contrib/less/forwback.c

   1 /*
   2  * Copyright (C) 1984-2011  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
  20 public int screen_trashed;
  21 public int squished;
  22 public int no_back_scroll = 0;
  23 public int forw_prompt;
  24
  25 extern int sigs;
  26 extern int top_scroll;
  27 extern int quiet;
  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;
  33 extern int clear_bg;
  34 extern int final_attr;
  35 extern int oldbot;
  36 #if TAGS
  37 extern 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
  44 eof_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         public int
  56 eof_displayed()
  57 {
  58         POSITION pos;
  59
  60         if (ignore_eoi)
  61                 return (0);
  62
  63         if (ch_length() == NULL_POSITION)
  64                 /*
  65                  * If the file length is not known,
  66                  * we can't possibly be displaying EOF.
  67                  */
  68                 return (0);
  69
  70         /*
  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.
  74          */
  75         pos = position(BOTTOM_PLUS_ONE);
  76         return (pos == NULL_POSITION || pos == ch_length());
  77 }
  78
  79 /*
  80  * Check to see if the entire file is currently displayed.
  81  */
  82         public int
  83 entire_file_displayed()
  84 {
  85         POSITION pos;
  86
  87         /* Make sure last line of file is displayed. */
  88         if (!eof_displayed())
  89                 return (0);
  90
  91         /* Make sure first line of file is displayed. */
  92         pos = position(0);
  93         return (pos == NULL_POSITION || pos == 0);
  94 }
  95
  96 /*
  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.
 101  */
 102         public void
 103 squish_check()
 104 {
 105         if (!squished)
 106                 return;
 107         squished = 0;
 108         repaint();
 109 }
 110
 111 /*
 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().
 119  */
 120         public void
 121 forw(n, pos, force, only_last, nblank)
 122         register int n;
 123         POSITION pos;
 124         int force;
 125         int only_last;
 126         int nblank;
 127 {
 128         int eof = 0;
 129         int nlines = 0;
 130         int do_repaint;
 131         static int first_time = 1;
 132
 133         squish_check();
 134
 135         /*
 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).
 143          */
 144         do_repaint = (only_last && n > sc_height-1) ||
 145                 (forw_scroll >= 0 && n > forw_scroll && n != sc_height-1);
 146
 147         if (!do_repaint)
 148         {
 149                 if (top_scroll && n >= sc_height - 1 && pos != ch_length())
 150                 {
 151                         /*
 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. }}
 156                          */
 157                         pos_clear();
 158                         add_forw_pos(pos);
 159                         force = 1;
 160                         clear();
 161                         home();
 162                 }
 163
 164                 if (pos != position(BOTTOM_PLUS_ONE) || empty_screen())
 165                 {
 166                         /*
 167                          * This is not contiguous with what is
 168                          * currently displayed.  Clear the screen image
 169                          * (position table) and start a new screen.
 170                          */
 171                         pos_clear();
 172                         add_forw_pos(pos);
 173                         force = 1;
 174                         if (top_scroll)
 175                         {
 176                                 clear();
 177                                 home();
 178                         } else if (!first_time)
 179                         {
 180                                 putstr("...skipping...\n");
 181                         }
 182                 }
 183         }
 184
 185         while (--n >= 0)
 186         {
 187                 /*
 188                  * Read the next line of input.
 189                  */
 190                 if (nblank > 0)
 191                 {
 192                         /*
 193                          * Still drawing blanks; don't get a line
 194                          * from the file yet.
 195                          * If this is the last blank line, get ready to
 196                          * read a line starting at ch_zero() next time.
 197                          */
 198                         if (--nblank == 0)
 199                                 pos = ch_zero();
 200                 } else
 201                 {
 202                         /*
 203                          * Get the next line from the file.
 204                          */
 205                         pos = forw_line(pos);
 206                         if (pos == NULL_POSITION)
 207                         {
 208                                 /*
 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.
 213                                  */
 214                                 eof = 1;
 215                                 if (!force && position(TOP) != NULL_POSITION)
 216                                         break;
 217                                 if (!empty_lines(0, 0) &&
 218                                     !empty_lines(1, 1) &&
 219                                      empty_lines(2, sc_height-1))
 220                                         break;
 221                         }
 222                 }
 223                 /*
 224                  * Add the position of the next line to the position table.
 225                  * Display the current line on the screen.
 226                  */
 227                 add_forw_pos(pos);
 228                 nlines++;
 229                 if (do_repaint)
 230                         continue;
 231                 /*
 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.
 240                  */
 241                 if (first_time && pos == NULL_POSITION && !top_scroll &&
 242 #if TAGS
 243                     tagoption == NULL &&
 244 #endif
 245                     !plusoption)
 246                 {
 247                         squished = 1;
 248                         continue;
 249                 }
 250                 put_line();
 251 #if 0
 252                 /* {{
 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.
 258                  * }}
 259                  */
 260                 if (clear_bg && apply_at_specials(final_attr) != AT_NORMAL)
 261                 {
 262                         /*
 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.
 268                          */
 269                         clear_eol();
 270                 }
 271 #endif
 272                 forw_prompt = 1;
 273         }
 274
 275         if (nlines == 0)
 276                 eof_bell();
 277         else if (do_repaint)
 278                 repaint();
 279         first_time = 0;
 280         (void) currline(BOTTOM);
 281 }
 282
 283 /*
 284  * Display n lines, scrolling backward.
 285  */
 286         public void
 287 back(n, pos, force, only_last)
 288         register int n;
 289         POSITION pos;
 290         int force;
 291         int only_last;
 292 {
 293         int nlines = 0;
 294         int do_repaint;
 295
 296         squish_check();
 297         do_repaint = (n > get_back_scroll() || (only_last && n > sc_height-1));
 298         while (--n >= 0)
 299         {
 300                 /*
 301                  * Get the previous line of input.
 302                  */
 303                 pos = back_line(pos);
 304                 if (pos == NULL_POSITION)
 305                 {
 306                         /*
 307                          * Beginning of file: stop here unless "force" is true.
 308                          */
 309                         if (!force)
 310                                 break;
 311                 }
 312                 /*
 313                  * Add the position of the previous line to the position table.
 314                  * Display the line on the screen.
 315                  */
 316                 add_back_pos(pos);
 317                 nlines++;
 318                 if (!do_repaint)
 319                 {
 320                         home();
 321                         add_line();
 322                         put_line();
 323                 }
 324         }
 325
 326         if (nlines == 0)
 327                 eof_bell();
 328         else if (do_repaint)
 329                 repaint();
 330         else if (!oldbot)
 331                 lower_left();
 332         (void) currline(BOTTOM);
 333 }
 334
 335 /*
 336  * Display n more lines, forward.
 337  * Start just after the line currently displayed at the bottom of the screen.
 338  */
 339         public void
 340 forward(n, force, only_last)
 341         int n;
 342         int force;
 343         int only_last;
 344 {
 345         POSITION pos;
 346
 347         if (get_quit_at_eof() && eof_displayed() && !(ch_getflags() & CH_HELPFILE))
 348         {
 349                 /*
 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.
 352                  */
 353                 if (edit_next(1))
 354                         quit(QUIT_OK);
 355                 return;
 356         }
 357
 358         pos = position(BOTTOM_PLUS_ONE);
 359         if (pos == NULL_POSITION && (!force || empty_lines(2, sc_height-1)))
 360         {
 361                 if (ignore_eoi)
 362                 {
 363                         /*
 364                          * ignore_eoi is to support A_F_FOREVER.
 365                          * Back up until there is a line at the bottom
 366                          * of the screen.
 367                          */
 368                         if (empty_screen())
 369                                 pos = ch_zero();
 370                         else
 371                         {
 372                                 do
 373                                 {
 374                                         back(1, position(TOP), 1, 0);
 375                                         pos = position(BOTTOM_PLUS_ONE);
 376                                 } while (pos == NULL_POSITION);
 377                         }
 378                 } else
 379                 {
 380                         eof_bell();
 381                         return;
 382                 }
 383         }
 384         forw(n, pos, force, only_last, 0);
 385 }
 386
 387 /*
 388  * Display n more lines, backward.
 389  * Start just before the line currently displayed at the top of the screen.
 390  */
 391         public void
 392 backward(n, force, only_last)
 393         int n;
 394         int force;
 395         int only_last;
 396 {
 397         POSITION pos;
 398
 399         pos = position(TOP);
 400         if (pos == NULL_POSITION && (!force || position(BOTTOM) == 0))
 401         {
 402                 eof_bell();
 403                 return;
 404         }
 405         back(n, pos, force, only_last);
 406 }
 407
 408 /*
 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.
 413  */
 414         public int
 415 get_back_scroll()
 416 {
 417         if (no_back_scroll)
 418                 return (0);
 419         if (back_scroll >= 0)
 420                 return (back_scroll);
 421         if (top_scroll)
 422                 return (sc_height - 2);
 423         return (10000); /* infinity */
 424 }