contrib/less-4/forwback.c

   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
  20 public int hit_eof;     /* Keeps track of how many times we hit end of file */
  21 public int screen_trashed;
  22 public int squished;
  23 public int no_back_scroll = 0;
  24 public int forw_prompt;
  25
  26 extern int sigs;
  27 extern int top_scroll;
  28 extern int quiet;
  29 extern int sc_width, sc_height;
  30 extern int plusoption;
  31 extern int forw_scroll;
  32 extern int back_scroll;
  33 extern int ignore_eoi;
  34 extern int clear_bg;
  35 extern int final_attr;
  36 extern int oldbot;
  37 #if TAGS
  38 extern 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
  45 eof_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
  57 eof_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
  82 squish_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
 100 forw(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
 272 back(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
 327 forward(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
 380 backward(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
 403 get_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 }