forwback.c

/*
 * Copyright (C) 1984-2022  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, 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 screen_trashed;
public int squished;
public int no_back_scroll = 0;
public int forw_prompt;
public int first_time = 1;

extern int sigs;
extern int top_scroll;
extern int quiet;
extern int sc_width, sc_height;
extern int hshift;
extern int auto_wrap;
extern int plusoption;
extern int forw_scroll;
extern int back_scroll;
extern int ignore_eoi;
extern int clear_bg;
extern int final_attr;
extern int header_lines;
extern int header_cols;
#if HILITE_SEARCH
extern int size_linebuf;
extern int hilite_search;
extern int status_col;
#endif
#if TAGS
extern char *tagoption;
#endif

/*
 * Sound the bell to indicate user is trying to move past end of file.
 */
    static void
eof_bell(VOID_PARAM)
{
#if HAVE_TIME
    static time_type last_eof_bell = 0;
    time_type now = get_time();
    if (now == last_eof_bell) /* max once per second */
        return;
    last_eof_bell = now;
#endif
    if (quiet == NOT_QUIET)
        bell();
    else
        vbell();
}

/*
 * Check to see if the end of file is currently displayed.
 */
    public int
eof_displayed(VOID_PARAM)
{
    POSITION pos;

    if (ignore_eoi)
        return (0);

    if (ch_length() == NULL_POSITION)
        /*
         * If the file length is not known,
         * we can't possibly be displaying EOF.
         */
        return (0);

    /*
     * 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);
    return (pos == NULL_POSITION || pos == ch_length());
}

/*
 * Check to see if the entire file is currently displayed.
 */
    public int
entire_file_displayed(VOID_PARAM)
{
    POSITION pos;

    /* Make sure last line of file is displayed. */
    if (!eof_displayed())
        return (0);

    /* Make sure first line of file is displayed. */
    pos = position(0);
    return (pos == NULL_POSITION || pos == 0);
}

/*
 * 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.
 */
    public void
squish_check(VOID_PARAM)
{
    if (!squished)
        return;
    squished = 0;
    repaint();
}

/*
 * Read the first pfx columns of the next line.
 * If skipeol==0 stop there, otherwise read and discard chars to end of line.
 */
    static POSITION
forw_line_pfx(pos, pfx, skipeol)
    POSITION pos;
    int pfx;
    int skipeol;
{
    int save_sc_width = sc_width;
    int save_auto_wrap = auto_wrap;
    int save_hshift = hshift;
    /* Set fake sc_width to force only pfx chars to be read. */
    sc_width = pfx + line_pfx_width();
    auto_wrap = 0;
    hshift = 0;
    pos = forw_line_seg(pos, skipeol, FALSE, FALSE);
    sc_width = save_sc_width;
    auto_wrap = save_auto_wrap;
    hshift = save_hshift;
    return pos;
}

/*
 * Set header text color.
 * Underline last line of headers, but not at beginning of file
 * (where there is no gap between the last header line and the next line).
 */
    static void
set_attr_header(ln)
    int ln;
{
    set_attr_line(AT_COLOR_HEADER);
    if (ln+1 == header_lines && position(0) != ch_zero())
        set_attr_line(AT_UNDERLINE);
}

/*
 * Display file headers, overlaying text already drawn
 * at top and left of screen.
 */
    public int
overlay_header(VOID_PARAM)
{
    POSITION pos = ch_zero(); /* header lines are at beginning of file */
    int ln;
    int moved = FALSE;

    if (header_lines > 0)
    {
        /* Draw header_lines lines from start of file at top of screen. */
        home();
        for (ln = 0; ln < header_lines; ++ln)
        {
            pos = forw_line(pos);
            set_attr_header(ln);
            clear_eol();
            put_line();
        }
        moved = TRUE;
    }
    if (header_cols > 0)
    {
        /* Draw header_cols columns at left of each line. */
        home();
        pos = ch_zero();
        for (ln = 0; ln < sc_height-1; ++ln)
        {
            if (ln >= header_lines) /* switch from header lines to normal lines */
                pos = position(ln);
            if (pos == NULL_POSITION)
                putchr('\n');
            else
            {
                /* Need skipeol for all header lines except the last one. */
                pos = forw_line_pfx(pos, header_cols, ln+1 < header_lines);
                set_attr_header(ln);
                put_line();
            }
        }
        moved = TRUE;
    }
    if (moved)
        lower_left();
    return moved;
}

/*
 * 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)
    int n;
    POSITION pos;
    int force;
    int only_last;
    int nblank;
{
    int nlines = 0;
    int do_repaint;

    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 HILITE_SEARCH
    if (hilite_search == OPT_ONPLUS || is_filtering() || status_col) {
        prep_hilite(pos, pos + 4*size_linebuf, ignore_eoi ? 1 : -1);
        pos = next_unfiltered(pos);
    }
#endif

    if (!do_repaint)
    {
        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;
            clear();
            home();
        }

        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)
            {
                clear();
                home();
            } else if (!first_time && !is_filtering())
            {
                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 HILITE_SEARCH
            pos = next_unfiltered(pos);
#endif
            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.
                 */
                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;
        }
        put_line();
#if 0
        /* {{
         * Can't call clear_eol here.  The cursor might be at end of line
         * on an ignaw terminal, so clear_eol would clear the last char
         * of the current line instead of all of the next line.
         * If we really need to do this on clear_bg terminals, we need
         * to find a better way.
         * }}
         */
        if (clear_bg && apply_at_specials(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();
        }
#endif
        forw_prompt = 1;
    }

    if (header_lines > 0)
    {
        /*
         * Don't allow ch_zero to appear on screen except at top of screen.
         * Otherwise duplicate header lines may be displayed.
         */
        if (onscreen(ch_zero()) > 0)
        {
            jump_loc(ch_zero(), 0); /* {{ yuck }} */
            return;
        }
    }
    if (nlines == 0 && !ignore_eoi)
        eof_bell();
    else if (do_repaint)
        repaint();
    else
    {
        overlay_header();
        /* lower_left(); {{ considered harmful? }} */
    }
    first_time = 0;
    (void) currline(BOTTOM);
}

/*
 * Display n lines, scrolling backward.
 */
    public void
back(n, pos, force, only_last)
    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) || header_lines > 0);
#if HILITE_SEARCH
    if (hilite_search == OPT_ONPLUS || is_filtering() || status_col) {
        prep_hilite((pos < 3*size_linebuf) ?  0 : pos - 3*size_linebuf, pos, -1);
    }
#endif
    while (--n >= 0)
    {
        /*
         * Get the previous line of input.
         */
#if HILITE_SEARCH
        pos = prev_unfiltered(pos);
#endif

        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();
        }
    }
    if (nlines == 0)
        eof_bell();
    else if (do_repaint)
        repaint();
    else
    {
        overlay_header();
        lower_left();
    }
    (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 (get_quit_at_eof() && eof_displayed() && !(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();
            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(VOID_PARAM)
{
    if (no_back_scroll)
        return (0);
    if (back_scroll >= 0)
        return (back_scroll);
    if (top_scroll)
        return (sc_height - 2);
    return (10000); /* infinity */
}

/*
 * Will the entire file fit on one screen?
 */
    public int
get_one_screen(VOID_PARAM)
{
    int nlines;
    POSITION pos = ch_zero();

    for (nlines = 0;  nlines < sc_height;  nlines++)
    {
        pos = forw_line(pos);
        if (pos == NULL_POSITION) break;
    }
    return (nlines < sc_height);
}