contrib/less-381/forwback.c

   1 /*
   2  * Copyright (C) 1984-2002  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
  25 extern int sigs;
  26 extern int top_scroll;
  27 extern int quiet;
  28 extern int sc_width, sc_height;
  29 extern int quit_at_eof;
  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 #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         static void
  56 eof_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
  81 squish_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
  99 forw(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
 274 back(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
 327 forward(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
 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 }