171			/*
172			 * Still drawing blanks; don't get a line
173			 * from the file yet.
174			 * If this is the last blank line, get ready to
175			 * read a line starting at ch_zero() next time.
176			 */
177			if (--nblank == 0)
178				pos = ch_zero();
179		} else
180		{
181			/*
182			 * Get the next line from the file.
183			 */
184			pos = forw_line(pos);
185			if (pos == NULL_POSITION)
186			{
187				/*
188				 * End of file: stop here unless the top line
189				 * is still empty, or "force" is true.
190				 * Even if force is true, stop when the last
191				 * line in the file reaches the top of screen.
192				 */
193				eof = 1;
194				if (!force && position(TOP) != NULL_POSITION)
195					break;
196				if (!empty_lines(0, 0) &&
197				    !empty_lines(1, 1) &&
198				     empty_lines(2, sc_height-1))
199					break;
200			}
201		}
202		/*
203		 * Add the position of the next line to the position table.
204		 * Display the current line on the screen.
205		 */
206		add_forw_pos(pos);
207		nlines++;
208		if (do_repaint)
209			continue;
210		/*
211		 * If this is the first screen displayed and
212		 * we hit an early EOF (i.e. before the requested
213		 * number of lines), we "squish" the display down
214		 * at the bottom of the screen.
215		 * But don't do this if a + option or a -t option
216		 * was given.  These options can cause us to
217		 * start the display after the beginning of the file,
218		 * and it is not appropriate to squish in that case.
219		 */
220		if (first_time && pos == NULL_POSITION && !top_scroll &&
221#if TAGS
222		    tagoption == NULL &&
223#endif
224		    !plusoption)
225		{
226			squished = 1;
227			continue;
228		}
229		put_line();
230#if 0
231		/* {{
232		 * Can't call clear_eol here.  The cursor might be at end of line
233		 * on an ignaw terminal, so clear_eol would clear the last char
234		 * of the current line instead of all of the next line.
235		 * If we really need to do this on clear_bg terminals, we need
236		 * to find a better way.
237		 * }}
238		 */
239		if (clear_bg && apply_at_specials(final_attr) != AT_NORMAL)
240		{
241			/*
242			 * Writing the last character on the last line
243			 * of the display may have scrolled the screen.
244			 * If we were in standout mode, clear_bg terminals
245			 * will fill the new line with the standout color.
246			 * Now we're in normal mode again, so clear the line.
247			 */
248			clear_eol();
249		}
250#endif
251		forw_prompt = 1;
252	}
253
254	if (ignore_eoi)
255		hit_eof = 0;
256	else if (eof && !ABORT_SIGS())
257		hit_eof++;
258	else
259		eof_check();
260	if (nlines == 0)
261		eof_bell();
262	else if (do_repaint)
263		repaint();
264	first_time = 0;
265	(void) currline(BOTTOM);
266}
267
268/*
269 * Display n lines, scrolling backward.
270 */
271	public void
272back(n, pos, force, only_last)
273	register int n;
274	POSITION pos;
275	int force;
276	int only_last;
277{
278	int nlines = 0;
279	int do_repaint;
280
281	squish_check();
282	do_repaint = (n > get_back_scroll() || (only_last && n > sc_height-1));
283	hit_eof = 0;
284	while (--n >= 0)
285	{
286		/*
287		 * Get the previous line of input.
288		 */
289		pos = back_line(pos);
290		if (pos == NULL_POSITION)
291		{
292			/*
293			 * Beginning of file: stop here unless "force" is true.
294			 */
295			if (!force)
296				break;
297		}
298		/*
299		 * Add the position of the previous line to the position table.
300		 * Display the line on the screen.
301		 */
302		add_back_pos(pos);
303		nlines++;
304		if (!do_repaint)
305		{
306			home();
307			add_line();
308			put_line();
309		}
310	}
311
312	eof_check();
313	if (nlines == 0)
314		eof_bell();
315	else if (do_repaint)
316		repaint();
317	else if (!oldbot)
318		lower_left();
319	(void) currline(BOTTOM);
320}
321
322/*
323 * Display n more lines, forward.
324 * Start just after the line currently displayed at the bottom of the screen.
325 */
326	public void
327forward(n, force, only_last)
328	int n;
329	int force;
330	int only_last;
331{
332	POSITION pos;
333
334	if (get_quit_at_eof() && hit_eof && !(ch_getflags() & CH_HELPFILE))
335	{
336		/*
337		 * If the -e flag is set and we're trying to go
338		 * forward from end-of-file, go on to the next file.
339		 */
340		if (edit_next(1))
341			quit(QUIT_OK);
342		return;
343	}
344
345	pos = position(BOTTOM_PLUS_ONE);
346	if (pos == NULL_POSITION && (!force || empty_lines(2, sc_height-1)))
347	{
348		if (ignore_eoi)
349		{
350			/*
351			 * ignore_eoi is to support A_F_FOREVER.
352			 * Back up until there is a line at the bottom
353			 * of the screen.
354			 */
355			if (empty_screen())
356				pos = ch_zero();
357			else
358			{
359				do
360				{
361					back(1, position(TOP), 1, 0);
362					pos = position(BOTTOM_PLUS_ONE);
363				} while (pos == NULL_POSITION);
364			}
365		} else
366		{
367			eof_bell();
368			hit_eof++;
369			return;
370		}
371	}
372	forw(n, pos, force, only_last, 0);
373}
374
375/*
376 * Display n more lines, backward.
377 * Start just before the line currently displayed at the top of the screen.
378 */
379	public void
380backward(n, force, only_last)
381	int n;
382	int force;
383	int only_last;
384{
385	POSITION pos;
386
387	pos = position(TOP);
388	if (pos == NULL_POSITION && (!force || position(BOTTOM) == 0))
389	{
390		eof_bell();
391		return;
392	}
393	back(n, pos, force, only_last);
394}
395
396/*
397 * Get the backwards scroll limit.
398 * Must call this function instead of just using the value of
399 * back_scroll, because the default case depends on sc_height and
400 * top_scroll, as well as back_scroll.
401 */
402	public int
403get_back_scroll()
404{
405	if (no_back_scroll)
406		return (0);
407	if (back_scroll >= 0)
408		return (back_scroll);
409	if (top_scroll)
410		return (sc_height - 2);
411	return (10000); /* infinity */
412}
413