/// <summary>
/// Writes GIF metadata into extension blocks.
/// </summary>
protected void WriteMetadata()
{
Blocks.RemoveAll(b => b as GIFCommentExtension != null);
foreach (var prop in Properties)
{
if (prop.Tag == ExifTag.GIFComment)
{
var gifComment = prop as GIFComment;
if (gifComment != null)
{
var block = new GIFCommentExtension();
var interop = gifComment.Interoperability;
if (interop.Count == 0)
{
continue;
}
var subBlockCount = (interop.Count - 1) / 255 + 1;
block.Data = new byte[subBlockCount][];
int offset = 0;
for (int i = 0; i < subBlockCount; i++)
{
int count = Math.Min(255, interop.Data.Length - offset);
block.Data[i] = new byte[count];
Array.Copy(interop.Data, offset, block.Data[i], 0, count);
offset += count;
}
var insertBefore = gifComment.InsertBefore;
int index = insertBefore == null ? -1 : Blocks.IndexOf(insertBefore);
if (index == -1)
{
index = Blocks[Blocks.Count - 1].Separator == GIFSeparator.Terminator ? Blocks.Count - 1 : Blocks.Count;
}
Blocks.Insert(index, block);
index++;
}
}
}
}
/// <summary>
/// Initializes a new instance of the <see cref="GIFFile"/> class from the
/// specified data stream.
/// </summary>
/// <param name="stream">A stream that contains image data.</param>
/// <param name="encoding">The encoding to be used for text metadata when the source encoding is unknown.</param>
protected internal GIFFile(MemoryStream stream, System.Text.Encoding encoding)
{
Format = ImageFileFormat.GIF;
Blocks = new List <GIFBlock>();
var conv = BitConverterEx.LittleEndian;
stream.Seek(0, SeekOrigin.Begin);
// version
var versionBytes = Utility.GetStreamBytes(stream, 6);
Version = Encoding.ASCII.GetString(versionBytes, 3, 3);
// screen descriptor
ScreenWidth = conv.ToUInt16(Utility.GetStreamBytes(stream, 2), 0);
ScreenHeight = conv.ToUInt16(Utility.GetStreamBytes(stream, 2), 0);
var sdByte = (byte)stream.ReadByte();
// global color table flag in bit 7
HasGCT = (sdByte & (1 << 7)) != 0;
// color resolution in bits 6, 5, 4
int b6 = (sdByte & (1 << 6));
int b5 = (sdByte & (1 << 5));
int b4 = (sdByte & (1 << 4));
ColorResolution = (byte)(((b6 | b5 | b4) >> 4) + 1);
// global color table sorted flag in bit 3
IsGCTSorted = (sdByte & (1 << 3)) != 0;
// global color table size bits 2, 1, 0
int b2 = (sdByte & (1 << 2));
int b1 = (sdByte & (1 << 1));
int b0 = (sdByte & (1 << 0));
SizeOfGCT = (byte)((b2 | b1 | b0) + 1);
BackcolorIndex = (byte)stream.ReadByte();
PixelAspectRatio = (byte)stream.ReadByte();
// global color table
GCT = ReadColorTable(stream, HasGCT ? MathEx.Power2(SizeOfGCT) : 0);
// Search and read blocks until we reach the end of file.
while (stream.Position != stream.Length)
{
int val = stream.ReadByte();
if (val == -1)
{
break;
}
byte separator = (byte)val;
if (separator == 0x3B)
{
// end of image
Blocks.Add(new GIFTerminator());
break;
}
else if (separator == 0x2C)
{
// image descriptor block
var block = new GIFImageDescriptor();
block.Left = conv.ToUInt16(Utility.GetStreamBytes(stream, 2), 0);
block.Top = conv.ToUInt16(Utility.GetStreamBytes(stream, 2), 0);
block.Width = conv.ToUInt16(Utility.GetStreamBytes(stream, 2), 0);
block.Height = conv.ToUInt16(Utility.GetStreamBytes(stream, 2), 0);
var idByte = (byte)stream.ReadByte();
// local color table flag in bit 7
block.HasLCT = (idByte & (1 << 7)) != 0;
// interlaced flag in bit 6
block.IsInterlaced = (idByte & (1 << 6)) != 0;
// local color table sorted flag in bit 5
block.IsLCTSorted = (idByte & (1 << 5)) != 0;
// reserved value in bits 4, 3
int id4 = (idByte & (1 << 4));
int id3 = (idByte & (1 << 3));
block.Reserved = (byte)((id4 | id3) >> 3);
// local color table size bits 2, 1, 0
int id2 = (idByte & (1 << 2));
int id1 = (idByte & (1 << 1));
int id0 = (idByte & (1 << 0));
block.SizeOfLCT = (byte)((id2 | id1 | id0) + 1);
// local color table
block.LCT = ReadColorTable(stream, block.HasLCT ? MathEx.Power2(block.SizeOfLCT) : 0);
// raster data
block.LZWMinimumCodeSize = (byte)stream.ReadByte();
block.ImageData = ReadDataBlock(stream);
Blocks.Add(block);
}
else if (separator == 0x21)
{
// extension block
val = stream.ReadByte();
if (val == -1)
{
break;
}
var label = (byte)val;
if (label == 0xF9)
{
// graphic control extension
var size = stream.ReadByte();
var block = new GIFGraphicControlExtension();
var geByte = (byte)stream.ReadByte();
// reserved value in bits 7, 6, 5
int ge7 = (geByte & (1 << 7));
int ge6 = (geByte & (1 << 6));
int ge5 = (geByte & (1 << 5));
block.Reserved = (byte)((ge7 | ge6 | ge5) >> 5);
// disposal method in bits 4, 3, 2
int ge4 = (geByte & (1 << 4));
int ge3 = (geByte & (1 << 3));
int ge2 = (geByte & (1 << 2));
block.DisposalMethod = (byte)((ge4 | ge3 | ge2) >> 2);
// user input flag in bit 1
block.UserInputFlag = (geByte & (1 << 1)) != 0;
// transparent color flag in bit 0
block.TransparentColorFlag = (geByte & (1 << 0)) != 0;
block.DelayTime = conv.ToUInt16(Utility.GetStreamBytes(stream, 2), 0);
block.TransparentColorIndex = (byte)stream.ReadByte();
var term = stream.ReadByte();
Blocks.Add(block);
}
else if (label == 0xFE)
{
// comment extension
var block = new GIFCommentExtension();
// comment data
block.Data = ReadDataBlock(stream);
Blocks.Add(block);
}
else if (label == 0x01)
{
// plain text extension
var block = new GIFPlainTextExtension();
var size = stream.ReadByte();
block.Left = conv.ToUInt16(Utility.GetStreamBytes(stream, 2), 0);
block.Top = conv.ToUInt16(Utility.GetStreamBytes(stream, 2), 0);
block.Width = conv.ToUInt16(Utility.GetStreamBytes(stream, 2), 0);
block.Height = conv.ToUInt16(Utility.GetStreamBytes(stream, 2), 0);
block.CellWidth = (byte)stream.ReadByte();
block.CellHeight = (byte)stream.ReadByte();
block.ForegroundColorIndex = (byte)stream.ReadByte();
block.BackgroundColorIndex = (byte)stream.ReadByte();
// plain text data
block.Data = ReadDataBlock(stream);
Blocks.Add(block);
}
else if (label == 0xFF)
{
// application extension
var block = new GIFApplicationExtension();
var size = stream.ReadByte();
block.ApplicationIdentifier = Utility.GetStreamBytes(stream, 8);
block.AuthenticationCode = Utility.GetStreamBytes(stream, 3);
// application data
block.Data = ReadDataBlock(stream);
Blocks.Add(block);
}
else
{
// unkown extension block
var block = new GIFExtensionBlock(label);
block.Data = ReadDataBlock(stream);
Blocks.Add(block);
}
}
else
{
// unknown block
throw new NotValidGIFFileException(string.Format("Unkown GIF block separator: 0x{0:X}", separator));
}
}
// insert a terminator if it doesn't exist
if (Blocks[Blocks.Count - 1].Separator != GIFSeparator.Terminator)
{
Blocks.Add(new GIFTerminator());
}
// process metadata
ReadMetadata();
}
