How can I enlarge the thin, zero-width lines of a PDF?

[Aaron]

Q:

Some documents, such as CAD files, can have lots of very thin lines in them. Oftentimes, this is caused by zero-width lines, which my users can find hard to see even when zoomed in. Is there any way to make lines larger, so that they're easier to read?

A:

The following C# code can be used to expand the line widths of paths, as well as characters of Type3 fonts:

//

// Copyright (c) 2001-2020 by PDFTron Systems Inc. All Rights Reserved.

//

using System;

using System.Collections.Generic;

using pdftron;

using pdftron.Common;

using pdftron.Filters;

using pdftron.SDF;

using pdftron.PDF;

using XSet = System.Collections.Generic.List<int>;

using EltCase = System.Action<pdftron.PDF.ElementReader, pdftron.PDF.ElementWriter, pdftron.PDF.Element>;

namespace ElementEditTestCS

{

  class Class1

  {

    private static pdftron.PDFNetLoader pdfNetLoader = pdftron.PDFNetLoader.Instance();

    static Class1() {}

    static void ProcessElements(ElementReader reader, ElementWriter writer, XSet visited, 

                                EltCase path, EltCase text, EltCase form)

    {

      Element element;

      while ((element = reader.Next()) != null)

      {

        switch (element.GetType())

        {

          case Element.Type.e_path:

            path(reader, writer, element);

            break;

          case Element.Type.e_text:

            text(reader, writer, element);

            break;

          case Element.Type.e_form:

            {

              writer.WriteElement(element);

              Obj form_obj = element.GetXObject();

              if (!visited.Contains(form_obj.GetObjNum()))

              {

                visited.Add(form_obj.GetObjNum());

                ElementWriter new_writer = new ElementWriter();

                reader.FormBegin();

                new_writer.Begin(form_obj, true);

                reader.ClearChangeList();

                new_writer.SetDefaultGState(reader);

                form(reader, writer, element);

                new_writer.End();

                reader.End();

              }

              break;

            }

          default:

            writer.WriteElement(element);

            break;

        }

      }

    }

    static EltCase EnlargeZeroWidthLines(int new_width)

    {

      return (reader, writer, element) =>

        {

          GState gs = element.GetGState();

          if (gs.GetLineWidth() < 0.001) gs.SetLineWidth(new_width);

          writer.WriteElement(element);

        };

    }

    static void EnlargeCharacters(ElementReader reader_, ElementWriter writer_, XSet visited_)

    {

      ProcessElements(reader_, writer_, visited_, 

        EnlargeZeroWidthLines(10), // make zero-width lines in characters 10 units wide (better appearance)

        (reader, writer, element) => { writer.WriteElement(element); },

        (reader, writer, element) => { EnlargeCharacters(reader, writer, visited_); });

    }

    static void RewriteCharacters(PDFDoc doc, XSet charprocs)

    {

      ElementWriter writer = new ElementWriter();

      ElementReader reader = new ElementReader();

      XSet visited = new XSet();

      foreach (int charproc in charprocs)

      {

        SDFDoc sdf = doc.GetSDFDoc();

        reader.Begin(sdf.GetObj(charproc));

        writer.Begin(sdf);

        EnlargeCharacters(reader, writer, visited);

        reader.End();

        sdf.Swap(charproc, writer.End().GetObjNum());

      }

    }

    static XSet EnlargePaths(ElementReader reader_, ElementWriter writer_, XSet visited_)

    {

      XSet charprocs = new XSet();

      ProcessElements(reader_, writer_, visited_, 

        EnlargeZeroWidthLines(1), // make zero-width paths one unit wide

        (reader, writer, element) =>

          {

            writer.WriteElement(element);

            Obj font_dict = element.GetGState().GetFont().GetSDFObj();

            if (font_dict.Get("Subtype").Value().GetName() != "Type3") return;

            DictIterator itr = font_dict.Get("CharProcs").Value().GetDictIterator();

            while (itr.HasNext())

            {

              int n = itr.Value().GetObjNum();

              if (!charprocs.Contains(n)) charprocs.Add(n);

              itr.Next();

            }

          },

        (reader, writer, element) => { charprocs.AddRange(EnlargePaths(reader, writer, visited_)); });

      return charprocs;

    }

    static XSet RewritePages(PDFDoc doc)

    {

      ElementWriter writer = new ElementWriter();

      ElementReader reader = new ElementReader();

      XSet visited = new XSet();

      XSet charprocs = new XSet();

      PageIterator itr = doc.GetPageIterator();

      while (itr.HasNext())

      {

        Page page = itr.Current();

        visited.Add(page.GetSDFObj().GetObjNum());

        reader.Begin(page);

        writer.Begin(page, ElementWriter.WriteMode.e_replacement, false, true, page.GetResourceDict());

        charprocs.AddRange(EnlargePaths(reader, writer, visited));

        writer.End();

        reader.End();

        itr.Next();

      }

      return charprocs; // all type3 font characters (each might contain zero-width lines)

    }

    [STAThread]

    static void Main(string[] args)

    {

      PDFNet.Initialize();

      string input_path = "../../TestFiles/";

      string output_path = "../../TestFiles/Output/";

      string input_filename = //.....

      string output_filename = //.....

      try

      {

        Console.WriteLine("Opening the input file...");

        using (PDFDoc doc = new PDFDoc(input_path + input_filename))

        {

          doc.InitSecurityHandler();

          XSet charprocs = RewritePages(doc);

          RewriteCharacters(doc, charprocs);

          doc.Save(output_path + output_filename, SDFDoc.SaveOptions.e_remove_unused);

          Console.WriteLine("Done. Result saved in {0}...", output_filename);

        }

      }

      catch (PDFNetException e)

      {

        Console.WriteLine(e.Message);

      }

    }

  }

}