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bk_pdf.c

/*
 * PDF backend for Halibut
 */

#include <assert.h>
#include "halibut.h"
#include "paper.h"

#define TREE_BRANCH 2                /* max branching factor in page tree */

paragraph *pdf_config_filename(char *filename)
{
    return cmdline_cfg_simple("pdf-filename", filename, NULL);
}

typedef struct object_Tag object;
typedef struct objlist_Tag objlist;

00019 struct object_Tag {
    objlist *list;
    object *next;
    int number;
    rdstringc main, stream;
    int size, fileoff;
    char *final;
};

00028 struct objlist_Tag {
    int number;
    object *head, *tail;
};

static object *new_object(objlist *list);
static void objtext(object *o, char const *text);
static void objstream(object *o, char const *text);
static void pdf_string(void (*add)(object *, char const *),
                   object *, char const *);
static void pdf_string_len(void (*add)(object *, char const *),
                     object *, char const *, int);
static void objref(object *o, object *dest);

static void make_pages_node(object *node, object *parent, page_data *first,
                      page_data *last, object *resources);
static int make_outline(object *parent, outline_element *start, int n,
                  int open);
static int pdf_versionid(FILE *fp, word *words);

void pdf_backend(paragraph *sourceform, keywordlist *keywords,
             indexdata *idx, void *vdoc) {
    document *doc = (document *)vdoc;
    int font_index;
    font_encoding *fe;
    page_data *page;
    int pageno;
    FILE *fp;
    char *filename;
    paragraph *p;
    objlist olist;
    object *o, *cat, *outlines, *pages, *resources;
    int fileoff;

    IGNORE(keywords);
    IGNORE(idx);

    filename = dupstr("output.pdf");
    for (p = sourceform; p; p = p->next) {
      if (p->type == para_Config) {
          if (!ustricmp(p->keyword, L"pdf-filename")) {
            sfree(filename);
            filename = dupstr(adv(p->origkeyword));
          }
      }
    }

    olist.head = olist.tail = NULL;
    olist.number = 1;

    cat = new_object(&olist);
    if (doc->n_outline_elements > 0)
      outlines = new_object(&olist);
    else
      outlines = NULL;
    pages = new_object(&olist);
    resources = new_object(&olist);

    /*
     * The catalogue just contains references to the outlines and
     * pages objects.
     */
    objtext(cat, "<<\n/Type /Catalog");
    if (outlines) {
      objtext(cat, "\n/Outlines ");
      objref(cat, outlines);
    }
    objtext(cat, "\n/Pages ");
    objref(cat, pages);
    if (outlines)
      objtext(cat, "\n/PageMode /UseOutlines");
    objtext(cat, "\n>>\n");

    /*
     * Set up the resources dictionary, which mostly means
     * providing all the font objects and names to call them by.
     */
    font_index = 0;
    objtext(resources, "<<\n/Font <<\n");
    for (fe = doc->fonts->head; fe; fe = fe->next) {
      char fname[40];
      int i;
      object *font;

      sprintf(fname, "f%d", font_index++);
      fe->name = dupstr(fname);

      font = new_object(&olist);

      objtext(resources, "/");
      objtext(resources, fe->name);
      objtext(resources, " ");
      objref(resources, font);
      objtext(resources, "\n");

      objtext(font, "<<\n/Type /Font\n/Subtype /Type1\n/Name /");
      objtext(font, fe->name);
      objtext(font, "\n/BaseFont /");
      objtext(font, fe->font->name);
      objtext(font, "\n/Encoding <<\n/Type /Encoding\n/Differences [");

      for (i = 0; i < 256; i++) {
          char buf[20];
          if (!fe->vector[i])
            continue;
          sprintf(buf, "\n%d /", i);
          objtext(font, buf);
          objtext(font, fe->vector[i] ? fe->vector[i] : ".notdef");
      }

      objtext(font, "\n]\n>>\n");

      {
          object *widths = new_object(&olist);
          objtext(font, "/FirstChar 0\n/LastChar 255\n/Widths ");
          objref(font, widths);
          objtext(font, "\n");
          objtext(widths, "[\n");
          for (i = 0; i < 256; i++) {
            char buf[80];
            double width;
            if (fe->indices[i] < 0)
                width = 0.0;
            else
                width = fe->font->widths[fe->indices[i]];
            sprintf(buf, "%g\n", 1000.0 * width / FUNITS_PER_PT);
            objtext(widths, buf);
          }
          objtext(widths, "]\n");
      }

      objtext(font, ">>\n");
    }
    objtext(resources, ">>\n>>\n");

    /*
     * Define the page objects for each page, and get each one
     * ready to have a `Parent' specification added to it.
     */
    for (page = doc->pages; page; page = page->next) {
      object *opage;

      opage = new_object(&olist);
      page->spare = opage;
      objtext(opage, "<<\n/Type /Page\n");
    }

    /*
     * Recursively build the page tree.
     */
    make_pages_node(pages, NULL, doc->pages, NULL, resources);

    /*
     * Create and render the individual pages.
     */
    pageno = 0;
    for (page = doc->pages; page; page = page->next) {
      object *opage, *cstr;
      rect *r;
      text_fragment *frag, *frag_end;
      char buf[256];
      int x, y, lx, ly;

      opage = (object *)page->spare;
      /*
       * At this point the page dictionary is already
       * half-written, with /Type and /Parent already present. We
       * continue from there.
       */

      /*
       * The PDF spec says /Resources is required, but also says
       * that it's inheritable and may be omitted if it's present
       * in a Pages node. In our case it is: it's present in the
       * topmost /Pages node because we carefully put it there.
       * So we don't need a /Resources entry here.
       */
      sprintf(buf, "/MediaBox [0 0 %g %g]\n",
            doc->paper_width / FUNITS_PER_PT,
            doc->paper_height / FUNITS_PER_PT);
      objtext(opage, buf);

      /*
       * Now we're ready to define a content stream containing
       * the actual text on the page.
       */
      cstr = new_object(&olist);
      objtext(opage, "/Contents ");
      objref(opage, cstr);
      objtext(opage, "\n");

      /*
       * Render any rectangles on the page.
       */
      for (r = page->first_rect; r; r = r->next) {
          char buf[512];
          sprintf(buf, "%g %g %g %g re f\n",
                r->x / FUNITS_PER_PT, r->y / FUNITS_PER_PT,
                r->w / FUNITS_PER_PT, r->h / FUNITS_PER_PT);
          objstream(cstr, buf);
      }

      objstream(cstr, "BT\n");

      /*
       * PDF tracks two separate current positions: the position
       * given in the `line matrix' and the position given in the
       * `text matrix'. We must therefore track both as well.
       * They start off at -1 (unset).
       */
      lx = ly = -1;
      x = y = -1;

      frag = page->first_text;
      while (frag) {
          /*
           * For compactness, I'm going to group text fragments
           * into subsequences that use the same font+size. So
           * first find the end of this subsequence.
           */
          for (frag_end = frag;
             (frag_end &&
              frag_end->fe == frag->fe &&
              frag_end->fontsize == frag->fontsize);
             frag_end = frag_end->next);

          /*
           * Now select the text fragment, and prepare to display
           * the text.
           */
          objstream(cstr, "/");
          objstream(cstr, frag->fe->name);
          sprintf(buf, " %d Tf ", frag->fontsize);
          objstream(cstr, buf);

          while (frag && frag != frag_end) {
            /*
             * Place the text position for the first piece of
             * text.
             */
            if (lx < 0) {
                sprintf(buf, "1 0 0 1 %g %g Tm ",
                      frag->x/FUNITS_PER_PT, frag->y/FUNITS_PER_PT);
            } else {
                sprintf(buf, "%g %g Td ",
                      (frag->x - lx)/FUNITS_PER_PT,
                      (frag->y - ly)/FUNITS_PER_PT);
            }
            objstream(cstr, buf);
            lx = x = frag->x;
            ly = y = frag->y;

            /*
             * See if we're going to use Tj (show a single
             * string) or TJ (show an array of strings with
             * x-spacings between them). We determine this by
             * seeing if there's more than one text fragment in
             * sequence with the same y-coordinate.
             */
            if (frag->next && frag->next != frag_end &&
                frag->next->y == y) {
                /*
                 * The TJ strategy.
                 */
                objstream(cstr, "[");
                while (frag && frag != frag_end && frag->y == y) {
                  if (frag->x != x) {
                      sprintf(buf, "%g",
                            (x - frag->x) * 1000.0 /
                            (FUNITS_PER_PT * frag->fontsize));
                      objstream(cstr, buf);
                  }
                  pdf_string(objstream, cstr, frag->text);
                  x = frag->x + frag->width;
                  frag = frag->next;
                }
                objstream(cstr, "]TJ\n");
            } else
            {
                /*
                 * The Tj strategy.
                 */
                pdf_string(objstream, cstr, frag->text);
                objstream(cstr, "Tj\n");
                frag = frag->next;
            }
          }
      }
      objstream(cstr, "ET");

      /*
       * Also, we want an annotation dictionary containing the
       * cross-references from this page.
       */
      if (page->first_xref) {
          xref *xr;
          objtext(opage, "/Annots [\n");

          for (xr = page->first_xref; xr; xr = xr->next) {
            object *annot;
            char buf[256];

            annot = new_object(&olist);
            objref(opage, annot);
            objtext(opage, "\n");

            objtext(annot, "<<\n/Type /Annot\n/Subtype /Link\n/Rect [");
            sprintf(buf, "%g %g %g %g",
                  xr->lx / FUNITS_PER_PT, xr->by / FUNITS_PER_PT,
                  xr->rx / FUNITS_PER_PT, xr->ty / FUNITS_PER_PT);
            objtext(annot, buf);
            objtext(annot, "]\n/Border [0 0 0]\n");

            if (xr->dest.type == PAGE) {
                objtext(annot, "/Dest [");
                objref(annot, (object *)xr->dest.page->spare);
                objtext(annot, " /XYZ null null null]\n");
            } else {
                objtext(annot, "/A <<\n/Type /Action\n/S /URI\n/URI ");
                pdf_string(objtext, annot, xr->dest.url);
                objtext(annot, "\n>>\n");
            }

            objtext(annot, ">>\n");
          }

          objtext(opage, "]\n");
      }

      objtext(opage, ">>\n");
    }

    /*
     * Set up the outlines dictionary.
     */
    if (outlines) {
      int topcount;
      char buf[80];

      objtext(outlines, "<<\n/Type /Outlines\n");
      topcount = make_outline(outlines, doc->outline_elements,
                        doc->n_outline_elements, TRUE);
      sprintf(buf, "/Count %d\n>>\n", topcount);
      objtext(outlines, buf);
    }

    /*
     * Assemble the final linear form of every object.
     */
    for (o = olist.head; o; o = o->next) {
      rdstringc rs = {0, 0, NULL};
      char text[80];

      sprintf(text, "%d 0 obj\n", o->number);
      rdaddsc(&rs, text);

      if (!o->main.text && o->stream.text) {
          sprintf(text, "<<\n/Length %d\n>>\n", o->stream.pos);
          rdaddsc(&o->main, text);
      }

      assert(o->main.text);
      rdaddsc(&rs, o->main.text);
      sfree(o->main.text);

      if (rs.text[rs.pos-1] != '\n')
          rdaddc(&rs, '\n');

      if (o->stream.text) {
          /*
           * FIXME: If we ever start compressing stream data then
           * it will have zero bytes in it, so we'll have to be
           * more careful than this.
           */
          rdaddsc(&rs, "stream\n");
          rdaddsc(&rs, o->stream.text);
          rdaddsc(&rs, "\nendstream\n");
          sfree(o->stream.text);
      }

      rdaddsc(&rs, "endobj\n");

      o->final = rs.text;
      o->size = rs.pos;
    }

    /*
     * Write out the PDF file.
     */

    fp = fopen(filename, "wb");
    if (!fp) {
      error(err_cantopenw, filename);
      return;
    }

    /*
     * Header. I'm going to put the version IDs in the header as
     * well, simply in PDF comments.
     */
    fileoff = fprintf(fp, "%%PDF-1.3\n");
    for (p = sourceform; p; p = p->next)
      if (p->type == para_VersionID)
          fileoff += pdf_versionid(fp, p->words);

    /*
     * Body
     */
    for (o = olist.head; o; o = o->next) {
      o->fileoff = fileoff;
      fwrite(o->final, 1, o->size, fp);
      fileoff += o->size;
    }

    /*
     * Cross-reference table
     */
    fprintf(fp, "xref\n");
    assert(olist.head->number == 1);
    fprintf(fp, "0 %d\n", olist.tail->number + 1);
    fprintf(fp, "0000000000 65535 f \n");
    for (o = olist.head; o; o = o->next) {
      char entry[40];
      sprintf(entry, "%010d 00000 n \n", o->fileoff);
      assert(strlen(entry) == 20);
      fputs(entry, fp);
    }

    /*
     * Trailer
     */
    fprintf(fp, "trailer\n<<\n/Size %d\n/Root %d 0 R\n>>\n",
          olist.tail->number + 1, cat->number);
    fprintf(fp, "startxref\n%d\n%%%%EOF\n", fileoff);

    fclose(fp);

    sfree(filename);
}

static object *new_object(objlist *list)
{
    object *obj = snew(object);

    obj->list = list;

    obj->main.text = NULL;
    obj->main.pos = obj->main.size = 0;
    obj->stream.text = NULL;
    obj->stream.pos = obj->stream.size = 0;

    obj->number = list->number++;

    obj->next = NULL;
    if (list->tail)
      list->tail->next = obj;
    else
      list->head = obj;
    list->tail = obj;

    obj->size = 0;
    obj->final = NULL;

    return obj;
}

static void objtext(object *o, char const *text)
{
    rdaddsc(&o->main, text);
}

static void objstream(object *o, char const *text)
{
    rdaddsc(&o->stream, text);
}

static void objref(object *o, object *dest)
{
    char buf[40];
    sprintf(buf, "%d 0 R", dest->number);
    rdaddsc(&o->main, buf);
}

static void make_pages_node(object *node, object *parent, page_data *first,
                      page_data *last, object *resources)
{
    int count;
    page_data *page;
    char buf[80];

    objtext(node, "<<\n/Type /Pages\n");
    if (parent) {
      objtext(node, "/Parent ");
      objref(node, parent);
      objtext(node, "\n");
    }

    /*
     * Count the pages in this stretch, to see if there are few
     * enough to reference directly.
     */
    count = 0;
    for (page = first; page; page = page->next) {
      count++;
      if (page == last)
          break;
    }

    sprintf(buf, "/Count %d\n/Kids [\n", count);
    objtext(node, buf);

    if (count > TREE_BRANCH) {
      int i;
      page_data *thisfirst, *thislast;

      page = first;

      for (i = 0; i < TREE_BRANCH; i++) {
          int number = (i+1) * count / TREE_BRANCH - i * count / TREE_BRANCH;
          thisfirst = page;
          while (number--) {
            thislast = page;
            page = page->next;
          }

          if (thisfirst == thislast) {
            objref(node, (object *)thisfirst->spare);
            objtext((object *)thisfirst->spare, "/Parent ");
            objref((object *)thisfirst->spare, node);
            objtext((object *)thisfirst->spare, "\n");
          } else {
            object *newnode = new_object(node->list);
            make_pages_node(newnode, node, thisfirst, thislast, NULL);
            objref(node, newnode);
          }
          objtext(node, "\n");
      }

      assert(thislast == last || page == NULL);

    } else {
      for (page = first; page; page = page->next) {
          objref(node, (object *)page->spare);
          objtext(node, "\n");
          objtext((object *)page->spare, "/Parent ");
          objref((object *)page->spare, node);
          objtext((object *)page->spare, "\n");
          if (page == last)
            break;
      }
    }

    objtext(node, "]\n");

    if (resources) {
      objtext(node, "/Resources ");
      objref(node, resources);
      objtext(node, "\n");
    }

    objtext(node, ">>\n");
}

/*
 * In text on the page, PDF uses the PostScript font model, which
 * means that glyphs are identified by PS strings and hence font
 * encoding can be managed independently of the supplied encoding
 * of the font. However, in the document outline, the PDF spec
 * encodes in either PDFDocEncoding (a custom superset of
 * ISO-8859-1) or UTF-16BE.
 */
static char *pdf_outline_convert(wchar_t *s, int *len) {
    char *ret;

    ret = utoa_careful_dup(s, CS_PDF);

    /*
     * Very silly special case: if the returned string begins with
     * FE FF, then the PDF reader will mistake it for a UTF-16BE
     * string. So in this case we give up on PDFDocEncoding and
     * encode it in UTF-16 straight away.
     */
    if (ret && ret[0] == '\xFE' && ret[1] == '\xFF') {
      sfree(ret);
      ret = NULL;
    }

    if (!ret) {
      ret = utoa_dup_len(s, CS_UTF16BE, len);
    } else {
      *len = strlen(ret);
    }

    return ret;
}

static int make_outline(object *parent, outline_element *items, int n,
                  int open)
{
    int level, totalcount = 0;
    outline_element *itemp;
    object *curr, *prev = NULL, *first = NULL, *last = NULL;

    assert(n > 0);

    level = items->level;

    while (n > 0) {
      char *title;
      int titlelen;

      /*
       * Here we expect to be sitting on an item at the given
       * level. So we start by constructing an outline entry for
       * that item.
       */
      assert(items->level == level);

      title = pdf_outline_convert(items->pdata->outline_title, &titlelen);

      totalcount++;
      curr = new_object(parent->list);
      if (!first) first = curr;
      last = curr;
      objtext(curr, "<<\n/Title ");
      pdf_string_len(objtext, curr, title, titlelen);
      objtext(curr, "\n/Parent ");
      objref(curr, parent);
      objtext(curr, "\n/Dest [");
      objref(curr, (object *)items->pdata->first->page->spare);
      objtext(curr, " /XYZ null null null]\n");
      if (prev) {
          objtext(curr, "/Prev ");
          objref(curr, prev);
          objtext(curr, "\n");

          objtext(prev, "/Next ");
          objref(prev, curr);
          objtext(prev, "\n>>\n");
      }
      prev = curr;

      items++, n--;
      for (itemp = items; itemp < items+n && itemp->level > level;
           itemp++);

      if (itemp > items) {
          char buf[80];
          int count = make_outline(curr, items, itemp - items, FALSE);
          if (!open)
            count = -count;
          else
            totalcount += count;
          sprintf(buf, "/Count %d\n", count);
          objtext(curr, buf);
      }

      n -= itemp - items;
      items = itemp;
    }
    objtext(prev, ">>\n");

    assert(first && last);
    objtext(parent, "/First ");
    objref(parent, first);
    objtext(parent, "\n/Last ");
    objref(parent, last);
    objtext(parent, "\n");

    return totalcount;
}

static int pdf_versionid(FILE *fp, word *words)
{
    int ret;

    ret = fprintf(fp, "%% ");

    for (; words; words = words->next) {
      char *text;
      int type;

      switch (words->type) {
        case word_HyperLink:
        case word_HyperEnd:
        case word_UpperXref:
        case word_LowerXref:
        case word_XrefEnd:
        case word_IndexRef:
          continue;
      }

      type = removeattr(words->type);

      switch (type) {
        case word_Normal:
          text = utoa_dup(words->text, CS_ASCII);
          break;
        case word_WhiteSpace:
          text = dupstr(" ");
          break;
        case word_Quote:
          text = dupstr("'");
          break;
      }

      fputs(text, fp);
      ret += strlen(text);
      sfree(text);
    }

    ret += fprintf(fp, "\n");

    return ret;
}

static void pdf_string_len(void (*add)(object *, char const *),
                     object *o, char const *str, int len)
{
    char const *p;

    add(o, "(");
    for (p = str; len > 0; p++, len--) {
      char c[10];
      if (*p < ' ' || *p > '~') {
          sprintf(c, "\\%03o", 0xFF & (int)*p);
      } else {
          int n = 0;
          if (*p == '\\' || *p == '(' || *p == ')')
            c[n++] = '\\';
          c[n++] = *p;
          c[n] = '\0';
      }
      add(o, c);
    }
    add(o, ")");
}

static void pdf_string(void (*add)(object *, char const *),
                   object *o, char const *str)
{
    pdf_string_len(add, o, str, strlen(str));
}

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