private const int MaxSectionSizeBuffer = 10; // the maximum size of 2 MC values
public void Write(BitWriter writer)
{
void WriteSection(byte[] data)
{
writer.StartCrcCalculation(initialValue: DwgHeaderVariables.InitialCrcValue);
writer.WriteShortBigEndian((short)(data.Length + 2)); // account for crc
writer.WriteBytes(data);
writer.WriteCrc(writeCrcAsMsb: true);
}
// write in sections, each section is at most 2032 bytes, stop writing if remaining space is less than 10
var sectionStart = writer.Position;
var lastHandle = 0;
var lastLocation = 0;
var ms = new MemoryStream();
var sectionWriter = new BitWriter(ms);
foreach (var kvp in _handleOffsets.OrderBy(k => k.Key))
{
var sectionSize = writer.Position - sectionStart;
if (sectionSize >= MaxSectionSize - MaxSectionSizeBuffer)
{
// flush section
var sectionBytes = sectionWriter.AsBytes();
WriteSection(sectionBytes);
ms.Dispose();
ms = new MemoryStream();
sectionWriter = new BitWriter(ms);
sectionStart = writer.Position;
}
// now write the values
var handleDiff = kvp.Key - lastHandle;
var locationDiff = kvp.Value - lastLocation;
sectionWriter.Write_MC(handleDiff);
sectionWriter.Write_MC(locationDiff);
lastHandle = kvp.Key;
lastLocation = kvp.Value;
}
// flush the final section
var finalBytes = sectionWriter.AsBytes();
if (finalBytes.Length > 0)
{
WriteSection(finalBytes);
}
ms.Dispose();
// always finish with an empty section
WriteSection(new byte[0]);
}
internal void Write(BitWriter writer, DwgVersionId version)
{
writer.AlignByte();
using (var ms = new MemoryStream())
{
// write the variables to memory
var variableWriter = new BitWriter(ms);
WriteVariables(variableWriter, version);
var variableBytes = variableWriter.AsBytes();
// now write it all out
writer.WriteBytes(StartSentinel);
writer.StartCrcCalculation(initialValue: InitialCrcValue);
writer.Write_RL(variableBytes.Length);
writer.WriteBytes(variableBytes);
writer.WriteCrc();
writer.WriteBytes(EndSentinel);
}
}
internal static void Write(IList <DwgClassDefinition> classes, BitWriter writer)
{
writer.AlignByte();
using (var ms = new MemoryStream())
{
// write the classes to memory
var classWriter = new BitWriter(ms);
foreach (var c in classes)
{
c.Write(classWriter);
}
var classBytes = classWriter.AsBytes();
// now write it all out
writer.WriteBytes(StartSentinel);
writer.StartCrcCalculation(initialValue: DwgHeaderVariables.InitialCrcValue);
writer.Write_RL(classBytes.Length);
writer.WriteBytes(classBytes);
writer.WriteCrc();
writer.WriteBytes(EndSentinel);
}
}
internal void WriteSecondHeader(BitWriter writer, DwgHeaderVariables headerVariables, int pointer)
{
// write to memory the backtrack to fill in size and crc
using (var ms = new MemoryStream())
{
var tempWriter = new BitWriter(ms);
tempWriter.WriteBytes(SecondHeaderStartSentinel);
var sizeOffset = tempWriter.Position;
tempWriter.Write_RL(0); // size, filled in later
tempWriter.Write_BL(pointer);
tempWriter.WriteStringAscii(Version.VersionString(), nullTerminated: false);
tempWriter.WriteBytes(new byte[] { 0, 0, 0, 0, 0, 0 }); // 6 zero bytes
tempWriter.WriteBits(0x00000000, 4); // 4 zero bits
tempWriter.WriteBytes(new byte[] { 0, 0 }); // 2 unknown bytes
tempWriter.WriteBytes(SecondHeaderMidSentinel);
tempWriter.WriteByte(5); // record locator count
HeaderVariablesLocator.Write(tempWriter, writingSecondHeader: true);
ClassSectionLocator.Write(tempWriter, writingSecondHeader: true);
ObjectMapLocator.Write(tempWriter, writingSecondHeader: true);
UnknownSection_R13C3AndLaterLocator.Write(tempWriter, writingSecondHeader: true);
UnknownSection_PaddingLocator.Write(tempWriter, writingSecondHeader: true);
tempWriter.Write_BS(14);
headerVariables.NextAvailableHandle.WriteSecondHeader(tempWriter, 0);
headerVariables.BlockControlObjectHandle.WriteSecondHeader(tempWriter, 1);
headerVariables.LayerControlObjectHandle.WriteSecondHeader(tempWriter, 2);
headerVariables.StyleObjectControlHandle.WriteSecondHeader(tempWriter, 3);
headerVariables.LineTypeObjectControlHandle.WriteSecondHeader(tempWriter, 4);
headerVariables.ViewControlObjectHandle.WriteSecondHeader(tempWriter, 5);
headerVariables.UcsControlObjectHandle.WriteSecondHeader(tempWriter, 6);
headerVariables.ViewPortControlObjectHandle.WriteSecondHeader(tempWriter, 7);
headerVariables.AppIdControlObjectHandle.WriteSecondHeader(tempWriter, 8);
headerVariables.DimStyleControlObjectHandle.WriteSecondHeader(tempWriter, 9);
headerVariables.ViewPortEntityHeaderControlObjectHandle.WriteSecondHeader(tempWriter, 10);
headerVariables.NamedObjectsDictionaryHandle.WriteSecondHeader(tempWriter, 11);
headerVariables.MLineStyleDictionaryHandle.WriteSecondHeader(tempWriter, 12);
headerVariables.GroupDictionaryHandle.WriteSecondHeader(tempWriter, 13);
tempWriter.WriteByte(0); // unknown
tempWriter.AlignByte();
var crcOffset = tempWriter.Position;
tempWriter.WriteShort(0); // CRC, filled in later
if (Version == DwgVersionId.R14)
{
// unknown garbage bytes
tempWriter.WriteBytes(new byte[] { 0, 0, 0, 0, 0, 0, 0, 0 });
}
tempWriter.WriteBytes(SecondHeaderEndSentinel);
// get bytes of header
var secondHeaderBytes = tempWriter.AsBytes();
// fill in size
var sizeBytes = BitConverter.GetBytes(secondHeaderBytes.Length - SecondHeaderStartSentinel.Length - SecondHeaderEndSentinel.Length);
if (!BitConverter.IsLittleEndian)
{
Array.Reverse(sizeBytes);
}
Array.Copy(sizeBytes, 0, secondHeaderBytes, sizeOffset, sizeBytes.Length);
// fill in crc
var crc = BitReaderExtensions.ComputeCRC(secondHeaderBytes, sizeOffset, crcOffset - sizeOffset, DwgHeaderVariables.InitialCrcValue);
var crcBytes = BitConverter.GetBytes(crc);
if (!BitConverter.IsLittleEndian)
{
Array.Reverse(crcBytes);
}
Array.Copy(crcBytes, 0, secondHeaderBytes, crcOffset, crcBytes.Length);
// write to the real writer
writer.WriteBytes(secondHeaderBytes);
}
}