2 * Copyright (C) 1984-2011 Mark Nudelman
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.
7 * For more information about less, or for information on how to
8 * contact the author, see the README file.
13 * Primitives for displaying the file on the screen,
14 * scrolling either forward or backward.
20 public int screen_trashed;
22 public int no_back_scroll = 0;
23 public int forw_prompt;
26 extern int top_scroll;
28 extern int sc_width, sc_height;
29 extern int plusoption;
30 extern int forw_scroll;
31 extern int back_scroll;
32 extern int ignore_eoi;
34 extern int final_attr;
37 extern char *tagoption;
41 * Sound the bell to indicate user is trying to move past end of file.
46 if (quiet == NOT_QUIET)
53 * Check to see if the end of file is currently displayed.
63 if (ch_length() == NULL_POSITION)
65 * If the file length is not known,
66 * we can't possibly be displaying EOF.
71 * If the bottom line is empty, we are at EOF.
72 * If the bottom line ends at the file length,
73 * we must be just at EOF.
75 pos = position(BOTTOM_PLUS_ONE);
76 return (pos == NULL_POSITION || pos == ch_length());
80 * Check to see if the entire file is currently displayed.
83 entire_file_displayed()
87 /* Make sure last line of file is displayed. */
91 /* Make sure first line of file is displayed. */
93 return (pos == NULL_POSITION || pos == 0);
97 * If the screen is "squished", repaint it.
98 * "Squished" means the first displayed line is not at the top
99 * of the screen; this can happen when we display a short file
100 * for the first time.
112 * Display n lines, scrolling forward,
113 * starting at position pos in the input file.
114 * "force" means display the n lines even if we hit end of file.
115 * "only_last" means display only the last screenful if n > screen size.
116 * "nblank" is the number of blank lines to draw before the first
117 * real line. If nblank > 0, the pos must be NULL_POSITION.
118 * The first real line after the blanks will start at ch_zero().
121 forw(n, pos, force, only_last, nblank)
131 static int first_time = 1;
136 * do_repaint tells us not to display anything till the end,
137 * then just repaint the entire screen.
138 * We repaint if we are supposed to display only the last
139 * screenful and the request is for more than a screenful.
140 * Also if the request exceeds the forward scroll limit
141 * (but not if the request is for exactly a screenful, since
142 * repainting itself involves scrolling forward a screenful).
144 do_repaint = (only_last && n > sc_height-1) ||
145 (forw_scroll >= 0 && n > forw_scroll && n != sc_height-1);
149 if (top_scroll && n >= sc_height - 1 && pos != ch_length())
152 * Start a new screen.
153 * {{ This is not really desirable if we happen
154 * to hit eof in the middle of this screen,
155 * but we don't yet know if that will happen. }}
164 if (pos != position(BOTTOM_PLUS_ONE) || empty_screen())
167 * This is not contiguous with what is
168 * currently displayed. Clear the screen image
169 * (position table) and start a new screen.
178 } else if (!first_time)
180 putstr("...skipping...\n");
188 * Read the next line of input.
193 * Still drawing blanks; don't get a line
195 * If this is the last blank line, get ready to
196 * read a line starting at ch_zero() next time.
203 * Get the next line from the file.
205 pos = forw_line(pos);
206 if (pos == NULL_POSITION)
209 * End of file: stop here unless the top line
210 * is still empty, or "force" is true.
211 * Even if force is true, stop when the last
212 * line in the file reaches the top of screen.
215 if (!force && position(TOP) != NULL_POSITION)
217 if (!empty_lines(0, 0) &&
218 !empty_lines(1, 1) &&
219 empty_lines(2, sc_height-1))
224 * Add the position of the next line to the position table.
225 * Display the current line on the screen.
232 * If this is the first screen displayed and
233 * we hit an early EOF (i.e. before the requested
234 * number of lines), we "squish" the display down
235 * at the bottom of the screen.
236 * But don't do this if a + option or a -t option
237 * was given. These options can cause us to
238 * start the display after the beginning of the file,
239 * and it is not appropriate to squish in that case.
241 if (first_time && pos == NULL_POSITION && !top_scroll &&
253 * Can't call clear_eol here. The cursor might be at end of line
254 * on an ignaw terminal, so clear_eol would clear the last char
255 * of the current line instead of all of the next line.
256 * If we really need to do this on clear_bg terminals, we need
257 * to find a better way.
260 if (clear_bg && apply_at_specials(final_attr) != AT_NORMAL)
263 * Writing the last character on the last line
264 * of the display may have scrolled the screen.
265 * If we were in standout mode, clear_bg terminals
266 * will fill the new line with the standout color.
267 * Now we're in normal mode again, so clear the line.
280 (void) currline(BOTTOM);
284 * Display n lines, scrolling backward.
287 back(n, pos, force, only_last)
297 do_repaint = (n > get_back_scroll() || (only_last && n > sc_height-1));
301 * Get the previous line of input.
303 pos = back_line(pos);
304 if (pos == NULL_POSITION)
307 * Beginning of file: stop here unless "force" is true.
313 * Add the position of the previous line to the position table.
314 * Display the line on the screen.
332 (void) currline(BOTTOM);
336 * Display n more lines, forward.
337 * Start just after the line currently displayed at the bottom of the screen.
340 forward(n, force, only_last)
347 if (get_quit_at_eof() && eof_displayed() && !(ch_getflags() & CH_HELPFILE))
350 * If the -e flag is set and we're trying to go
351 * forward from end-of-file, go on to the next file.
358 pos = position(BOTTOM_PLUS_ONE);
359 if (pos == NULL_POSITION && (!force || empty_lines(2, sc_height-1)))
364 * ignore_eoi is to support A_F_FOREVER.
365 * Back up until there is a line at the bottom
374 back(1, position(TOP), 1, 0);
375 pos = position(BOTTOM_PLUS_ONE);
376 } while (pos == NULL_POSITION);
384 forw(n, pos, force, only_last, 0);
388 * Display n more lines, backward.
389 * Start just before the line currently displayed at the top of the screen.
392 backward(n, force, only_last)
400 if (pos == NULL_POSITION && (!force || position(BOTTOM) == 0))
405 back(n, pos, force, only_last);
409 * Get the backwards scroll limit.
410 * Must call this function instead of just using the value of
411 * back_scroll, because the default case depends on sc_height and
412 * top_scroll, as well as back_scroll.
419 if (back_scroll >= 0)
420 return (back_scroll);
422 return (sc_height - 2);
423 return (10000); /* infinity */