/// <summary>
/// Reads the Offset and Directory tables. If the FontFileStream represents
/// a TrueType collection, this method will look for the aforementioned
/// tables belonging to <i>fontName</i>.
/// </summary>
/// <remarks>
/// This method can handle a TrueType collection.
/// </remarks>
protected void ReadTableHeaders()
{
// Check for possible TrueType collection
string tag = Encoding.ASCII.GetString(stream.ReadTag());
if (tag == TableNames.Ttcf)
{
// Skip Version field - will be either 1.0 or 2.0
stream.Skip(PrimitiveSizes.ULong);
// Number of fonts in TrueType collection
int numFonts = (int)stream.ReadULong();
bool foundFont = false;
for (int i = 0; i < numFonts && !foundFont; i++)
{
// Offset from beginning of file to a font's subtable
uint directoryOffset = stream.ReadULong();
// Set a restore point since the code below will alter the stream position
stream.SetRestorePoint();
stream.Position = directoryOffset;
header = new TrueTypeHeader();
header.Read(stream);
// To ascertain whether this font is the one we're looking for,
// we must read the 'name' table.
if (!header.Contains(TableNames.Name))
{
throw new Exception("Unable to parse TrueType collection - missing 'head' table.");
}
// If font name is not supplied, select the first font in the colleciton;
// otherwise must have an exact match
NameTable nameTable = (NameTable)GetTable(TableNames.Name);
if (fontName == String.Empty || nameTable.FullName == fontName)
{
foundFont = true;
}
// Stream will now point to the next directory offset
stream.Restore();
}
// We were unable to locate font in collection
if (!foundFont)
{
throw new Exception("Unable to locate font '" + fontName + "' in TrueType collection");
}
}
else
{
stream.Position = 0;
// Read Offset and Directory tables
header = new TrueTypeHeader();
header.Read(stream);
}
}
private void WriteFontTable(FontTable table)
{
// Start position required to generate checksum and length
long startPosition = stream.SetRestorePoint();
// FontTable subclass is responsible for writing itself
table.Write(this);
// Align table on 4-byte boundary
int padding = stream.Pad();
// Restore will reset stream position back to startPosition
long endPosition = stream.Restore();
// The table length not including the padding
table.Entry.Length = (uint)(endPosition - startPosition - padding);
table.Entry.Offset = (uint)startPosition;
table.Entry.CheckSum = CalculateCheckSum(table.Entry.Length);
}
/// <summary>
/// Reads a string from the storage area beginning at <i>offset</i>
/// consisting of <i>length</i> bytes. The returned string will be
/// converted using the Unicode encoding.
/// </summary>
/// <param name="stream">Big-endian font stream.</param>
/// <param name="stringOffset">
/// The offset in bytes from the beginning of the string storage area.
/// </param>
/// <param name="length">The length of the string in bytes.</param>
/// <returns></returns>
private string ReadString(FontFileStream stream, int stringOffset, int length)
{
// Set a restore point
stream.SetRestorePoint();
// Navigate to beginning of string
stream.Position = Entry.Offset + storageOffset + stringOffset;
// Read string data
byte[] buffer = new byte[length];
stream.Read(buffer, 0, length);
stream.Restore();
// Convert to a little-endian Unicode string
return(Encoding.BigEndianUnicode.GetString(buffer));
}
/// <summary>
/// Reads a string from the storage area beginning at <i>offset</i>
/// consisting of <i>length</i> bytes. The returned string will be
/// converted using the Unicode encoding.
/// </summary>
/// <param name="stream">Big-endian font stream.</param>
/// <param name="stringOffset">
/// The offset in bytes from the beginning of the string storage area.
/// </param>
/// <param name="length">The length of the string in bytes.</param>
/// <returns></returns>
private string ReadString(FontFileStream stream, int stringOffset, int length) {
// Set a restore point
stream.SetRestorePoint();
// Navigate to beginning of string
stream.Position = Entry.Offset + storageOffset + stringOffset;
// Read string data
byte[] buffer = new byte[length];
stream.Read(buffer, 0, length);
stream.Restore();
// Convert to a little-endian Unicode string
return Encoding.BigEndianUnicode.GetString(buffer);
}
