/// <summary>
        /// Reads all required tables from the font data.
        /// </summary>
        internal void Read()
        {
            // Determine font technology
            // ReSharper disable InconsistentNaming
            const uint OTTO = 0x4f54544f;  // Adobe OpenType CFF data, tag: 'OTTO'
            const uint TTCF = 0x74746366;  // TrueType Collection tag: 'ttcf'

            // ReSharper restore InconsistentNaming
            try
            {
#if DEBUG_
                if (Name == "Cambria")
                {
                    Debug - Break.Break();
                }
#endif

                // Check if data is a TrueType collection font.
                uint startTag = ReadULong();
                if (startTag == TTCF)
                {
                    _fontTechnology = FontTechnology.TrueTypeCollection;
                    throw new InvalidOperationException("TrueType collection fonts are not yet supported by PdfSharpCore.");
                }

                // Read offset table
                _offsetTable.Version       = startTag;
                _offsetTable.TableCount    = ReadUShort();
                _offsetTable.SearchRange   = ReadUShort();
                _offsetTable.EntrySelector = ReadUShort();
                _offsetTable.RangeShift    = ReadUShort();

                // Move to table dictionary at position 12
                Debug.Assert(_pos == 12);
                //tableDictionary = (offsetTable.TableCount);

                if (_offsetTable.Version == OTTO)
                {
                    _fontTechnology = FontTechnology.PostscriptOutlines;
                }
                else
                {
                    _fontTechnology = FontTechnology.TrueTypeOutlines;
                }

                for (int idx = 0; idx < _offsetTable.TableCount; idx++)
                {
                    TableDirectoryEntry entry = TableDirectoryEntry.ReadFrom(this);
                    TableDictionary.Add(entry.Tag, entry);
#if VERBOSE
                    Debug.WriteLine(String.Format("Font table: {0}", entry.Tag));
#endif
                }

                // PDFlib checks this, but it is not part of the OpenType spec anymore
                if (TableDictionary.ContainsKey("bhed"))
                {
                    throw new NotSupportedException("Bitmap fonts are not supported by PdfSharpCore.");
                }

                // Read required tables
                if (Seek(CMapTable.Tag) != -1)
                {
                    cmap = new CMapTable(this);
                }

                if (Seek(ControlValueTable.Tag) != -1)
                {
                    cvt = new ControlValueTable(this);
                }

                if (Seek(FontProgram.Tag) != -1)
                {
                    fpgm = new FontProgram(this);
                }

                if (Seek(MaximumProfileTable.Tag) != -1)
                {
                    maxp = new MaximumProfileTable(this);
                }

                if (Seek(NameTable.Tag) != -1)
                {
                    name = new NameTable(this);
                }

                if (Seek(FontHeaderTable.Tag) != -1)
                {
                    head = new FontHeaderTable(this);
                }

                if (Seek(HorizontalHeaderTable.Tag) != -1)
                {
                    hhea = new HorizontalHeaderTable(this);
                }

                if (Seek(HorizontalMetricsTable.Tag) != -1)
                {
                    hmtx = new HorizontalMetricsTable(this);
                }

                if (Seek(OS2Table.Tag) != -1)
                {
                    os2 = new OS2Table(this);
                }

                if (Seek(PostScriptTable.Tag) != -1)
                {
                    post = new PostScriptTable(this);
                }

                if (Seek(GlyphDataTable.Tag) != -1)
                {
                    glyf = new GlyphDataTable(this);
                }

                if (Seek(IndexToLocationTable.Tag) != -1)
                {
                    loca = new IndexToLocationTable(this);
                }

                if (Seek(GlyphSubstitutionTable.Tag) != -1)
                {
                    gsub = new GlyphSubstitutionTable(this);
                }

                if (Seek(ControlValueProgram.Tag) != -1)
                {
                    prep = new ControlValueProgram(this);
                }
            }
            catch (Exception)
            {
                GetType();
                throw;
            }
        }
        /// <summary>
        /// Adds the specified table to this font image.
        /// </summary>
        public void AddTable(OpenTypeFontTable fontTable)
        {
            if (!CanWrite)
            {
                throw new InvalidOperationException("Font image cannot be modified.");
            }

            if (fontTable == null)
            {
                throw new ArgumentNullException("fontTable");
            }

            if (fontTable._fontData == null)
            {
                fontTable._fontData = this;
            }
            else
            {
                Debug.Assert(fontTable._fontData.CanRead);
                // Create a reference to this font table
                fontTable = new IRefFontTable(this, fontTable);
            }

            //Debug.Assert(fontTable.FontData == null);
            //fontTable.fontData = this;

            TableDictionary[fontTable.DirectoryEntry.Tag] = fontTable.DirectoryEntry;
            switch (fontTable.DirectoryEntry.Tag)
            {
            case TableTagNames.CMap:
                cmap = fontTable as CMapTable;
                break;

            case TableTagNames.Cvt:
                cvt = fontTable as ControlValueTable;
                break;

            case TableTagNames.Fpgm:
                fpgm = fontTable as FontProgram;
                break;

            case TableTagNames.MaxP:
                maxp = fontTable as MaximumProfileTable;
                break;

            case TableTagNames.Name:
                name = fontTable as NameTable;
                break;

            case TableTagNames.Head:
                head = fontTable as FontHeaderTable;
                break;

            case TableTagNames.HHea:
                hhea = fontTable as HorizontalHeaderTable;
                break;

            case TableTagNames.HMtx:
                hmtx = fontTable as HorizontalMetricsTable;
                break;

            case TableTagNames.OS2:
                os2 = fontTable as OS2Table;
                break;

            case TableTagNames.Post:
                post = fontTable as PostScriptTable;
                break;

            case TableTagNames.Glyf:
                glyf = fontTable as GlyphDataTable;
                break;

            case TableTagNames.Loca:
                loca = fontTable as IndexToLocationTable;
                break;

            case TableTagNames.GSUB:
                gsub = fontTable as GlyphSubstitutionTable;
                break;

            case TableTagNames.Prep:
                prep = fontTable as ControlValueProgram;
                break;
            }
        }