root/src/viewer/ascii.c

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DEFINITIONS

This source file includes following definitions.
  1. mcview_wcwidth
  2. mcview_ismark
  3. mcview_is_non_spacing_mark
  4. mcview_is_spacing_mark
  5. mcview_isprint
  6. mcview_char_display
  7. mcview_get_next_char
  8. mcview_get_next_maybe_nroff_char
  9. mcview_next_combining_char_sequence
  10. mcview_display_line
  11. mcview_display_paragraph
  12. mcview_wrap_fixup
  13. mcview_display_text
  14. mcview_ascii_move_down
  15. mcview_ascii_move_up
  16. mcview_ascii_moveto_bol
  17. mcview_ascii_moveto_eol
  18. mcview_state_machine_init

   1 /*
   2    Internal file viewer for the Midnight Commander
   3    Function for plain view
   4 
   5    Copyright (C) 1994-2021
   6    Free Software Foundation, Inc.
   7 
   8    Written by:
   9    Miguel de Icaza, 1994, 1995, 1998
  10    Janne Kukonlehto, 1994, 1995
  11    Jakub Jelinek, 1995
  12    Joseph M. Hinkle, 1996
  13    Norbert Warmuth, 1997
  14    Pavel Machek, 1998
  15    Roland Illig <roland.illig@gmx.de>, 2004, 2005
  16    Slava Zanko <slavazanko@google.com>, 2009
  17    Andrew Borodin <aborodin@vmail.ru>, 2009-2014
  18    Ilia Maslakov <il.smind@gmail.com>, 2009
  19    Rewritten almost from scratch by:
  20    Egmont Koblinger <egmont@gmail.com>, 2014
  21 
  22    This file is part of the Midnight Commander.
  23 
  24    The Midnight Commander is free software: you can redistribute it
  25    and/or modify it under the terms of the GNU General Public License as
  26    published by the Free Software Foundation, either version 3 of the License,
  27    or (at your option) any later version.
  28 
  29    The Midnight Commander is distributed in the hope that it will be useful,
  30    but WITHOUT ANY WARRANTY; without even the implied warranty of
  31    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  32    GNU General Public License for more details.
  33 
  34    You should have received a copy of the GNU General Public License
  35    along with this program.  If not, see <http://www.gnu.org/licenses/>.
  36 
  37    ------------------------------------------------------------------------------------------------
  38 
  39    The viewer is implemented along the following design principles:
  40 
  41    Goals: Always display simple scripts, double wide (CJK), combining accents and spacing marks
  42    (often used e.g. in Devanagari) perfectly. Make the arrow keys always work correctly.
  43 
  44    Absolutely non-goal: RTL.
  45 
  46    Terminology:
  47 
  48    - A "paragraph" is the text between two adjacent newline characters. A "line" or "row" is a
  49    visual row on the screen. In wrap mode, the viewer formats a paragraph into one or more lines.
  50 
  51    - The Unicode glossary <http://www.unicode.org/glossary/> doesn't seem to have a notion of "base
  52    character followed by zero or more combining characters". The closest matches are "Combining
  53    Character Sequence" meaning a base character followed by one or more combining characters, or
  54    "Grapheme" which seems to exclude non-printable characters such as newline. In this file,
  55    "combining character sequence" (or any obvious abbreviation thereof) means a base character
  56    followed by zero or more (up to a current limit of 4) combining characters.
  57 
  58    ------------------------------------------------------------------------------------------------
  59 
  60    The parser-formatter is designed to be stateless across paragraphs. This is so that we can walk
  61    backwards without having to reparse the whole file (although we still need to reparse and
  62    reformat the whole paragraph, but it's a lot better). This principle needs to be changed if we
  63    ever get to address tickets 1849/2977, but then we can still store (for efficiency) the parser
  64    state at the beginning of the paragraph, and safely walk backwards if we don't cross an escape
  65    character.
  66 
  67    The parser-formatter, however, definitely needs to carry a state across lines. Currently this
  68    state contains:
  69 
  70    - The logical column (as if we didn't wrap). This is used for handling TAB characters after a
  71    wordwrap consistently with less.
  72 
  73    - Whether the last nroff character was bold or underlined. This is used for displaying the
  74    ambiguous _\b_ sequence consistently with less.
  75 
  76    - Whether the desired way of displaying a lonely combining accent or spacing mark is to place it
  77    over a dotted circle (we do this at the beginning of the paragraph of after a TAB), or to ignore
  78    the combining char and show replacement char for the spacing mark (we do this if e.g. too many
  79    of these were encountered and hence we don't glue them with their base character).
  80 
  81    - (This state needs to be expanded if e.g. we decide to print verbose replacement characters
  82    (e.g. "<U+0080>") and allow these to wrap around lines.)
  83 
  84    The state also contains the file offset, as it doesn't make sense to ever know the state without
  85    knowing the corresponding offset.
  86 
  87    The state depends on various settings (viewer width, encoding, nroff mode, charwrap or wordwrap
  88    mode (if we'll have that one day) etc.), needs to be recomputed if any of these changes.
  89 
  90    Walking forwards is usually relatively easy both in the file and on the screen. Walking
  91    backwards within a paragraph would only be possible in some special cases and even then it would
  92    be painful, so we always walk back to the beginning of the paragraph and reparse-reformat from
  93    there.
  94 
  95    (Walking back within a line in the file would have at least the following difficulties: handling
  96    the parser state; processing invalid UTF-8; processing invalid nroff (e.g. what is "_\bA\bA"?).
  97    Walking back on the display: we wouldn't know where to display the last line of a paragraph, or
  98    where to display a line if its following line starts with a wide (CJK or Tab) character. Long
  99    story short: just forget this approach.)
 100 
 101    Most important variables:
 102 
 103    - dpy_start: Both in unwrap and wrap modes this points to the beginning of the topmost displayed
 104    paragraph.
 105 
 106    - dpy_text_column: Only in unwrap mode, an additional horizontal scroll.
 107 
 108    - dpy_paragraph_skip_lines: Only in wrap mode, an additional vertical scroll (the number of
 109    lines that are scrolled off at the top from the topmost paragraph).
 110 
 111    - dpy_state_top: Only in wrap mode, the offset and parser-formatter state at the line where
 112    displaying the file begins is cached here.
 113 
 114    - dpy_wrap_dirty: If some parameter has changed that makes it necessary to reparse-redisplay the
 115    topmost paragraph.
 116 
 117    In wrap mode, the three variables "dpy_start", "dpy_paragraph_skip_lines" and "dpy_state_top"
 118    are kept consistent. Think of the first two as the ones describing the position, and the third
 119    as a cached value for better performance so that we don't need to wrap the invisible beginning
 120    of the topmost paragraph over and over again. The third value needs to be recomputed each time a
 121    parameter that influences parsing or displaying the file (e.g. width of screen, encoding, nroff
 122    mode) changes, this is signaled by "dpy_wrap_dirty" to force recomputing "dpy_state_top" (and
 123    clamp "dpy_paragraph_skip_lines" if necessary).
 124 
 125    ------------------------------------------------------------------------------------------------
 126 
 127    Help integration
 128 
 129    I'm planning to port the help viewer to this codebase.
 130 
 131    Splitting at sections would still happen in the help viewer. It would either copy a section, or
 132    set force_max and a similar force_min to limit displaying to one section only.
 133 
 134    Parsing the help format would go next to the nroff parser. The colors, alternate character set,
 135    and emitting the version number would go to the "state". (The version number would be
 136    implemented by emitting remaining characters of a buffer in the "state" one by one, without
 137    advancing in the file position.)
 138 
 139    The active link would be drawn similarly to the search highlight. Other than that, the viewer
 140    wouldn't care about links (except for their color). help.c would keep track of which one is
 141    highlighted, how to advance to the next/prev on an arrow, how the scroll offset needs to be
 142    adjusted when moving, etc.
 143 
 144    Add wrapping at word boundaries to where wrapping at char boundaries happens now.
 145  */
 146 
 147 #include <config.h>
 148 
 149 #include "lib/global.h"
 150 #include "lib/tty/tty.h"
 151 #include "lib/skin.h"
 152 #include "lib/util.h"           /* is_printable() */
 153 #ifdef HAVE_CHARSET
 154 #include "lib/charsets.h"
 155 #endif
 156 
 157 #include "src/setup.h"          /* option_tab_spacing */
 158 
 159 #include "internal.h"
 160 
 161 /*** global variables ****************************************************************************/
 162 
 163 /*** file scope macro definitions ****************************************************************/
 164 
 165 /* The Unicode standard recommends that lonely combining characters are printed over a dotted
 166  * circle. If the terminal is not UTF-8, this will be replaced by a dot anyway. */
 167 #define BASE_CHARACTER_FOR_LONELY_COMBINING 0x25CC      /* dotted circle */
 168 #define MAX_COMBINING_CHARS 4   /* both slang and ncurses support exactly 4 */
 169 
 170 /* I think anything other than space (e.g. arrows) just introduce visual clutter without actually
 171  * adding value. */
 172 #define PARTIAL_CJK_AT_LEFT_MARGIN  ' '
 173 #define PARTIAL_CJK_AT_RIGHT_MARGIN ' '
 174 
 175 /*
 176  * Wrap mode: This is for safety so that jumping to the end of file (which already includes
 177  * scrolling back by a page) and then walking backwards is reasonably fast, even if the file is
 178  * extremely large and consists of maybe full zeros or something like that. If there's no newline
 179  * found within this limit, just start displaying from there and see what happens. We might get
 180  * some displaying parameteres (most importantly the columns) incorrect, but at least will show the
 181  * file without spinning the CPU for ages. When scrolling back to that point, the user might see a
 182  * garbled first line (even starting with an invalid partial UTF-8), but then walking back by yet
 183  * another line should fix it.
 184  *
 185  * Unwrap mode: This is not used, we wouldn't be able to do anything reasonable without walking
 186  * back a whole paragraph (well, view->data_area.height paragraphs actually).
 187  */
 188 #define MAX_BACKWARDS_WALK_IN_PARAGRAPH (100 * 1000)
 189 
 190 /*** file scope type declarations ****************************************************************/
 191 
 192 /*** file scope variables ************************************************************************/
 193 
 194 /* --------------------------------------------------------------------------------------------- */
 195 /*** file scope functions ************************************************************************/
 196 /* --------------------------------------------------------------------------------------------- */
 197 
 198 /* TODO: These methods shouldn't be necessary, see ticket 3257 */
 199 
 200 static int
 201 mcview_wcwidth (const WView * view, int c)
     /* [previous][next][first][last][top][bottom][index][help]  */
 202 {
 203 #ifdef HAVE_CHARSET
 204     if (view->utf8)
 205     {
 206         if (g_unichar_iswide (c))
 207             return 2;
 208         if (g_unichar_iszerowidth (c))
 209             return 0;
 210     }
 211 #else
 212     (void) view;
 213     (void) c;
 214 #endif /* HAVE_CHARSET */
 215     return 1;
 216 }
 217 
 218 /* --------------------------------------------------------------------------------------------- */
 219 
 220 static gboolean
 221 mcview_ismark (const WView * view, int c)
     /* [previous][next][first][last][top][bottom][index][help]  */
 222 {
 223 #ifdef HAVE_CHARSET
 224     if (view->utf8)
 225         return g_unichar_ismark (c);
 226 #else
 227     (void) view;
 228     (void) c;
 229 #endif /* HAVE_CHARSET */
 230     return FALSE;
 231 }
 232 
 233 /* --------------------------------------------------------------------------------------------- */
 234 
 235 /* actually is_non_spacing_mark_or_enclosing_mark */
 236 static gboolean
 237 mcview_is_non_spacing_mark (const WView * view, int c)
     /* [previous][next][first][last][top][bottom][index][help]  */
 238 {
 239 #ifdef HAVE_CHARSET
 240     if (view->utf8)
 241     {
 242         GUnicodeType type;
 243 
 244         type = g_unichar_type (c);
 245 
 246         return type == G_UNICODE_NON_SPACING_MARK || type == G_UNICODE_ENCLOSING_MARK;
 247     }
 248 #else
 249     (void) view;
 250     (void) c;
 251 #endif /* HAVE_CHARSET */
 252     return FALSE;
 253 }
 254 
 255 /* --------------------------------------------------------------------------------------------- */
 256 
 257 #if 0
 258 static gboolean
 259 mcview_is_spacing_mark (const WView * view, int c)
     /* [previous][next][first][last][top][bottom][index][help]  */
 260 {
 261 #ifdef HAVE_CHARSET
 262     if (view->utf8)
 263         return g_unichar_type (c) == G_UNICODE_SPACING_MARK;
 264 #else
 265     (void) view;
 266     (void) c;
 267 #endif /* HAVE_CHARSET */
 268     return FALSE;
 269 }
 270 #endif /* 0 */
 271 
 272 /* --------------------------------------------------------------------------------------------- */
 273 
 274 static gboolean
 275 mcview_isprint (const WView * view, int c)
     /* [previous][next][first][last][top][bottom][index][help]  */
 276 {
 277 #ifdef HAVE_CHARSET
 278     if (!view->utf8)
 279         c = convert_from_8bit_to_utf_c ((unsigned char) c, view->converter);
 280     return g_unichar_isprint (c);
 281 #else
 282     (void) view;
 283     /* TODO this is very-very buggy by design: ticket 3257 comments 0-1 */
 284     return is_printable (c);
 285 #endif /* HAVE_CHARSET */
 286 }
 287 
 288 /* --------------------------------------------------------------------------------------------- */
 289 
 290 static int
 291 mcview_char_display (const WView * view, int c, char *s)
     /* [previous][next][first][last][top][bottom][index][help]  */
 292 {
 293 #ifdef HAVE_CHARSET
 294     if (mc_global.utf8_display)
 295     {
 296         if (!view->utf8)
 297             c = convert_from_8bit_to_utf_c ((unsigned char) c, view->converter);
 298         if (!g_unichar_isprint (c))
 299             c = '.';
 300         return g_unichar_to_utf8 (c, s);
 301     }
 302     if (view->utf8)
 303     {
 304         if (g_unichar_iswide (c))
 305         {
 306             s[0] = s[1] = '.';
 307             return 2;
 308         }
 309         if (g_unichar_iszerowidth (c))
 310             return 0;
 311         /* TODO the is_printable check below will be broken for this */
 312         c = convert_from_utf_to_current_c (c, view->converter);
 313     }
 314     else
 315     {
 316         /* TODO the is_printable check below will be broken for this */
 317         c = convert_to_display_c (c);
 318     }
 319 #else
 320     (void) view;
 321 #endif /* HAVE_CHARSET */
 322     /* TODO this is very-very buggy by design: ticket 3257 comments 0-1 */
 323     if (!is_printable (c))
 324         c = '.';
 325     *s = c;
 326     return 1;
 327 }
 328 
 329 /* --------------------------------------------------------------------------------------------- */
 330 
 331 /**
 332  * Just for convenience, a common interface in front of mcview_get_utf and mcview_get_byte, so that
 333  * the caller doesn't have to care about utf8 vs 8-bit modes.
 334  *
 335  * Normally: stores c, updates state, returns TRUE.
 336  * At EOF: state is unchanged, c is undefined, returns FALSE.
 337  *
 338  * Just as with mcview_get_utf(), invalid UTF-8 is reported using negative integers.
 339  *
 340  * Also, temporary hack: handle force_max here.
 341  * TODO: move it to lower layers (datasource.c)?
 342  */
 343 static gboolean
 344 mcview_get_next_char (WView * view, mcview_state_machine_t * state, int *c)
     /* [previous][next][first][last][top][bottom][index][help]  */
 345 {
 346     /* Pretend EOF if we reached force_max */
 347     if (view->force_max >= 0 && state->offset >= view->force_max)
 348         return FALSE;
 349 
 350 #ifdef HAVE_CHARSET
 351     if (view->utf8)
 352     {
 353         int char_length = 0;
 354 
 355         if (!mcview_get_utf (view, state->offset, c, &char_length))
 356             return FALSE;
 357         /* Pretend EOF if we crossed force_max */
 358         if (view->force_max >= 0 && state->offset + char_length > view->force_max)
 359             return FALSE;
 360 
 361         state->offset += char_length;
 362         return TRUE;
 363     }
 364 #endif /* HAVE_CHARSET */
 365     if (!mcview_get_byte (view, state->offset, c))
 366         return FALSE;
 367     state->offset++;
 368     return TRUE;
 369 }
 370 
 371 /* --------------------------------------------------------------------------------------------- */
 372 /**
 373  * This function parses the next nroff character and gives it to you along with its desired color,
 374  * so you never have to care about nroff again.
 375  *
 376  * The nroff mode does the backspace trick for every single character (Unicode codepoint). At least
 377  * that's what the GNU groff 1.22 package produces, and that's what less 458 expects. For
 378  * double-wide characters (CJK), still only a single backspace is emitted. For combining accents
 379  * and such, the print-backspace-print step is repeated for the base character and then for each
 380  * accent separately.
 381  *
 382  * So, the right place for this layer is after the bytes are interpreted in UTF-8, but before
 383  * joining a base character with its combining accents.
 384  *
 385  * Normally: stores c and color, updates state, returns TRUE.
 386  * At EOF: state is unchanged, c and color are undefined, returns FALSE.
 387  *
 388  * color can be null if the caller doesn't care.
 389  */
 390 static gboolean
 391 mcview_get_next_maybe_nroff_char (WView * view, mcview_state_machine_t * state, int *c, int *color)
     /* [previous][next][first][last][top][bottom][index][help]  */
 392 {
 393     mcview_state_machine_t state_after_nroff;
 394     int c2, c3;
 395 
 396     if (color != NULL)
 397         *color = VIEW_NORMAL_COLOR;
 398 
 399     if (!view->mode_flags.nroff)
 400         return mcview_get_next_char (view, state, c);
 401 
 402     if (!mcview_get_next_char (view, state, c))
 403         return FALSE;
 404     /* Don't allow nroff formatting around CR, LF, TAB or other special chars */
 405     if (!mcview_isprint (view, *c))
 406         return TRUE;
 407 
 408     state_after_nroff = *state;
 409 
 410     if (!mcview_get_next_char (view, &state_after_nroff, &c2))
 411         return TRUE;
 412     if (c2 != '\b')
 413         return TRUE;
 414 
 415     if (!mcview_get_next_char (view, &state_after_nroff, &c3))
 416         return TRUE;
 417     if (!mcview_isprint (view, c3))
 418         return TRUE;
 419 
 420     if (*c == '_' && c3 == '_')
 421     {
 422         *state = state_after_nroff;
 423         if (color != NULL)
 424             *color =
 425                 state->nroff_underscore_is_underlined ? VIEW_UNDERLINED_COLOR : VIEW_BOLD_COLOR;
 426     }
 427     else if (*c == c3)
 428     {
 429         *state = state_after_nroff;
 430         state->nroff_underscore_is_underlined = FALSE;
 431         if (color != NULL)
 432             *color = VIEW_BOLD_COLOR;
 433     }
 434     else if (*c == '_')
 435     {
 436         *c = c3;
 437         *state = state_after_nroff;
 438         state->nroff_underscore_is_underlined = TRUE;
 439         if (color != NULL)
 440             *color = VIEW_UNDERLINED_COLOR;
 441     }
 442 
 443     return TRUE;
 444 }
 445 
 446 /* --------------------------------------------------------------------------------------------- */
 447 /**
 448  * Get one base character, along with its combining or spacing mark characters.
 449  *
 450  * (A spacing mark is a character that extends the base character's width 1 into a combined
 451  * character of width 2, yet these two character cells should not be separated. E.g. Devanagari
 452  * <U+0939><U+094B>.)
 453  *
 454  * This method exists mainly for two reasons. One is to be able to tell if we fit on the current
 455  * line or need to wrap to the next one. The other is that both slang and ncurses seem to require
 456  * that the character and its combining marks are printed in a single call (or is it just a
 457  * limitation of mc's wrapper to them?).
 458  *
 459  * For convenience, this method takes care of converting CR or CR+LF into LF.
 460  * TODO this should probably happen later, when displaying the file?
 461  *
 462  * Normally: stores cs and color, updates state, returns >= 1 (entries in cs).
 463  * At EOF: state is unchanged, cs and color are undefined, returns 0.
 464  *
 465  * @param view ...
 466  * @param state the parser-formatter state machine's state, updated
 467  * @param cs store the characters here
 468  * @param clen the room available in cs (that is, at most clen-1 combining marks are allowed), must
 469  *   be at least 2
 470  * @param color if non-NULL, store the color here, taken from the first codepoint's color
 471  * @return the number of entries placed in cs, or 0 on EOF
 472  */
 473 static int
 474 mcview_next_combining_char_sequence (WView * view, mcview_state_machine_t * state, int *cs,
     /* [previous][next][first][last][top][bottom][index][help]  */
 475                                      int clen, int *color)
 476 {
 477     int i = 1;
 478 
 479     if (!mcview_get_next_maybe_nroff_char (view, state, cs, color))
 480         return 0;
 481 
 482     /* Process \r and \r\n newlines. */
 483     if (cs[0] == '\r')
 484     {
 485         int cnext;
 486 
 487         mcview_state_machine_t state_after_crlf = *state;
 488         if (mcview_get_next_maybe_nroff_char (view, &state_after_crlf, &cnext, NULL)
 489             && cnext == '\n')
 490             *state = state_after_crlf;
 491         cs[0] = '\n';
 492         return 1;
 493     }
 494 
 495     /* We don't want combining over non-printable characters. This includes '\n' and '\t' too. */
 496     if (!mcview_isprint (view, cs[0]))
 497         return 1;
 498 
 499     if (mcview_ismark (view, cs[0]))
 500     {
 501         if (!state->print_lonely_combining)
 502         {
 503             /* First character is combining. Either just return it, ... */
 504             return 1;
 505         }
 506         else
 507         {
 508             /* or place this (and subsequent combining ones) over a dotted circle. */
 509             cs[1] = cs[0];
 510             cs[0] = BASE_CHARACTER_FOR_LONELY_COMBINING;
 511             i = 2;
 512         }
 513     }
 514 
 515     if (mcview_wcwidth (view, cs[0]) == 2)
 516     {
 517         /* Don't allow combining or spacing mark for wide characters, is this okay? */
 518         return 1;
 519     }
 520 
 521     /* Look for more combining chars. Either at most clen-1 zero-width combining chars,
 522      * or at most 1 spacing mark. Is this logic correct? */
 523     for (; i < clen; i++)
 524     {
 525         mcview_state_machine_t state_after_combining;
 526 
 527         state_after_combining = *state;
 528         if (!mcview_get_next_maybe_nroff_char (view, &state_after_combining, &cs[i], NULL))
 529             return i;
 530         if (!mcview_ismark (view, cs[i]) || !mcview_isprint (view, cs[i]))
 531             return i;
 532         if (g_unichar_type (cs[i]) == G_UNICODE_SPACING_MARK)
 533         {
 534             /* Only allow as the first combining char. Stop processing in either case. */
 535             if (i == 1)
 536             {
 537                 *state = state_after_combining;
 538                 i++;
 539             }
 540             return i;
 541         }
 542         *state = state_after_combining;
 543     }
 544     return i;
 545 }
 546 
 547 /* --------------------------------------------------------------------------------------------- */
 548 /**
 549  * Parse, format and possibly display one visual line of text.
 550  *
 551  * Formatting starts at the given "state" (which encodes the file offset and parser and formatter's
 552  * internal state). In unwrap mode, this should point to the beginning of the paragraph with the
 553  * default state, the additional horizontal scrolling is added here. In wrap mode, this should
 554  * point to the beginning of the line, with the proper state at that point.
 555  *
 556  * In wrap mode, if a line ends in a newline, it is consumed, even if it's exactly at the right
 557  * edge. In unwrap mode, the whole remaining line, including the newline is consumed. Displaying
 558  * the next line should start at "state"'s new value, or if we displayed the bottom line then
 559  * state->offset tells the file offset to be shown in the top bar.
 560  *
 561  * If "row" is offscreen, don't actually display the line but still update "state" and return the
 562  * proper value. This is used by mcview_wrap_move_down to advance in the file.
 563  *
 564  * @param view ...
 565  * @param state the parser-formatter state machine's state, updated
 566  * @param row print to this row
 567  * @param paragraph_ended store TRUE if paragraph ended by newline or EOF, FALSE if wraps to next
 568  *   line
 569  * @param linewidth store the width of the line here
 570  * @return the number of rows, that is, 0 if we were already at EOF, otherwise 1
 571  */
 572 static int
 573 mcview_display_line (WView * view, mcview_state_machine_t * state, int row,
     /* [previous][next][first][last][top][bottom][index][help]  */
 574                      gboolean * paragraph_ended, off_t * linewidth)
 575 {
 576     const screen_dimen left = view->data_area.left;
 577     const screen_dimen top = view->data_area.top;
 578     const screen_dimen width = view->data_area.width;
 579     const screen_dimen height = view->data_area.height;
 580     off_t dpy_text_column = view->mode_flags.wrap ? 0 : view->dpy_text_column;
 581     screen_dimen col = 0;
 582     int cs[1 + MAX_COMBINING_CHARS];
 583     char str[(1 + MAX_COMBINING_CHARS) * UTF8_CHAR_LEN + 1];
 584     int i, j;
 585 
 586     if (paragraph_ended != NULL)
 587         *paragraph_ended = TRUE;
 588 
 589     if (!view->mode_flags.wrap && (row < 0 || row >= (int) height) && linewidth == NULL)
 590     {
 591         /* Optimization: Fast forward to the end of the line, rather than carefully
 592          * parsing and then not actually displaying it. */
 593         off_t eol;
 594         int retval;
 595 
 596         eol = mcview_eol (view, state->offset);
 597         retval = (eol > state->offset) ? 1 : 0;
 598 
 599         mcview_state_machine_init (state, eol);
 600         return retval;
 601     }
 602 
 603     while (TRUE)
 604     {
 605         int charwidth = 0;
 606         mcview_state_machine_t state_saved;
 607         int n;
 608         int color;
 609 
 610         state_saved = *state;
 611         n = mcview_next_combining_char_sequence (view, state, cs, 1 + MAX_COMBINING_CHARS, &color);
 612         if (n == 0)
 613         {
 614             if (linewidth != NULL)
 615                 *linewidth = col;
 616             return (col > 0) ? 1 : 0;
 617         }
 618 
 619         if (view->search_start <= state->offset && state->offset < view->search_end)
 620             color = VIEW_SELECTED_COLOR;
 621 
 622         if (cs[0] == '\n')
 623         {
 624             /* New line: reset all formatting state for the next paragraph. */
 625             mcview_state_machine_init (state, state->offset);
 626             if (linewidth != NULL)
 627                 *linewidth = col;
 628             return 1;
 629         }
 630 
 631         if (mcview_is_non_spacing_mark (view, cs[0]))
 632         {
 633             /* Lonely combining character. Probably leftover after too many combining chars. Just ignore. */
 634             continue;
 635         }
 636 
 637         /* Nonprintable, or lonely spacing mark */
 638         if ((!mcview_isprint (view, cs[0]) || mcview_ismark (view, cs[0])) && cs[0] != '\t')
 639             cs[0] = '.';
 640 
 641         for (i = 0; i < n; i++)
 642             charwidth += mcview_wcwidth (view, cs[i]);
 643 
 644         /* Adjust the width for TAB. It's handled below along with the normal characters,
 645          * so that it's wrapped consistently with them, and is painted with the proper
 646          * attributes (although currently it can't have a special color). */
 647         if (cs[0] == '\t')
 648         {
 649             charwidth = option_tab_spacing - state->unwrapped_column % option_tab_spacing;
 650             state->print_lonely_combining = TRUE;
 651         }
 652         else
 653             state->print_lonely_combining = FALSE;
 654 
 655         /* In wrap mode only: We're done with this row if the character sequence wouldn't fit.
 656          * Except if at the first column, because then it wouldn't fit in the next row either.
 657          * In this extreme case let the unwrapped code below do its best to display it. */
 658         if (view->mode_flags.wrap && (off_t) col + charwidth > dpy_text_column + (off_t) width
 659             && col > 0)
 660         {
 661             *state = state_saved;
 662             if (paragraph_ended != NULL)
 663                 *paragraph_ended = FALSE;
 664             if (linewidth != NULL)
 665                 *linewidth = col;
 666             return 1;
 667         }
 668 
 669         /* Display, unless outside of the viewport. */
 670         if (row >= 0 && row < (int) height)
 671         {
 672             if ((off_t) col >= dpy_text_column &&
 673                 (off_t) col + charwidth <= dpy_text_column + (off_t) width)
 674             {
 675                 /* The combining character sequence fits entirely in the viewport. Print it. */
 676                 tty_setcolor (color);
 677                 widget_gotoyx (view, top + row, left + ((off_t) col - dpy_text_column));
 678                 if (cs[0] == '\t')
 679                 {
 680                     for (i = 0; i < charwidth; i++)
 681                         tty_print_char (' ');
 682                 }
 683                 else
 684                 {
 685                     j = 0;
 686                     for (i = 0; i < n; i++)
 687                         j += mcview_char_display (view, cs[i], str + j);
 688                     str[j] = '\0';
 689                     /* This is probably a bug in our tty layer, but tty_print_string
 690                      * normalizes the string, whereas tty_printf doesn't. Don't normalize,
 691                      * since we handle combining characters ourselves correctly, it's
 692                      * better if they are copy-pasted correctly. Ticket 3255. */
 693                     tty_printf ("%s", str);
 694                 }
 695             }
 696             else if ((off_t) col < dpy_text_column && (off_t) col + charwidth > dpy_text_column)
 697             {
 698                 /* The combining character sequence would cross the left edge of the viewport.
 699                  * This cannot happen with wrap mode. Print replacement character(s),
 700                  * or spaces with the correct attributes for partial Tabs. */
 701                 tty_setcolor (color);
 702                 for (i = dpy_text_column;
 703                      i < (off_t) col + charwidth && i < dpy_text_column + (off_t) width; i++)
 704                 {
 705                     widget_gotoyx (view, top + row, left + (i - dpy_text_column));
 706                     tty_print_anychar ((cs[0] == '\t') ? ' ' : PARTIAL_CJK_AT_LEFT_MARGIN);
 707                 }
 708             }
 709             else if ((off_t) col < dpy_text_column + (off_t) width &&
 710                      (off_t) col + charwidth > dpy_text_column + (off_t) width)
 711             {
 712                 /* The combining character sequence would cross the right edge of the viewport
 713                  * and we're not wrapping. Print replacement character(s),
 714                  * or spaces with the correct attributes for partial Tabs. */
 715                 tty_setcolor (color);
 716                 for (i = col; i < dpy_text_column + (off_t) width; i++)
 717                 {
 718                     widget_gotoyx (view, top + row, left + (i - dpy_text_column));
 719                     tty_print_anychar ((cs[0] == '\t') ? ' ' : PARTIAL_CJK_AT_RIGHT_MARGIN);
 720                 }
 721             }
 722         }
 723 
 724         col += charwidth;
 725         state->unwrapped_column += charwidth;
 726 
 727         if (!view->mode_flags.wrap && (off_t) col >= dpy_text_column + (off_t) width
 728             && linewidth == NULL)
 729         {
 730             /* Optimization: Fast forward to the end of the line, rather than carefully
 731              * parsing and then not actually displaying it. */
 732             off_t eol;
 733 
 734             eol = mcview_eol (view, state->offset);
 735             mcview_state_machine_init (state, eol);
 736             return 1;
 737         }
 738     }
 739 }
 740 
 741 /* --------------------------------------------------------------------------------------------- */
 742 /**
 743  * Parse, format and possibly display one paragraph (perhaps not from the beginning).
 744  *
 745  * Formatting starts at the given "state" (which encodes the file offset and parser and formatter's
 746  * internal state). In unwrap mode, this should point to the beginning of the paragraph with the
 747  * default state, the additional horizontal scrolling is added here. In wrap mode, this may point
 748  * to the beginning of the line within a paragraph (to display the partial paragraph at the top),
 749  * with the proper state at that point.
 750  *
 751  * Displaying the next paragraph should start at "state"'s new value, or if we displayed the bottom
 752  * line then state->offset tells the file offset to be shown in the top bar.
 753  *
 754  * If "row" is negative, don't display the first abs(row) lines and display the rest from the top.
 755  * This was a nice idea but it's now unused :)
 756  *
 757  * If "row" is too large, don't display the paragraph at all but still return the number of lines.
 758  * This is used when moving upwards.
 759  *
 760  * @param view ...
 761  * @param state the parser-formatter state machine's state, updated
 762  * @param row print starting at this row
 763  * @return the number of rows the paragraphs is wrapped to, that is, 0 if we were already at EOF,
 764  *   otherwise 1 in unwrap mode, >= 1 in wrap mode. We stop when reaching the bottom of the
 765  *   viewport, it's not counted how many more lines the paragraph would occupy
 766  */
 767 static int
 768 mcview_display_paragraph (WView * view, mcview_state_machine_t * state, int row)
     /* [previous][next][first][last][top][bottom][index][help]  */
 769 {
 770     const screen_dimen height = view->data_area.height;
 771     int lines = 0;
 772 
 773     while (TRUE)
 774     {
 775         gboolean paragraph_ended;
 776 
 777         lines += mcview_display_line (view, state, row, &paragraph_ended, NULL);
 778         if (paragraph_ended)
 779             return lines;
 780 
 781         if (row < (int) height)
 782         {
 783             row++;
 784             /* stop if bottom of screen reached */
 785             if (row >= (int) height)
 786                 return lines;
 787         }
 788     }
 789 }
 790 
 791 /* --------------------------------------------------------------------------------------------- */
 792 /**
 793  * Recompute dpy_state_top from dpy_start and dpy_paragraph_skip_lines. Clamp
 794  * dpy_paragraph_skip_lines if necessary.
 795  *
 796  * This method should be called in wrap mode after changing one of the parsing or formatting
 797  * properties (e.g. window width, encoding, nroff), or when switching to wrap mode from unwrap or
 798  * hex.
 799  *
 800  * If we stayed within the same paragraph then try to keep the vertical offset within that
 801  * paragraph as well. It might happen though that the paragraph became shorter than our desired
 802  * vertical position, in that case move to its last row.
 803  */
 804 static void
 805 mcview_wrap_fixup (WView * view)
     /* [previous][next][first][last][top][bottom][index][help]  */
 806 {
 807     int lines = view->dpy_paragraph_skip_lines;
 808 
 809     if (!view->dpy_wrap_dirty)
 810         return;
 811     view->dpy_wrap_dirty = FALSE;
 812 
 813     view->dpy_paragraph_skip_lines = 0;
 814     mcview_state_machine_init (&view->dpy_state_top, view->dpy_start);
 815 
 816     while (lines-- != 0)
 817     {
 818         mcview_state_machine_t state_prev;
 819         gboolean paragraph_ended;
 820 
 821         state_prev = view->dpy_state_top;
 822         if (mcview_display_line (view, &view->dpy_state_top, -1, &paragraph_ended, NULL) == 0)
 823             break;
 824         if (paragraph_ended)
 825         {
 826             view->dpy_state_top = state_prev;
 827             break;
 828         }
 829         view->dpy_paragraph_skip_lines++;
 830     }
 831 }
 832 
 833 /* --------------------------------------------------------------------------------------------- */
 834 /*** public functions ****************************************************************************/
 835 /* --------------------------------------------------------------------------------------------- */
 836 
 837 /**
 838  * In both wrap and unwrap modes, dpy_start points to the beginning of the paragraph.
 839  *
 840  * In unwrap mode, start displaying from this position, probably applying an additional horizontal
 841  * scroll.
 842  *
 843  * In wrap mode, an additional dpy_paragraph_skip_lines lines are skipped from the top of this
 844  * paragraph. dpy_state_top contains the position and parser-formatter state corresponding to the
 845  * top left corner so we can just start rendering from here. Unless dpy_wrap_dirty is set in which
 846  * case dpy_state_top is invalid and we need to recompute first.
 847  */
 848 void
 849 mcview_display_text (WView * view)
     /* [previous][next][first][last][top][bottom][index][help]  */
 850 {
 851     const screen_dimen left = view->data_area.left;
 852     const screen_dimen top = view->data_area.top;
 853     const screen_dimen height = view->data_area.height;
 854     int row;
 855     mcview_state_machine_t state;
 856     gboolean again;
 857 
 858     do
 859     {
 860         int n;
 861 
 862         again = FALSE;
 863 
 864         mcview_display_clean (view);
 865         mcview_display_ruler (view);
 866 
 867         if (!view->mode_flags.wrap)
 868             mcview_state_machine_init (&state, view->dpy_start);
 869         else
 870         {
 871             mcview_wrap_fixup (view);
 872             state = view->dpy_state_top;
 873         }
 874 
 875         for (row = 0; row < (int) height; row += n)
 876         {
 877             n = mcview_display_paragraph (view, &state, row);
 878             if (n == 0)
 879             {
 880                 /* In the rare case that displaying didn't start at the beginning
 881                  * of the file, yet there are some empty lines at the bottom,
 882                  * scroll the file and display again. This happens when e.g. the
 883                  * window is made bigger, or the file becomes shorter due to
 884                  * charset change or enabling nroff. */
 885                 if ((view->mode_flags.wrap ? view->dpy_state_top.offset : view->dpy_start) > 0)
 886                 {
 887                     mcview_ascii_move_up (view, height - row);
 888                     again = TRUE;
 889                 }
 890                 break;
 891             }
 892         }
 893     }
 894     while (again);
 895 
 896     view->dpy_end = state.offset;
 897     view->dpy_state_bottom = state;
 898 
 899     tty_setcolor (VIEW_NORMAL_COLOR);
 900     if (mcview_show_eof != NULL && mcview_show_eof[0] != '\0')
 901         while (row < (int) height)
 902         {
 903             widget_gotoyx (view, top + row, left);
 904             /* TODO: should make it no wider than the viewport */
 905             tty_print_string (mcview_show_eof);
 906             row++;
 907         }
 908 }
 909 
 910 /* --------------------------------------------------------------------------------------------- */
 911 /**
 912  * Move down.
 913  *
 914  * It's very simple. Just invisibly format the next "lines" lines, carefully carrying the formatter
 915  * state in wrap mode. But before each step we need to check if we've already hit the end of the
 916  * file, in that case we can no longer move. This is done by walking from dpy_state_bottom.
 917  *
 918  * Note that this relies on mcview_display_text() setting dpy_state_bottom to its correct value
 919  * upon rendering the screen contents. So don't call this function from other functions (e.g. at
 920  * the bottom of mcview_ascii_move_up()) which invalidate this value.
 921  */
 922 void
 923 mcview_ascii_move_down (WView * view, off_t lines)
     /* [previous][next][first][last][top][bottom][index][help]  */
 924 {
 925     while (lines-- != 0)
 926     {
 927         gboolean paragraph_ended;
 928 
 929         /* See if there's still data below the bottom line, by imaginarily displaying one
 930          * more line. This takes care of reading more data into growbuf, if required.
 931          * If the end position didn't advance, we're at EOF and hence bail out. */
 932         if (mcview_display_line (view, &view->dpy_state_bottom, -1, &paragraph_ended, NULL) == 0)
 933             break;
 934 
 935         /* Okay, there's enough data. Move by 1 row at the top, too. No need to check for
 936          * EOF, that can't happen. */
 937         if (!view->mode_flags.wrap)
 938         {
 939             view->dpy_start = mcview_eol (view, view->dpy_start);
 940             view->dpy_paragraph_skip_lines = 0;
 941             view->dpy_wrap_dirty = TRUE;
 942         }
 943         else
 944         {
 945             mcview_display_line (view, &view->dpy_state_top, -1, &paragraph_ended, NULL);
 946             if (!paragraph_ended)
 947                 view->dpy_paragraph_skip_lines++;
 948             else
 949             {
 950                 view->dpy_start = view->dpy_state_top.offset;
 951                 view->dpy_paragraph_skip_lines = 0;
 952             }
 953         }
 954     }
 955 }
 956 
 957 /* --------------------------------------------------------------------------------------------- */
 958 /**
 959  * Move up.
 960  *
 961  * Unwrap mode: Piece of cake. Wrap mode: If we'd walk back more than the current line offset
 962  * within the paragraph, we need to jump back to the previous paragraph and compute its height to
 963  * see if we start from that paragraph, and repeat this if necessary. Once we're within the desired
 964  * paragraph, we still need to format it from its beginning to know the state.
 965  *
 966  * See the top of this file for comments about MAX_BACKWARDS_WALK_IN_PARAGRAPH.
 967  *
 968  * force_max is a nice protection against the rare extreme case that the file underneath us
 969  * changes, we don't want to endlessly consume a file of maybe full of zeros upon moving upwards.
 970  */
 971 void
 972 mcview_ascii_move_up (WView * view, off_t lines)
     /* [previous][next][first][last][top][bottom][index][help]  */
 973 {
 974     if (!view->mode_flags.wrap)
 975     {
 976         while (lines-- != 0)
 977             view->dpy_start = mcview_bol (view, view->dpy_start - 1, 0);
 978         view->dpy_paragraph_skip_lines = 0;
 979         view->dpy_wrap_dirty = TRUE;
 980     }
 981     else
 982     {
 983         int i;
 984 
 985         while (lines > view->dpy_paragraph_skip_lines)
 986         {
 987             /* We need to go back to the previous paragraph. */
 988             if (view->dpy_start == 0)
 989             {
 990                 /* Oops, we're already in the first paragraph. */
 991                 view->dpy_paragraph_skip_lines = 0;
 992                 mcview_state_machine_init (&view->dpy_state_top, 0);
 993                 return;
 994             }
 995             lines -= view->dpy_paragraph_skip_lines;
 996             view->force_max = view->dpy_start;
 997             view->dpy_start =
 998                 mcview_bol (view, view->dpy_start - 1,
 999                             view->dpy_start - MAX_BACKWARDS_WALK_IN_PARAGRAPH);
1000             mcview_state_machine_init (&view->dpy_state_top, view->dpy_start);
1001             /* This is a tricky way of denoting that we're at the end of the paragraph.
1002              * Normally we'd jump to the next paragraph and reset paragraph_skip_lines. But for
1003              * walking backwards this is exactly what we need. */
1004             view->dpy_paragraph_skip_lines =
1005                 mcview_display_paragraph (view, &view->dpy_state_top, view->data_area.height);
1006             view->force_max = -1;
1007         }
1008 
1009         /* Okay, we have have dpy_start pointing to the desired paragraph, and we still need to
1010          * walk back "lines" lines from the current "dpy_paragraph_skip_lines" offset. We can't do
1011          * that, so walk from the beginning of the paragraph. */
1012         mcview_state_machine_init (&view->dpy_state_top, view->dpy_start);
1013         view->dpy_paragraph_skip_lines -= lines;
1014         for (i = 0; i < view->dpy_paragraph_skip_lines; i++)
1015             mcview_display_line (view, &view->dpy_state_top, -1, NULL, NULL);
1016     }
1017 }
1018 
1019 /* --------------------------------------------------------------------------------------------- */
1020 
1021 void
1022 mcview_ascii_moveto_bol (WView * view)
     /* [previous][next][first][last][top][bottom][index][help]  */
1023 {
1024     if (!view->mode_flags.wrap)
1025         view->dpy_text_column = 0;
1026 }
1027 
1028 /* --------------------------------------------------------------------------------------------- */
1029 
1030 void
1031 mcview_ascii_moveto_eol (WView * view)
     /* [previous][next][first][last][top][bottom][index][help]  */
1032 {
1033     if (!view->mode_flags.wrap)
1034     {
1035         mcview_state_machine_t state;
1036         off_t linewidth;
1037 
1038         /* Get the width of the topmost paragraph. */
1039         mcview_state_machine_init (&state, view->dpy_start);
1040         mcview_display_line (view, &state, -1, NULL, &linewidth);
1041         view->dpy_text_column = DOZ (linewidth, (off_t) view->data_area.width);
1042     }
1043 }
1044 
1045 /* --------------------------------------------------------------------------------------------- */
1046 
1047 void
1048 mcview_state_machine_init (mcview_state_machine_t * state, off_t offset)
     /* [previous][next][first][last][top][bottom][index][help]  */
1049 {
1050     memset (state, 0, sizeof (*state));
1051     state->offset = offset;
1052     state->print_lonely_combining = TRUE;
1053 }
1054 
1055 /* --------------------------------------------------------------------------------------------- */

/* [previous][next][first][last][top][bottom][index][help]  */