1/*
2 * Copyright (C) 1984-2023  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 * Primitives for displaying the file on the screen,
13 * scrolling either forward or backward.
14 */
15
16#include "less.h"
17#include "position.h"
18
19extern int less_is_more;
20
21public int screen_trashed;
22public int squished;
23public int no_back_scroll = 0;
24public int forw_prompt;
25public int first_time = 1;
26
27extern int sigs;
28extern int top_scroll;
29extern int quiet;
30extern int sc_width, sc_height;
31extern int hshift;
32extern int auto_wrap;
33extern int plusoption;
34extern int forw_scroll;
35extern int back_scroll;
36extern int ignore_eoi;
37extern int clear_bg;
38extern int final_attr;
39extern int header_lines;
40extern int header_cols;
41extern int full_screen;
42#if HILITE_SEARCH
43extern int size_linebuf;
44extern int hilite_search;
45extern int status_col;
46#endif
47#if TAGS
48extern char *tagoption;
49#endif
50
51/*
52 * Sound the bell to indicate user is trying to move past end of file.
53 */
54public void eof_bell(void)
55{
56#if HAVE_TIME
57	static time_type last_eof_bell = 0;
58	time_type now = get_time();
59	if (now == last_eof_bell) /* max once per second */
60		return;
61	last_eof_bell = now;
62#endif
63	if (quiet == NOT_QUIET)
64		bell();
65	else
66		vbell();
67}
68
69/*
70 * Check to see if the end of file is currently displayed.
71 */
72public int eof_displayed(void)
73{
74	POSITION pos;
75
76	if (ignore_eoi)
77		return (0);
78
79	if (ch_length() == NULL_POSITION)
80		/*
81		 * If the file length is not known,
82		 * we can't possibly be displaying EOF.
83		 */
84		return (0);
85
86	/*
87	 * If the bottom line is empty, we are at EOF.
88	 * If the bottom line ends at the file length,
89	 * we must be just at EOF.
90	 */
91	pos = position(BOTTOM_PLUS_ONE);
92	return (pos == NULL_POSITION || pos == ch_length());
93}
94
95/*
96 * Check to see if the entire file is currently displayed.
97 */
98public int entire_file_displayed(void)
99{
100	POSITION pos;
101
102	/* Make sure last line of file is displayed. */
103	if (!eof_displayed())
104		return (0);
105
106	/* Make sure first line of file is displayed. */
107	pos = position(0);
108	return (pos == NULL_POSITION || pos == 0);
109}
110
111/*
112 * If the screen is "squished", repaint it.
113 * "Squished" means the first displayed line is not at the top
114 * of the screen; this can happen when we display a short file
115 * for the first time.
116 */
117public void squish_check(void)
118{
119	if (!squished)
120		return;
121	squished = 0;
122	repaint();
123}
124
125/*
126 * Read the first pfx columns of the next line.
127 * If skipeol==0 stop there, otherwise read and discard chars to end of line.
128 */
129static POSITION forw_line_pfx(POSITION pos, int pfx, int skipeol)
130{
131	int save_sc_width = sc_width;
132	int save_auto_wrap = auto_wrap;
133	int save_hshift = hshift;
134	/* Set fake sc_width to force only pfx chars to be read. */
135	sc_width = pfx + line_pfx_width();
136	auto_wrap = 0;
137	hshift = 0;
138	pos = forw_line_seg(pos, skipeol, FALSE, FALSE);
139	sc_width = save_sc_width;
140	auto_wrap = save_auto_wrap;
141	hshift = save_hshift;
142	return pos;
143}
144
145/*
146 * Set header text color.
147 * Underline last line of headers, but not at beginning of file
148 * (where there is no gap between the last header line and the next line).
149 */
150static void set_attr_header(int ln)
151{
152	set_attr_line(AT_COLOR_HEADER);
153	if (ln+1 == header_lines && position(0) != ch_zero())
154		set_attr_line(AT_UNDERLINE);
155}
156
157/*
158 * Display file headers, overlaying text already drawn
159 * at top and left of screen.
160 */
161public int overlay_header(void)
162{
163	POSITION pos = ch_zero(); /* header lines are at beginning of file */
164	int ln;
165	int moved = FALSE;
166
167	if (header_lines > 0)
168	{
169		/* Draw header_lines lines from start of file at top of screen. */
170		home();
171		for (ln = 0; ln < header_lines; ++ln)
172		{
173			pos = forw_line(pos);
174			set_attr_header(ln);
175			clear_eol();
176			put_line();
177		}
178		moved = TRUE;
179	}
180	if (header_cols > 0)
181	{
182		/* Draw header_cols columns at left of each line. */
183		home();
184		pos = ch_zero();
185		for (ln = 0; ln < sc_height-1; ++ln)
186		{
187			if (ln >= header_lines) /* switch from header lines to normal lines */
188				pos = position(ln);
189			if (pos == NULL_POSITION)
190				putchr('\n');
191			else
192			{
193				/* Need skipeol for all header lines except the last one. */
194				pos = forw_line_pfx(pos, header_cols, ln+1 < header_lines);
195				set_attr_header(ln);
196				put_line();
197			}
198		}
199		moved = TRUE;
200	}
201	if (moved)
202		lower_left();
203	return moved;
204}
205
206/*
207 * Display n lines, scrolling forward,
208 * starting at position pos in the input file.
209 * "force" means display the n lines even if we hit end of file.
210 * "only_last" means display only the last screenful if n > screen size.
211 * "nblank" is the number of blank lines to draw before the first
212 *   real line.  If nblank > 0, the pos must be NULL_POSITION.
213 *   The first real line after the blanks will start at ch_zero().
214 */
215public void forw(int n, POSITION pos, int force, int only_last, int nblank)
216{
217	int nlines = 0;
218	int do_repaint;
219
220	squish_check();
221
222	/*
223	 * do_repaint tells us not to display anything till the end,
224	 * then just repaint the entire screen.
225	 * We repaint if we are supposed to display only the last
226	 * screenful and the request is for more than a screenful.
227	 * Also if the request exceeds the forward scroll limit
228	 * (but not if the request is for exactly a screenful, since
229	 * repainting itself involves scrolling forward a screenful).
230	 */
231	do_repaint = (only_last && n > sc_height-1) ||
232		(forw_scroll >= 0 && n > forw_scroll && n != sc_height-1);
233
234#if HILITE_SEARCH
235	if (pos != NULL_POSITION && (hilite_search == OPT_ONPLUS || is_filtering() || status_col)) {
236		prep_hilite(pos, pos + 4*size_linebuf, ignore_eoi ? 1 : -1);
237		pos = next_unfiltered(pos);
238	}
239#endif
240
241	if (!do_repaint)
242	{
243		if (top_scroll && n >= sc_height - 1 && pos != ch_length())
244		{
245			/*
246			 * Start a new screen.
247			 * {{ This is not really desirable if we happen
248			 *    to hit eof in the middle of this screen,
249			 *    but we don't yet know if that will happen. }}
250			 */
251			pos_clear();
252			add_forw_pos(pos);
253			force = 1;
254			if (less_is_more == 0) {
255				clear();
256				home();
257			}
258		}
259
260		if (pos != position(BOTTOM_PLUS_ONE) || empty_screen())
261		{
262			/*
263			 * This is not contiguous with what is
264			 * currently displayed.  Clear the screen image
265			 * (position table) and start a new screen.
266			 */
267			pos_clear();
268			add_forw_pos(pos);
269			force = 1;
270			if (top_scroll)
271			{
272				clear();
273				home();
274			} else if (!first_time && !is_filtering() && full_screen)
275			{
276				putstr("...skipping...\n");
277			}
278		}
279	}
280
281	while (--n >= 0)
282	{
283		/*
284		 * Read the next line of input.
285		 */
286		if (nblank > 0)
287		{
288			/*
289			 * Still drawing blanks; don't get a line
290			 * from the file yet.
291			 * If this is the last blank line, get ready to
292			 * read a line starting at ch_zero() next time.
293			 */
294			if (--nblank == 0)
295				pos = ch_zero();
296		} else
297		{
298			/*
299			 * Get the next line from the file.
300			 */
301			pos = forw_line(pos);
302#if HILITE_SEARCH
303			pos = next_unfiltered(pos);
304#endif
305			if (pos == NULL_POSITION)
306			{
307				/*
308				 * End of file: stop here unless the top line
309				 * is still empty, or "force" is true.
310				 * Even if force is true, stop when the last
311				 * line in the file reaches the top of screen.
312				 */
313				if (!force && position(TOP) != NULL_POSITION)
314					break;
315				if (!empty_lines(0, 0) &&
316				    !empty_lines(1, 1) &&
317				     empty_lines(2, sc_height-1))
318					break;
319			}
320		}
321		/*
322		 * Add the position of the next line to the position table.
323		 * Display the current line on the screen.
324		 */
325		add_forw_pos(pos);
326		nlines++;
327		if (do_repaint)
328			continue;
329		/*
330		 * If this is the first screen displayed and
331		 * we hit an early EOF (i.e. before the requested
332		 * number of lines), we "squish" the display down
333		 * at the bottom of the screen.
334		 * But don't do this if a + option or a -t option
335		 * was given.  These options can cause us to
336		 * start the display after the beginning of the file,
337		 * and it is not appropriate to squish in that case.
338		 */
339		if ((first_time || less_is_more) &&
340		    pos == NULL_POSITION && !top_scroll &&
341		    header_lines == 0 && header_cols == 0 &&
342#if TAGS
343		    tagoption == NULL &&
344#endif
345		    !plusoption)
346		{
347			squished = 1;
348			continue;
349		}
350		put_line();
351#if 0
352		/* {{
353		 * Can't call clear_eol here.  The cursor might be at end of line
354		 * on an ignaw terminal, so clear_eol would clear the last char
355		 * of the current line instead of all of the next line.
356		 * If we really need to do this on clear_bg terminals, we need
357		 * to find a better way.
358		 * }}
359		 */
360		if (clear_bg && apply_at_specials(final_attr) != AT_NORMAL)
361		{
362			/*
363			 * Writing the last character on the last line
364			 * of the display may have scrolled the screen.
365			 * If we were in standout mode, clear_bg terminals
366			 * will fill the new line with the standout color.
367			 * Now we're in normal mode again, so clear the line.
368			 */
369			clear_eol();
370		}
371#endif
372		forw_prompt = 1;
373	}
374
375	if (header_lines > 0)
376	{
377		/*
378		 * Don't allow ch_zero to appear on screen except at top of screen.
379		 * Otherwise duplicate header lines may be displayed.
380		 */
381		if (onscreen(ch_zero()) > 0)
382		{
383			jump_loc(ch_zero(), 0); /* {{ yuck }} */
384			return;
385		}
386	}
387	if (nlines == 0 && !ignore_eoi)
388		eof_bell();
389	else if (do_repaint)
390		repaint();
391	else
392	{
393		overlay_header();
394		/* lower_left(); {{ considered harmful? }} */
395	}
396	first_time = 0;
397	(void) currline(BOTTOM);
398}
399
400/*
401 * Display n lines, scrolling backward.
402 */
403public void back(int n, POSITION pos, int force, int only_last)
404{
405	int nlines = 0;
406	int do_repaint;
407
408	squish_check();
409	do_repaint = (n > get_back_scroll() || (only_last && n > sc_height-1) || header_lines > 0);
410#if HILITE_SEARCH
411	if (pos != NULL_POSITION && (hilite_search == OPT_ONPLUS || is_filtering() || status_col)) {
412		prep_hilite((pos < 3*size_linebuf) ? 0 : pos - 3*size_linebuf, pos, -1);
413	}
414#endif
415	while (--n >= 0)
416	{
417		/*
418		 * Get the previous line of input.
419		 */
420#if HILITE_SEARCH
421		pos = prev_unfiltered(pos);
422#endif
423
424		pos = back_line(pos);
425		if (pos == NULL_POSITION)
426		{
427			/*
428			 * Beginning of file: stop here unless "force" is true.
429			 */
430			if (!force)
431				break;
432		}
433		/*
434		 * Add the position of the previous line to the position table.
435		 * Display the line on the screen.
436		 */
437		add_back_pos(pos);
438		nlines++;
439		if (!do_repaint)
440		{
441			home();
442			add_line();
443			put_line();
444		}
445	}
446	if (nlines == 0)
447		eof_bell();
448	else if (do_repaint)
449		repaint();
450	else
451	{
452		overlay_header();
453		lower_left();
454	}
455	(void) currline(BOTTOM);
456}
457
458/*
459 * Display n more lines, forward.
460 * Start just after the line currently displayed at the bottom of the screen.
461 */
462public void forward(int n, int force, int only_last)
463{
464	POSITION pos;
465
466	if (get_quit_at_eof() && eof_displayed() && !(ch_getflags() & CH_HELPFILE))
467	{
468		/*
469		 * If the -e flag is set and we're trying to go
470		 * forward from end-of-file, go on to the next file.
471		 */
472		if (edit_next(1))
473			quit(QUIT_OK);
474		return;
475	}
476
477	pos = position(BOTTOM_PLUS_ONE);
478	if (pos == NULL_POSITION && (!force || empty_lines(2, sc_height-1)))
479	{
480		if (ignore_eoi)
481		{
482			/*
483			 * ignore_eoi is to support A_F_FOREVER.
484			 * Back up until there is a line at the bottom
485			 * of the screen.
486			 */
487			if (empty_screen())
488				pos = ch_zero();
489			else
490			{
491				do
492				{
493					back(1, position(TOP), 1, 0);
494					pos = position(BOTTOM_PLUS_ONE);
495				} while (pos == NULL_POSITION && !ABORT_SIGS());
496			}
497		} else
498		{
499			eof_bell();
500			return;
501		}
502	}
503	forw(n, pos, force, only_last, 0);
504}
505
506/*
507 * Display n more lines, backward.
508 * Start just before the line currently displayed at the top of the screen.
509 */
510public void backward(int n, int force, int only_last)
511{
512	POSITION pos;
513
514	pos = position(TOP);
515	if (pos == NULL_POSITION && (!force || position(BOTTOM) == 0))
516	{
517		eof_bell();
518		return;
519	}
520	back(n, pos, force, only_last);
521}
522
523/*
524 * Get the backwards scroll limit.
525 * Must call this function instead of just using the value of
526 * back_scroll, because the default case depends on sc_height and
527 * top_scroll, as well as back_scroll.
528 */
529public int get_back_scroll(void)
530{
531	if (no_back_scroll)
532		return (0);
533	if (back_scroll >= 0)
534		return (back_scroll);
535	if (top_scroll)
536		return (sc_height - 2);
537	return (10000); /* infinity */
538}
539
540/*
541 * Will the entire file fit on one screen?
542 */
543public int get_one_screen(void)
544{
545	int nlines;
546	POSITION pos = ch_zero();
547
548	for (nlines = 0;  nlines < sc_height;  nlines++)
549	{
550		pos = forw_line(pos);
551		if (pos == NULL_POSITION) break;
552	}
553	return (nlines < sc_height);
554}
555