File: postlinebreak.w

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% postlinebreak.w
%
% Copyright 2006-2010 Taco Hoekwater <taco@@luatex.org>
%
% This file is part of LuaTeX.
%
% LuaTeX is free software; you can redistribute it and/or modify it under
% the terms of the GNU General Public License as published by the Free
% Software Foundation; either version 2 of the License, or (at your
% option) any later version.
%
% LuaTeX is distributed in the hope that it will be useful, but WITHOUT
% ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
% FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public
% License for more details.
%
% You should have received a copy of the GNU General Public License along
% with LuaTeX; if not, see <http://www.gnu.org/licenses/>.

@ @c


#include "ptexlib.h"

@ So far we have gotten a little way into the |line_break| routine, having
covered its important |try_break| subroutine. Now let's consider the
rest of the process.

The main loop of |line_break| traverses the given hlist,
starting at |vlink(temp_head)|, and calls |try_break| at each legal
breakpoint. A variable called |auto_breaking| is set to true except
within math formulas, since glue nodes are not legal breakpoints when
they appear in formulas.

The current node of interest in the hlist is pointed to by |cur_p|. Another
variable, |prev_p|, is usually one step behind |cur_p|, but the real
meaning of |prev_p| is this: If |type(cur_p)=glue_node| then |cur_p| is a legal
breakpoint if and only if |auto_breaking| is true and |prev_p| does not
point to a glue node, penalty node, explicit kern node, or math node.

@ The total number of lines that will be set by |post_line_break|
is |best_line-prev_graf-1|. The last breakpoint is specified by
|break_node(best_bet)|, and this passive node points to the other breakpoints
via the |prev_break| links. The finishing-up phase starts by linking the
relevant passive nodes in forward order, changing |prev_break| to
|next_break|. (The |next_break| fields actually reside in the same memory
space as the |prev_break| fields did, but we give them a new name because
of their new significance.) Then the lines are justified, one by one.

The |post_line_break| must also keep an dir stack, so that it can
output end direction instructions at the ends of lines
and begin direction instructions at the beginnings of lines.

@c
#define next_break prev_break   /*new name for |prev_break| after links are reversed */

/* the ints are actually halfwords */
void ext_post_line_break(int paragraph_dir,
                         int right_skip,
                         int left_skip,
                         int protrude_chars,
                         halfword par_shape_ptr,
                         int adjust_spacing,
                         halfword inter_line_penalties_ptr,
                         int inter_line_penalty,
                         int club_penalty,
                         halfword club_penalties_ptr,
                         halfword widow_penalties_ptr,
                         int widow_penalty,
                         int broken_penalty,
                         halfword final_par_glue,
                         halfword best_bet,
                         halfword last_special_line,
                         scaled second_width,
                         scaled second_indent,
                         scaled first_width,
                         scaled first_indent, halfword best_line)
{

    boolean have_directional = true;
    halfword q, r;              /* temporary registers for list manipulation */
    halfword k;
    scaled w;
    boolean glue_break;         /* was a break at glue? */
    boolean disc_break;         /*was the current break at a discretionary node? */
    boolean post_disc_break;    /*and did it have a nonempty post-break part? */
    scaled cur_width;           /*width of line number |cur_line| */
    scaled cur_indent;          /*left margin of line number |cur_line| */
    int pen;                    /*use when calculating penalties between lines */
    halfword cur_p;             /* |cur_p|, but localized */
    halfword cur_line;          /*the current line number being justified */

    dir_ptr = cur_list.dirs_field;
    /* Reverse the links of the relevant passive nodes, setting |cur_p| to
       the first breakpoint; */
    /* The job of reversing links in a list is conveniently regarded as the job
       of taking items off one stack and putting them on another. In this case we
       take them off a stack pointed to by |q| and having |prev_break| fields;
       we put them on a stack pointed to by |cur_p| and having |next_break| fields.
       Node |r| is the passive node being moved from stack to stack.
     */
    q = break_node(best_bet);
#if 0
    used_discs = used_disc(best_bet);
#endif
    /* |has_direction| */
    cur_p = null;
    do {
        r = q;
        q = prev_break(q);
        next_break(r) = cur_p;
        cur_p = r;
    } while (q != null);
    /* |cur_p| is now the first breakpoint; */

    cur_line = cur_list.pg_field + 1;   /* prevgraf+1 */

    do {
        /* Justify the line ending at breakpoint |cur_p|, and append it to the
           current vertical list, together with associated penalties and other
           insertions;    */
        /* The current line to be justified appears in a horizontal list starting
           at |vlink(temp_head)| and ending at |cur_break(cur_p)|. If |cur_break(cur_p)| is
           a glue node, we reset the glue to equal the |right_skip| glue; otherwise
           we append the |right_skip| glue at the right. If |cur_break(cur_p)| is a
           discretionary node, we modify the list so that the discretionary break
           is compulsory, and we set |disc_break| to |true|. We also append
           the |left_skip| glue at the left of the line, unless it is zero. */

#if 0
        tprint("BEGIN OF LINE ");
        print_int(cur_break(cur_p));
        breadth_max = 100000;
        depth_threshold = 100000;
        show_node_list(temp_head);
#endif

        /* DIR: Insert dir nodes at the beginning of the current line; */
        for (q = dir_ptr; q != null; q = vlink(q)) {
            halfword tmp = new_dir(dir_dir(q));
            halfword nxt = vlink(temp_head);
            delete_attribute_ref(node_attr(tmp));
            node_attr(tmp) = node_attr(temp_head);
            add_node_attr_ref(node_attr(tmp));
            couple_nodes(temp_head, tmp);
            try_couple_nodes(tmp, nxt); /* \.{\\break}\.{\\par} */
        }
        if (dir_ptr != null) {
            flush_node_list(dir_ptr);
            dir_ptr = null;
        }

        /* Modify the end of the line to reflect the nature of the break and to
           include \.{\\rightskip}; also set the proper value of |disc_break|; */
        /* At the end of the following code, |q| will point to the final node on the
           list about to be justified. In the meanwhile |r| will point to the
           node we will use to insert end-of-line stuff after. |q==null| means
           we use the final position of |r| */

        /* begin mathskip code */
        if (temp_head != null) {
                q = temp_head;
                while(q != null) {
                    if (type(q) == math_node) {
                        surround(q) = 0 ;
                        reset_glue_to_zero(q);
                        break;
                    } else if ((type(q) == hlist_node) && (subtype(q) == indent_list)) {
                        /* go on */
                    } else if (is_char_node(q)) {
                        break;
                    } else if (non_discardable(q)) {
                        break;
                    } else if (type(q) == kern_node && subtype(q) != explicit_kern && subtype(q) != italic_kern) {
                        break;
                    }
                    q = vlink(q);
                }
            }
        /* end mathskip code */

        r = cur_break(cur_p);
        q = null;
        disc_break = false;
        post_disc_break = false;
        glue_break = false;


        if (r == null) {
            for (r = temp_head; vlink(r) != null; r = vlink(r));
            if (r == final_par_glue) {
                /* This should almost always be true... */
                /* TODO assert ? */
                q = r;
                /* |q| refers to the last node of the line (and paragraph) */
                r = alink(r);
            }
            /* |r| refers to the node after which the dir nodes should be closed */
        } else if (type(r) == math_node) {
            surround(r) = 0;
            /* begin mathskip code */
            reset_glue_to_zero(r);
            /* end mathskip code */
        } else if (type(r) == glue_node) {
            copy_glue_values(r,right_skip);
            subtype(r) = right_skip_code + 1;
            glue_break = true;
            /* |q| refers to the last node of the line */
            q = r;
            r = alink(r);
            assert(vlink(r) == q);
            /* |r| refers to the node after which the dir nodes should be closed */
        } else if (type(r) == disc_node) {
            halfword a = alink(r);
            halfword v = vlink(r);
            assert(a != null);
            assert(v != null);
            switch (subtype(r)) {
            case select_disc:
                if (vlink_pre_break(r) != null) {
                    flush_node_list(vlink_pre_break(r));
                    vlink_pre_break(r) = null;
                    tlink_pre_break(r) = null;
                }
                if (vlink_no_break(r) != null) {
                    couple_nodes(a, vlink_no_break(r));
                    couple_nodes(tlink_no_break(r), r);
                    vlink_no_break(r) = null;
                    tlink_no_break(r) = null;
                }

                assert(type(a) == disc_node && subtype(a) == init_disc);
                flush_node_list(vlink_no_break(a));
                vlink_no_break(a) = null;
                tlink_no_break(a) = null;
                flush_node_list(vlink_pre_break(a));
                vlink_pre_break(a) = null;
                tlink_pre_break(a) = null;
                flush_node_list(vlink_post_break(a));
                vlink_post_break(a) = null;
                tlink_post_break(a) = null;

                break;
            case init_disc:
                assert(type(v) == disc_node && subtype(v) == select_disc);
                subtype(v) = syllable_disc;     /* not special any more */
                flush_node_list(vlink_no_break(v));
                vlink_no_break(v) = vlink_post_break(r);
                tlink_no_break(v) = tlink_post_break(r);
                vlink_post_break(r) = null;
                tlink_post_break(r) = null;
            default:
                if (vlink_no_break(r) != null) {
                    flush_node_list(vlink_no_break(r));
                    vlink_no_break(r) = null;
                    tlink_no_break(r) = null;
                }
                if (vlink_pre_break(r) != null) {
                    couple_nodes(a, vlink_pre_break(r));
                    couple_nodes(tlink_pre_break(r), r);
                    vlink_pre_break(r) = null;
                    tlink_pre_break(r) = null;
                }
            }
            if (vlink_post_break(r) != null) {
                couple_nodes(r, vlink_post_break(r));
                couple_nodes(tlink_post_break(r), v);
                vlink_post_break(r) = null;
                tlink_post_break(r) = null;
                post_disc_break = true;
            }
            disc_break = true;
        } else if (type(r) == kern_node) {
            width(r) = 0;
        }

        /* DIR: Adjust the dir stack based on dir nodes in this line; */
        /* TODO what about the previousparagraph ??? */
        if (have_directional) {
            halfword e;
            halfword p;
            for (e = vlink(temp_head); e != null && e != cur_break(cur_p); e = vlink(e)) {
                if (type(e) == dir_node) {
                    if (dir_dir(e) >= 0) {
                        dir_ptr = do_push_dir_node(dir_ptr, e);
                    } else if (dir_ptr != null && dir_dir(dir_ptr) == (dir_dir(e) + dir_swap)) {
                        dir_ptr = do_pop_dir_node(dir_ptr);
                    }
                }
            }
            assert(e == cur_break(cur_p));

            /* DIR: Insert dir nodes at the end of the current line; */
            e = vlink(r);
            for (p = dir_ptr; p != null; p = vlink(p)) {
                halfword s = new_dir(dir_dir(p) - dir_swap);
                delete_attribute_ref(node_attr(s));
                node_attr(s) = node_attr(r);
                add_node_attr_ref(node_attr(s));
                couple_nodes(r, s);
                try_couple_nodes(s, e);
                r = s;
            }
        }
        if (passive_right_box(cur_p) != null) {
            /* TODO: CHECK has |s| below a |alink| ? */
            halfword s = copy_node_list(passive_right_box(cur_p));
            halfword e = vlink(r);
            couple_nodes(r, s);
            try_couple_nodes(s, e);
            r = s;
        }
        if (q == null) {
            q = r;
        }
        /* Now [q] refers to the last node on the line */

        /* FIXME from this point on we no longer keep alink() valid */

        /* at this point |q| is the rightmost breakpoint; the only exception is
           the case of a discretionary break with non-empty |pre_break|, then |q|
           has been changed to the last node of the |pre_break| list */
        /* If the par ends with a \break command, the last line is utterly empty.
           That is the case of |q==temp_head| */
        if (q != temp_head && protrude_chars > 0) {
            halfword p, ptmp;
            if (disc_break && (is_char_node(q) || (type(q) != disc_node))) {
                p = q;          /* |q| has been reset to the last node of |pre_break| */
                ptmp = p;
            } else {
                p = alink(q);   /* get |vlink(p) = q| */
                assert(vlink(p) == q);
                ptmp = p;
            }
            p = find_protchar_right(vlink(temp_head), p);
            w = char_pw(p, right_side);
            if (w != 0) {       /* we have found a marginal kern, append it after |ptmp| */
                k = new_margin_kern(-w, last_rightmost_char, right_side);
                delete_attribute_ref(node_attr(k));
                node_attr(k) = node_attr(p);
                add_node_attr_ref(node_attr(k));
                try_couple_nodes(k, vlink(ptmp));
                couple_nodes(ptmp,k);
                if (ptmp == q)
                    q = vlink(q);
            }
        }
        /* if |q| was not a breakpoint at glue and has been reset to |rightskip|
           then we append |rightskip| after |q| now */
        if (!glue_break) {
            /* Put the \.{\\rightskip} glue after node |q|; */
            halfword r1 = new_glue((right_skip == null ? zero_glue : right_skip));
            subtype(r1) = right_skip_code+1;
            try_couple_nodes(r1,vlink(q));
            delete_attribute_ref(node_attr(r1));
            node_attr(r1) = node_attr(q);
            add_node_attr_ref(node_attr(r1));
            couple_nodes(q,r1);
            q = r1;
        }

        /* /Modify the end of the line to reflect the nature of the break and to
           include \.{\\rightskip}; also set the proper value of |disc_break|; */

        /* Put the \.{\\leftskip} glue at the left and detach this line; */
        /* The following code begins with |q| at the end of the list to be
           justified. It ends with |q| at the beginning of that list, and with
           |vlink(temp_head)| pointing to the remainder of the paragraph, if any. */
        r = vlink(q);
        vlink(q) = null;

        q = vlink(temp_head);
        try_couple_nodes(temp_head, r);
        if (passive_left_box(cur_p) != null && passive_left_box(cur_p) != 0) {
            /* omega bits: */
            halfword s;
            r = copy_node_list(passive_left_box(cur_p));
            s = vlink(q);
            couple_nodes(r,q);
            q = r;
            if ((cur_line == cur_list.pg_field + 1) && (s != null)) {
                if (type(s) == hlist_node) {
                    if (list_ptr(s) == null) {
                        q = vlink(q);
                        try_couple_nodes(r,vlink(s));
                        try_couple_nodes(s, r);
                    }
                }
            }
        }
        /*at this point |q| is the leftmost node; all discardable nodes have been discarded */
        if (protrude_chars > 0) {
            halfword p;
            p = q;
            p = find_protchar_left(p, false);   /* no more discardables */
            w = char_pw(p, left_side);
            if (w != 0) {
                k = new_margin_kern(-w, last_leftmost_char, left_side);
                delete_attribute_ref(node_attr(k));
                node_attr(k) = node_attr(q);
                add_node_attr_ref(node_attr(k));
                couple_nodes(k,q);
                q = k;
            }
        }
        if (! glue_is_zero(left_skip)) {
            r = new_glue(left_skip);
            subtype(r) = left_skip_code+1;
            delete_attribute_ref(node_attr(r));
            node_attr(r) = node_attr(q);
            add_node_attr_ref(node_attr(r));
            couple_nodes(r,q);
            q = r;
        }
        /* /Put the \.{\\leftskip} glue at the left and detach this line; */

        /* Call the packaging subroutine, setting |just_box| to the justified box; */
        /* Now |q| points to the hlist that represents the current line of the
           paragraph. We need to compute the appropriate line width, pack the
           line into a box of this size, and shift the box by the appropriate
           amount of indentation. */
        if (cur_line > last_special_line) {
            cur_width = second_width;
            cur_indent = second_indent;
        } else if (par_shape_ptr == null) {
            cur_width = first_width;
            cur_indent = first_indent;
        } else {
            cur_indent = varmem[(par_shape_ptr + 2 * cur_line)].cint;
            cur_width = varmem[(par_shape_ptr + 2 * cur_line + 1)].cint;
        }
        adjust_tail = adjust_head;
        pre_adjust_tail = pre_adjust_head;
        if (adjust_spacing > 0) {
            just_box = hpack(q, cur_width, cal_expand_ratio, paragraph_dir);
        } else {
            just_box = hpack(q, cur_width, exactly, paragraph_dir);
        }
        shift_amount(just_box) = cur_indent;
        subtype(just_box) = line_list;
        /* /Call the packaging subroutine, setting |just_box| to the justified box; */

        if ((vlink(contrib_head) != null))
            checked_break_filter(pre_box);
        if (pre_adjust_head != pre_adjust_tail) {
            append_list(pre_adjust_head, pre_adjust_tail);
            checked_break_filter(pre_adjust);
        }
        pre_adjust_tail = null;
        append_to_vlist(just_box,lua_key_index(post_linebreak));
        checked_break_filter(box);
        if (adjust_head != adjust_tail) {
            append_list(adjust_head, adjust_tail);
            checked_break_filter(adjust);
        }
        adjust_tail = null;

        /* /Append the new box to the current vertical list, followed by the list of
           special nodes taken out of the box by the packager; */

        /* Append a penalty node, if a nonzero penalty is appropriate */
        /* Penalties between the lines of a paragraph come from club and widow lines,
           from the |inter_line_penalty| parameter, and from lines that end at
           discretionary breaks.  Breaking between lines of a two-line paragraph gets
           both club-line and widow-line penalties. The local variable |pen| will
           be set to the sum of all relevant penalties for the current line, except
           that the final line is never penalized. */
        if (cur_line + 1 != best_line) {
            q = inter_line_penalties_ptr;
            if (q != null) {
                r = cur_line;
                if (r > penalty(q))
                    r = penalty(q);
                pen = penalty(q + r);
            } else {
                if (passive_pen_inter(cur_p) != 0) {
                    pen = passive_pen_inter(cur_p);
                } else {
                    pen = inter_line_penalty;
                }
            }
            q = club_penalties_ptr;
            if (q != null) {
                r = cur_line - cur_list.pg_field;       /* prevgraf */
                if (r > penalty(q))
                    r = penalty(q);
                pen += penalty(q + r);
            } else if (cur_line == cur_list.pg_field + 1) {     /* prevgraf */
                pen += club_penalty;
            }
            q = widow_penalties_ptr;
            if (q != null) {
                r = best_line - cur_line - 1;
                if (r > penalty(q))
                    r = penalty(q);
                pen += penalty(q + r);
            } else if (cur_line + 2 == best_line) {
                pen += widow_penalty;
            }
            if (disc_break) {
                if (passive_pen_broken(cur_p) != 0) {
                    pen += passive_pen_broken(cur_p);
                } else {
                    pen += broken_penalty;
                }
            }
            if (pen != 0) {
                r = new_penalty(pen,linebreak_penalty);
                couple_nodes(cur_list.tail_field, r);
                cur_list.tail_field = r;
            }
        }
        /* /Append a penalty node, if a nonzero penalty is appropriate */

        /* /Justify the line ending at breakpoint |cur_p|, and append it to the
           current vertical list, together with associated penalties and other
           insertions;   */
        incr(cur_line);
        cur_p = next_break(cur_p);
        if (cur_p != null && !post_disc_break) {
            /* Prune unwanted nodes at the beginning of the next line; */
            /* Glue and penalty and kern and math nodes are deleted at the
               beginning of a line, except in the anomalous case that the
               node to be deleted is actually one of the chosen
               breakpoints. Otherwise the pruning done here is designed to
               match the lookahead computation in |try_break|, where the
               |break_width| values are computed for non-discretionary
               breakpoints. */
            r = temp_head;
            /*
                Normally we have a matching math open and math close node but when we cross a line
                the open node is removed, including any glue or penalties following it. This is however
                not that nice for callbacks that rely on symmetry. Of course this only counts for one
                liners, as we can still have only a begin or end node on a line. The end_of_math lua
                helper is made robust against this although there you should be aware of the fact that
                one can end up in the middle of math in callbacks that don't work on whole paragraphs,
                but at least this branch makes sure that some proper analysis is possible. (todo: check
                if math glyphs have the subtype marked done).

                Todo: turn math nodes into glues when mathskip otherwise remove them.
            */
            while (1) {
                q = vlink(r);
                /*
                if (q == cur_break(cur_p) || is_char_node(q))
                    break;
                if (!((type(q) == local_par_node))) {
                    if (non_discardable(q) || (type(q) == kern_node && subtype(q) != explicit_kern && subtype(q) != italic_kern))
                        break;
                }
                */
                if (type(q) == math_node) {
                    /* begin mathskip code */
                    surround(q) = 0 ;
                    reset_glue_to_zero(q);
                    /* end mathskip code */
                }
                if (q == cur_break(cur_p)) {
                    break;
                } else if (is_char_node(q)) {
                    break;
                } else if (type(q) == local_par_node) {
                    /* weird, in the middle somewhere */
                } else if (non_discardable(q)) {
                    break;
                } else if (type(q) == kern_node && subtype(q) != explicit_kern && subtype(q) != italic_kern) {
                    break;
                }
                r = q;
            }
            if (r != temp_head) {
                vlink(r) = null;
                flush_node_list(vlink(temp_head));
                try_couple_nodes(temp_head, q);
            }
        }
    } while (cur_p != null);
    if ((cur_line != best_line) || (vlink(temp_head) != null))
        confusion("line breaking");
    cur_list.pg_field = best_line - 1;  /* prevgraf */
    cur_list.dirs_field = dir_ptr;      /* |dir_save| */
    dir_ptr = null;
}