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forwback.c

/*
 * Copyright (C) 1984-2002  Mark Nudelman
 *
 * You may distribute under the terms of either the GNU General Public
 * License or the Less License, as specified in the README file.
 *
 * For more information about less, or for information on how to 
 * contact the author, see the README file.
 */


/*
 * Primitives for displaying the file on the screen,
 * scrolling either forward or backward.
 */

#include "less.h"
#include "position.h"

public int hit_eof;     /* Keeps track of how many times we hit end of file */
public int screen_trashed;
public int squished;
public int no_back_scroll = 0;

extern int sigs;
extern int top_scroll;
extern int quiet;
extern int sc_width, sc_height;
extern int quit_at_eof;
extern int plusoption;
extern int forw_scroll;
extern int back_scroll;
extern int ignore_eoi;
extern int clear_bg;
extern int final_attr;
#if TAGS
extern char *tagoption;
#endif

/*
 * Sound the bell to indicate user is trying to move past end of file.
 */
      static void
eof_bell()
{
      if (quiet == NOT_QUIET)
            bell();
      else
            vbell();
}

/*
 * Check to see if the end of file is currently "displayed".
 */
      static void
eof_check()
{
      POSITION pos;

      if (ignore_eoi)
            return;
      if (ABORT_SIGS())
            return;
      /*
       * If the bottom line is empty, we are at EOF.
       * If the bottom line ends at the file length,
       * we must be just at EOF.
       */
      pos = position(BOTTOM_PLUS_ONE);
      if (pos == NULL_POSITION || pos == ch_length())
            hit_eof++;
}

/*
 * If the screen is "squished", repaint it.
 * "Squished" means the first displayed line is not at the top
 * of the screen; this can happen when we display a short file
 * for the first time.
 */
      static void
squish_check()
{
      if (!squished)
            return;
      squished = 0;
      repaint();
}

/*
 * Display n lines, scrolling forward, 
 * starting at position pos in the input file.
 * "force" means display the n lines even if we hit end of file.
 * "only_last" means display only the last screenful if n > screen size.
 * "nblank" is the number of blank lines to draw before the first
 *   real line.  If nblank > 0, the pos must be NULL_POSITION.
 *   The first real line after the blanks will start at ch_zero().
 */
      public void
forw(n, pos, force, only_last, nblank)
      register int n;
      POSITION pos;
      int force;
      int only_last;
      int nblank;
{
      int eof = 0;
      int nlines = 0;
      int do_repaint;
      static int first_time = 1;

      squish_check();

      /*
       * do_repaint tells us not to display anything till the end, 
       * then just repaint the entire screen.
       * We repaint if we are supposed to display only the last 
       * screenful and the request is for more than a screenful.
       * Also if the request exceeds the forward scroll limit
       * (but not if the request is for exactly a screenful, since
       * repainting itself involves scrolling forward a screenful).
       */
      do_repaint = (only_last && n > sc_height-1) || 
            (forw_scroll >= 0 && n > forw_scroll && n != sc_height-1);

      if (!do_repaint)
      {
            /*
             * Forget any current line shift we might have
             * (from the last line of the previous screenful).
             */
            extern int cshift;
            cshift = 0;

            if (top_scroll && n >= sc_height - 1 && pos != ch_length())
            {
                  /*
                   * Start a new screen.
                   * {{ This is not really desirable if we happen
                   *    to hit eof in the middle of this screen,
                   *    but we don't yet know if that will happen. }}
                   */
                  pos_clear();
                  add_forw_pos(pos);
                  force = 1;
                  if (top_scroll == OPT_ONPLUS || first_time)
                        clear();
                  home();
            } else
            {
                  clear_bot();
            }

            if (pos != position(BOTTOM_PLUS_ONE) || empty_screen())
            {
                  /*
                   * This is not contiguous with what is
                   * currently displayed.  Clear the screen image 
                   * (position table) and start a new screen.
                   */
                  pos_clear();
                  add_forw_pos(pos);
                  force = 1;
                  if (top_scroll)
                  {
                        if (top_scroll == OPT_ONPLUS)
                              clear();
                        home();
                  } else if (!first_time)
                  {
                        putstr("...skipping...\n");
                  }
            }
      }

      while (--n >= 0)
      {
            /*
             * Read the next line of input.
             */
            if (nblank > 0)
            {
                  /*
                   * Still drawing blanks; don't get a line 
                   * from the file yet.
                   * If this is the last blank line, get ready to
                   * read a line starting at ch_zero() next time.
                   */
                  if (--nblank == 0)
                        pos = ch_zero();
            } else
            {
                  /* 
                   * Get the next line from the file.
                   */
                  pos = forw_line(pos);
                  if (pos == NULL_POSITION)
                  {
                        /*
                         * End of file: stop here unless the top line 
                         * is still empty, or "force" is true.
                         * Even if force is true, stop when the last
                         * line in the file reaches the top of screen.
                         */
                        eof = 1;
                        if (!force && position(TOP) != NULL_POSITION)
                              break;
                        if (!empty_lines(0, 0) && 
                            !empty_lines(1, 1) &&
                             empty_lines(2, sc_height-1))
                              break;
                  }
            }
            /*
             * Add the position of the next line to the position table.
             * Display the current line on the screen.
             */
            add_forw_pos(pos);
            nlines++;
            if (do_repaint)
                  continue;
            /*
             * If this is the first screen displayed and
             * we hit an early EOF (i.e. before the requested
             * number of lines), we "squish" the display down
             * at the bottom of the screen.
             * But don't do this if a + option or a -t option
             * was given.  These options can cause us to
             * start the display after the beginning of the file,
             * and it is not appropriate to squish in that case.
             */
            if (first_time && pos == NULL_POSITION && !top_scroll && 
#if TAGS
                tagoption == NULL &&
#endif
                !plusoption)
            {
                  squished = 1;
                  continue;
            }
            if (top_scroll == OPT_ON)
                  clear_eol();
            put_line();
            if (clear_bg && final_attr != AT_NORMAL)
            {
                  /*
                   * Writing the last character on the last line
                   * of the display may have scrolled the screen.
                   * If we were in standout mode, clear_bg terminals 
                   * will fill the new line with the standout color.
                   * Now we're in normal mode again, so clear the line.
                   */
                  clear_eol();
            }
      }

      if (ignore_eoi)
            hit_eof = 0;
      else if (eof && !ABORT_SIGS())
            hit_eof++;
      else
            eof_check();
      if (nlines == 0)
            eof_bell();
      else if (do_repaint)
            repaint();
      first_time = 0;
      (void) currline(BOTTOM);
}

/*
 * Display n lines, scrolling backward.
 */
      public void
back(n, pos, force, only_last)
      register int n;
      POSITION pos;
      int force;
      int only_last;
{
      int nlines = 0;
      int do_repaint;

      squish_check();
      do_repaint = (n > get_back_scroll() || (only_last && n > sc_height-1));
      hit_eof = 0;
      while (--n >= 0)
      {
            /*
             * Get the previous line of input.
             */
            pos = back_line(pos);
            if (pos == NULL_POSITION)
            {
                  /*
                   * Beginning of file: stop here unless "force" is true.
                   */
                  if (!force)
                        break;
            }
            /*
             * Add the position of the previous line to the position table.
             * Display the line on the screen.
             */
            add_back_pos(pos);
            nlines++;
            if (!do_repaint)
            {
                  home();
                  add_line();
                  put_line();
            }
      }

      eof_check();
      if (nlines == 0)
            eof_bell();
      else if (do_repaint)
            repaint();
      (void) currline(BOTTOM);
}

/*
 * Display n more lines, forward.
 * Start just after the line currently displayed at the bottom of the screen.
 */
      public void
forward(n, force, only_last)
      int n;
      int force;
      int only_last;
{
      POSITION pos;

      if (quit_at_eof && hit_eof && !(ch_getflags() & CH_HELPFILE))
      {
            /*
             * If the -e flag is set and we're trying to go
             * forward from end-of-file, go on to the next file.
             */
            if (edit_next(1))
                  quit(QUIT_OK);
            return;
      }

      pos = position(BOTTOM_PLUS_ONE);
      if (pos == NULL_POSITION && (!force || empty_lines(2, sc_height-1)))
      {
            if (ignore_eoi)
            {
                  /*
                   * ignore_eoi is to support A_F_FOREVER.
                   * Back up until there is a line at the bottom
                   * of the screen.
                   */
                  if (empty_screen())
                        pos = ch_zero();
                  else
                  {
                        do
                        {
                              back(1, position(TOP), 1, 0);
                              pos = position(BOTTOM_PLUS_ONE);
                        } while (pos == NULL_POSITION);
                  }
            } else
            {
                  eof_bell();
                  hit_eof++;
                  return;
            }
      }
      forw(n, pos, force, only_last, 0);
}

/*
 * Display n more lines, backward.
 * Start just before the line currently displayed at the top of the screen.
 */
      public void
backward(n, force, only_last)
      int n;
      int force;
      int only_last;
{
      POSITION pos;

      pos = position(TOP);
      if (pos == NULL_POSITION && (!force || position(BOTTOM) == 0))
      {
            eof_bell();
            return;   
      }
      back(n, pos, force, only_last);
}

/*
 * Get the backwards scroll limit.
 * Must call this function instead of just using the value of
 * back_scroll, because the default case depends on sc_height and
 * top_scroll, as well as back_scroll.
 */
      public int
get_back_scroll()
{
      if (no_back_scroll)
            return (0);
      if (back_scroll >= 0)
            return (back_scroll);
      if (top_scroll)
            return (sc_height - 2);
      return (10000); /* infinity */
}

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