forwback.c revision 60786 
1/*
2 * Copyright (C) 1984-2000  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;
24
25extern int sigs;
26extern int top_scroll;
27extern int quiet;
28extern int sc_width, sc_height;
29extern int quit_at_eof;
30extern int plusoption;
31extern int forw_scroll;
32extern int back_scroll;
33extern int ignore_eoi;
34extern int clear_bg;
35extern int final_attr;
36#if TAGS
37extern char *tagoption;
38#endif
39
40/*
41 * Sound the bell to indicate user is trying to move past end of file.
42 */
43	static void
44eof_bell()
45{
46	if (quiet == NOT_QUIET)
47		bell();
48	else
49		vbell();
50}
51
52/*
53 * Check to see if the end of file is currently "displayed".
54 */
55	static void
56eof_check()
57{
58	POSITION pos;
59
60	if (ignore_eoi)
61		return;
62	if (ABORT_SIGS())
63		return;
64	/*
65	 * If the bottom line is empty, we are at EOF.
66	 * If the bottom line ends at the file length,
67	 * we must be just at EOF.
68	 */
69	pos = position(BOTTOM_PLUS_ONE);
70	if (pos == NULL_POSITION || pos == ch_length())
71		hit_eof++;
72}
73
74/*
75 * If the screen is "squished", repaint it.
76 * "Squished" means the first displayed line is not at the top
77 * of the screen; this can happen when we display a short file
78 * for the first time.
79 */
80	static void
81squish_check()
82{
83	if (!squished)
84		return;
85	squished = 0;
86	repaint();
87}
88
89/*
90 * Display n lines, scrolling forward,
91 * starting at position pos in the input file.
92 * "force" means display the n lines even if we hit end of file.
93 * "only_last" means display only the last screenful if n > screen size.
94 * "nblank" is the number of blank lines to draw before the first
95 *   real line.  If nblank > 0, the pos must be NULL_POSITION.
96 *   The first real line after the blanks will start at ch_zero().
97 */
98	public void
99forw(n, pos, force, only_last, nblank)
100	register int n;
101	POSITION pos;
102	int force;
103	int only_last;
104	int nblank;
105{
106	int eof = 0;
107	int nlines = 0;
108	int do_repaint;
109	static int first_time = 1;
110
111	squish_check();
112
113	/*
114	 * do_repaint tells us not to display anything till the end,
115	 * then just repaint the entire screen.
116	 * We repaint if we are supposed to display only the last
117	 * screenful and the request is for more than a screenful.
118	 * Also if the request exceeds the forward scroll limit
119	 * (but not if the request is for exactly a screenful, since
120	 * repainting itself involves scrolling forward a screenful).
121	 */
122	do_repaint = (only_last && n > sc_height-1) ||
123		(forw_scroll >= 0 && n > forw_scroll && n != sc_height-1);
124
125	if (!do_repaint)
126	{
127		/*
128		 * Forget any current line shift we might have
129		 * (from the last line of the previous screenful).
130		 */
131		extern int cshift;
132		cshift = 0;
133
134		if (top_scroll && n >= sc_height - 1 && pos != ch_length())
135		{
136			/*
137			 * Start a new screen.
138			 * {{ This is not really desirable if we happen
139			 *    to hit eof in the middle of this screen,
140			 *    but we don't yet know if that will happen. }}
141			 */
142			pos_clear();
143			add_forw_pos(pos);
144			force = 1;
145			if (top_scroll == OPT_ONPLUS || first_time)
146				clear();
147			home();
148		} else
149		{
150			clear_bot();
151		}
152
153		if (pos != position(BOTTOM_PLUS_ONE) || empty_screen())
154		{
155			/*
156			 * This is not contiguous with what is
157			 * currently displayed.  Clear the screen image
158			 * (position table) and start a new screen.
159			 */
160			pos_clear();
161			add_forw_pos(pos);
162			force = 1;
163			if (top_scroll)
164			{
165				if (top_scroll == OPT_ONPLUS)
166					clear();
167				home();
168			} else if (!first_time)
169			{
170				putstr("...skipping...\n");
171			}
172		}
173	}
174
175	while (--n >= 0)
176	{
177		/*
178		 * Read the next line of input.
179		 */
180		if (nblank > 0)
181		{
182			/*
183			 * Still drawing blanks; don't get a line
184			 * from the file yet.
185			 * If this is the last blank line, get ready to
186			 * read a line starting at ch_zero() next time.
187			 */
188			if (--nblank == 0)
189				pos = ch_zero();
190		} else
191		{
192			/*
193			 * Get the next line from the file.
194			 */
195			pos = forw_line(pos);
196			if (pos == NULL_POSITION)
197			{
198				/*
199				 * End of file: stop here unless the top line
200				 * is still empty, or "force" is true.
201				 * Even if force is true, stop when the last
202				 * line in the file reaches the top of screen.
203				 */
204				eof = 1;
205				if (!force && position(TOP) != NULL_POSITION)
206					break;
207				if (!empty_lines(0, 0) &&
208				    !empty_lines(1, 1) &&
209				     empty_lines(2, sc_height-1))
210					break;
211			}
212		}
213		/*
214		 * Add the position of the next line to the position table.
215		 * Display the current line on the screen.
216		 */
217		add_forw_pos(pos);
218		nlines++;
219		if (do_repaint)
220			continue;
221		/*
222		 * If this is the first screen displayed and
223		 * we hit an early EOF (i.e. before the requested
224		 * number of lines), we "squish" the display down
225		 * at the bottom of the screen.
226		 * But don't do this if a + option or a -t option
227		 * was given.  These options can cause us to
228		 * start the display after the beginning of the file,
229		 * and it is not appropriate to squish in that case.
230		 */
231		if (first_time && pos == NULL_POSITION && !top_scroll &&
232#if TAGS
233		    tagoption == NULL &&
234#endif
235		    !plusoption)
236		{
237			squished = 1;
238			continue;
239		}
240		if (top_scroll == OPT_ON)
241			clear_eol();
242		put_line();
243		if (clear_bg && final_attr != AT_NORMAL)
244		{
245			/*
246			 * Writing the last character on the last line
247			 * of the display may have scrolled the screen.
248			 * If we were in standout mode, clear_bg terminals
249			 * will fill the new line with the standout color.
250			 * Now we're in normal mode again, so clear the line.
251			 */
252			clear_eol();
253		}
254	}
255
256	if (ignore_eoi)
257		hit_eof = 0;
258	else if (eof && !ABORT_SIGS())
259		hit_eof++;
260	else
261		eof_check();
262	if (nlines == 0)
263		eof_bell();
264	else if (do_repaint)
265		repaint();
266	first_time = 0;
267	(void) currline(BOTTOM);
268}
269
270/*
271 * Display n lines, scrolling backward.
272 */
273	public void
274back(n, pos, force, only_last)
275	register int n;
276	POSITION pos;
277	int force;
278	int only_last;
279{
280	int nlines = 0;
281	int do_repaint;
282
283	squish_check();
284	do_repaint = (n > get_back_scroll() || (only_last && n > sc_height-1));
285	hit_eof = 0;
286	while (--n >= 0)
287	{
288		/*
289		 * Get the previous line of input.
290		 */
291		pos = back_line(pos);
292		if (pos == NULL_POSITION)
293		{
294			/*
295			 * Beginning of file: stop here unless "force" is true.
296			 */
297			if (!force)
298				break;
299		}
300		/*
301		 * Add the position of the previous line to the position table.
302		 * Display the line on the screen.
303		 */
304		add_back_pos(pos);
305		nlines++;
306		if (!do_repaint)
307		{
308			home();
309			add_line();
310			put_line();
311		}
312	}
313
314	eof_check();
315	if (nlines == 0)
316		eof_bell();
317	else if (do_repaint)
318		repaint();
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 (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