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    {
    Derek Powles <derek.powles@eng.ox.ac.uk>

    Subject: Re Help File format

    Expanded information on Help File sources.
       In an earlier message I referred to four authors For the book in (1)
    below - my mistake - there are three.
        Derek

    (1) 'A Programmer's Guide to Turbo Vision' by Ertl, Machholz and Golgath,
    authored by the Pascal product management team at Borland in Germany.
    Pub. Addison-Wesley, ISBN 0-201-62401-X.
    The book contains chapter 12 ( 18 pages ) describing how to add a
    conText sensitive help Unit to your own TV Program.
    The use of TVHC is described ( 2 pages ). TVHC generates helptxt.pas and
    helptxt.hlp Files from a special helptxt.txt File. The .pas File is
    included in your main routine as a Unit. The HelpFile Unit is also needed,
    this Unit, TVHC and a working example are in the TVDEMO subdirectory.
    This .hlp File is not compatible With the Borland supplied Dos help Files,
    these have a name of the form *.t*h. I believe I am correct in stating that,
    other than demohelp.hlp, all supplied *.hlp Files are For Windows use.

    (2) The 'Borland Open Architecture Handbook For Pascal' describes and
    supplies the Program HL.EXE. Chapter 8 tells you '...how to create, build,
    and maintain Borland Dos Help Files'. I have attached information gleaned
    from this book.
    There are two sections, the first is information taken from the book and
    the second is a Unit holding data structures.

    look For the *****cut here*****.

    ******************cut here*********************
    {  See `Borland Open Architecture Handbook For Pascal' pages 170-177 }
    (***************************************************************
    Binary help File format -

    Records are grouped in four sections

     1 - File stamp
     2 - File signature
     3 - File version
     4 - Record Headers
       a - File header Record
       b - conText
       c - Text
       d - keyWord
       e - index
       f - compression Record
       g - indextags {= subheadings, = qualifiers}

       ***************************************************************

     1 - A File stamp is a null terminated String, note case,
          `TURBO PASCAL HelpFile.\0' or
          `TURBO C Help File.\0'  identifying the File in readable form.
          The null Character is followed by a Dos end-of-File Charcater $1A.
          This is defined as ;STAMP in the help source File.

     2 - The File signature For Borland products is a null terminated
          String `$*$* &&&&$*$' (no quotes in help Files).
          This is defined as ;SIGNATURE in the help source File.

     3 - The File version is a Record of two Bytes that define the version
          of help format and the help File Text respectively,

          Type
            TPVersionRec    = Record
              Formatversion : Byte;
              TextVersion   : Byte   {defined With ;VERSION}
              { this is For info only }
            end;
          FormatVersion For BP7     = $34
                            TP6     = $33
                            TP5     = $04
                            TP4     = $02
                            TC++3.0 = $04

     4 - Record Headers -
      All the remaining Records have a common format that includes a header
      identifying the Record's Type and length.

        Type
          TPrecHdr  = Record;
            RecType   : Byte;
            RecLength : Word;
          end;

      Field RecType is a code that identifies the Record Type.
        Type
          RecType =
            (RT_FileHeader,    {0}
             RT_ConText,       {1}
             RT_Text,          {2}
             RT_KeyWord,       {3}
             RT_Index,         {4}
             RT_Compression);  {5}
             RT_IndexTags,     {6 - only in FormatVersion $34}

      Field RecLength gives the length of the contents of the Record in
      Bytes, not including the Record header. The contents begin With the
      first Byte following the header.

      The field `RecType' Types are explained in the following Text.

      Although this structure allows an arbitrary order of Records, existing
      Borland products assume a fixed Record ordering as follows:-
            File header Record
            compression Record
            conText table
            index table
            indextags Record {introduced in BP7}
            Text Record
            keyWord Record

     4.a The File header Record defines Various parameters and options
      common to the help File.

      Type
        TPFileHdrRec     = Record
          Options        : Word;
          MainIndexScreen: Word;
          Maxscreen size : Word;
          Height         : Byte;
          Width          : Byte;
          LeftMargin     : Byte;
        end;

          Options - is a bitmapped field. Only one option currently
                    supported.
                    OF_CaseSense ($0004) (C only, not Pascal)
                      if set, index tokens are listed in mixed case
                      in the Index Record, and index searches will
                      be Case sensitive.
                      if cleared, index tokens are all uppercase in
                      the Index Record, and index searches will ignore
                      case.
                      Defined With ;CASESENSE.

          MainIndexScreen - this is the number assigned to the conText
                      designated by the ;MAININDEX command in the help
                      source File.
                      if ;MAININDEX is not used, MainIndexScreen is set
                      to zero.

          MaxScreenSize - this is the number of Bytes in the longest Text
                      Record in the File (not including the header). This
                      field is not currently in use.

          Height, Width - This is the default size in rows and columns,
                      respectively, of the display area of a help Window.
                      Defined With ;HEIGHT and ;WIDTH.

          LeftMargin - Specifies the number of columns to leave blank on
                      the left edge of all rows of help Text displayed.
                      Defined With ;LEFTMARGIN.

     4.b ConText table -
      This is a table of Absolute File offsets that relates Help conTexts to their
      associated Text. The first Word of the Record gives the number of conTexts
      in the table.
      The remainder of the Record is a table of n ( n given by first Word) 3-Byte
      Integers (LSByte first). The table is indexed by conText number (0 to n-1).
      The 3-Byte Integer at a given index is an Absolute Byte that is offset in
      the Help File where the Text of the associated conText begins.
      The 3-Byte Integer is signed (2's complement).
      Two special values are defined -
            -1 use Index Screen Text (defined in File Header Record).
            -2 no help available For this conText.
      ConText table entry 0 is not used.

     4.c Text descriptions -
      The Text Record defines the compressed Text of conText.
      Text Records and keyWords appear in pairs, With one pair For each
      conText in the File. The Text Record always precedes its associated
      keyWord. Text Records are addressed through the File offset values
      found in the conText table described above.

      The RecLength field of the Text Record header defines the number
      of Bytes of compressed Text in the Record.
      The Compression Record defines how the Text is compressed.
      if the Text is nibble encoded, and the last nibble of the last Byte
      is not used, it is set to 0.
      Lines of Text comprising the the Text Record are stored as null
      terminated Strings.

     4.d the keyWord Record defines keyWords embedded in the preceeding Text
      Record, and identifies related Text Records.
      The Record begins With the following fixed fields:
        UpConText   : Word;
        DownConText : Word;
        KeyWordCnt  : Word;

      UpConText and DownConText give the conText numbers of the previous
      and next sections of Text in a sequence, either may be zero,
      indicating the end of the conText chain.

      KeyWordCnt gives the number of keyWords encoded in the associated
      Text Record.
      Immediately following this field is an Array of KeyWord Descriptor
      Records of the following form:
        Type
          TPKwDesc = Record;
            KwConText: Word;
          end;

      The keyWords in a Text Record are numbered from 1 to KeyWordCnt in the
      order they appear in the Text (reading left to right, top to bottom).

      KwConText is a conText number (index into the conText table) indicating
      which conText to switch to if this keyWord is selected by the user.

     4.e Index table -
      This is a list of index descriptors.
      An index is a token (normally a Word or name) that has been explicitly
      associated With a conText using the ;INDEX command in the source Text File.
      More than one index may be associated With a conText, but any given index
      can not be associated With more than one conText.
      The list of index descriptors in the Index Record allows the Text of an
      index token to be mapped into its associated conText number.

      The first Word of the Record gives the number of indexes defined in the
      Record.
      The remaining Bytes of the Record are grouped into index descriptors.
      The descriptors are listed in ascending order based on the Text of the index
      token (normal ascii collating sequence). if the OF_CaseSense flag is not set
      in the option field of the File header Record, all indexes are in uppercase
      only.

      Each index descriptor Uses the following format:
        LengthCode    : Byte;
        UniqueChars   : Array of Byte;
        ConTextNumber : Word;

      The bits of LengthCode are divided into two bit fields.
      Bits(7..5) specify the number of Characters to carry over from the start of
      the previous index token String.
      Bits(4..0) specify the number of unique Characters to add to the end of the
      inherited Characters.

      Field UniqueChars gives the number of unique Characters to add.
      e.g. if the previous index token is `addition', and the next index token is
      `advanced', we inherit two Characters from the previous token (ad), and add
      six Characters (vanced); thus LengthCode would be $46.

      ConTextNumber gives the number of the conText associated With the index.
      This number is an index into the conText table described above.

     4.f A compression Record defines how the contents of Text Records are
      encoded.
         Type
           TPCompress = Record
             CompType : Byte;
             CharTable: Array[0..13] of Byte;
           end;

      CompType - nibble encoding is the only compression method currently
                 in use.
                         Const CT_Nibble = 2;
      The Text is encoded as a stream of nibbles. The nibbles are stored
      sequentially; the low nibble preceeds the high nibble of a Byte.
      Nibble values ($0..$D) are direct indexes into the CharTable field of
      the compression Record. The indexed Record is the literal Character
      represented by the nibble. The Help Linker chooses the 14 (13?) most
      frequent Characters For inclusion in this table. One exception is that
      element 0 always maps to a Byte value of 0.

      The remaining two nibble values have special meanings:
              Const
                NC_RawChar = $F;
                NC_RepChar = $E;

      Nibble code NC_Char introduces two additional nibbles that define a
      literal Character; the least significant nibble first.

      Nibble code NC_RepChar defines a Repeated sequence of a single Character.
      The next nibble gives the Repeat count less two, (counts 2 to 17 are
      possible)
      The next nibble(s) define the Character to Repeat; it can be either a
      single nibble in the range ($0..$D) representing an index into
      CharTable, or it can be represented by a three nibble NC_RawChar
      sequence.

     4.g RT_IndexTags is in FormatVersion $34 only. This provides a means
      For including index sub headings in the help File.
      The Record header is followed by a list of Variable length tag Records
      Type
        IndRecType = Record;
          windexNumber: Word; {index into the RT_Index Record }
          StrLen: Byte;  {length of tag String(not including terminating 0)}
          szTag: Array[0..0] of Char; {disable range checking}{zero term tag
                                       String}
        end;
       The first structure in the Array is a special entry which has the
       windexnumber set to $FFFF, and contains the default ;DESCRIPTION
       in Case there are duplicate index entries and no tags were specified.
    *)

    Unit HelpGlobals;
    { This File contains only the structures which are found in the help Files }

    Interface

    Const
      Signature      = '$*$* &&&&*$';   {+ null terminator }
      NC_RawChar     = $F;
      NC_RepChar     = $E;

    Type
      FileStamp      = Array [0..32] Of Char; {+ null terminator + $1A }
      FileSignature  = Array [0..12] Of Char; {+ null terminator }

      TPVersion      = Record
        FormatVersion : Byte;
        TextVersion   : Byte;
      end;

      TPRecHdr       = Record
        RecType   : Byte; {TPRecType}
        RecLength : Word;
      end;

    Const   {RecType}
      RT_FileHeader  = Byte ($0);
      RT_ConText     = Byte ($1);
      RT_Text        = Byte ($2);
      RT_KeyWord     = Byte ($3);
      RT_Index       = Byte ($4);
      RT_Compression = Byte ($5);
      RT_IndexTags   = Byte ($6);

    Type
      TPIndRecType = Record
        windexNumber : Word;
        StrLen       : Byte;
        szTag        : Array [0..0] Of Char;
        { disable range checking}
      end;

      TPFileHdrRec = Record
        Options         : Word;
        MainIndexScreen : Word;
        Maxscreensize   : Word;
        Height          : Byte;
        Width           : Byte;
        LeftMargin      : Byte;
      end;

      TP4FileHdrRec = Record                  {derived from sample File}
        Options    : Word;
        Height     : Byte;
        Width      : Byte;
        LeftMargin : Byte;
      end;

      TPCompress = Record
        CompType  : Byte;
        CharTable : Array [0..13] Of Byte;
      end;

      TPIndexDescriptor = Record
        LengthCode    : Byte;
        UniqueChars   : Array [0..0] Of Byte;
        ConTextNumber : Word;
      end;

      TPKeyWord = Record
        UpConText   : Word;
        DownConText : Word;
        KeyWordCnt  : Word;
      end;

      TPKwDesc = Record
        KwConText : Word;
      end;

      TmyStream = Object(TBufStream) end;

      PListRecHdr = ^RListRecHdr;

      RListRecHdr = Record
        PNextHdr : PListRecHdr; {Pointer to next list element}
        RRecType : TPRecHdr;    {RecType, RecLength}
        PRecPtr  : Pointer;     {Pointer to copy of Record}
      end;

      ConTextRecHd = Record
        NoConTexts  : Word;
        PConTextRec : Pointer;
      end;

    Implementation
    end.

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