/// <summary>
/// Constructor
/// </summary>
public Gif(ushort Width, ushort Height, ushort Repeat = 0)
{
CanvasWidth = Width;
CanvasHeight = Height;
Packed.Value = 0;
GlobalColorTable = new byte[0];
ApplicationExtension = new ExtensionNetscape(Repeat);
}
public static Type Extract(BinaryReader Reader, out Extension Extension)
{
Type type = (Type)Reader.ReadByte();
switch (type)
{
case Type.PlainText: Extension = new ExtensionGeneric(Reader); break; //todo
case Type.GraphicsControl: Extension = new ExtensionGraphicsControl(Reader); break;
case Type.Comment: Extension = new ExtensionGeneric(Reader); break; //todo
case Type.Application: Extension = ExtensionApplication.Extract(Reader); break;
default: Extension = new ExtensionGeneric(Reader); break;
}
return(type);
}
/// <summary>
/// Reads this Gif from a Stream
/// </summary>
/// <param name="Stream"></param>
public void Read(Stream Stream)
{
BinaryReader reader = new BinaryReader(
Stream, Encoding.ASCII, true);
//////////////////////////////////////////////
// HEADER
//////////////////////////////////////////////
byte[] buffer = new byte[3];
// signature
reader.Read(buffer, 0, 3);
if (!buffer.SequenceEqual(Constants.SIGNATURE))
{
throw new Exception("Not a GIF file");
}
// version
reader.Read(buffer, 0, 3);
// check version
if (!buffer.SequenceEqual(Constants.VERSION_89A) &&
!buffer.SequenceEqual(Constants.VERSION_87A))
{
throw new Exception("Unsupported Version");
}
//////////////////////////////////////////////
// LOGICAL SCREEN DESCRIPTOR DATA
//////////////////////////////////////////////
// width & height
CanvasWidth = reader.ReadUInt16();
CanvasHeight = reader.ReadUInt16();
// other data
Packed.Value = reader.ReadByte();
BackgroundColorIndex = reader.ReadByte();
PixelAspectRatio = reader.ReadByte();
//////////////////////////////////////////////
// GLOBAL COLOR TABLE (OPTIONAL)
//////////////////////////////////////////////
GlobalColorTable = (Packed.IsGlobalColorTable) ?
reader.ReadBytes((int)Packed.ByteSizeOfColorTable) :
new byte[0];
//////////////////////////////////////////////
// DYNAMIC CHUNKS (OPTIONAL, EXCEPT ONE FRAME)
//////////////////////////////////////////////
ExtensionGraphicsControl lastGraphicsControl = null;
while (true)
{
byte introducer = reader.ReadByte();
// EXTENSION
if (introducer == (byte)Introducer.Extension)
{
// try parse it
Extension extension;
Extension.Type type = Extension.Extract(reader, out extension);
// GraphicsControl
if (type == Extension.Type.GraphicsControl)
{
// save it for next frame
if (lastGraphicsControl == null)
{
lastGraphicsControl = (ExtensionGraphicsControl)extension;
}
// not good, we got another graphicscontrol extension
// without having read a frame since then...
else
{
// discard previous one, save this one
lastGraphicsControl = (ExtensionGraphicsControl)extension;
}
}
// Application
else if (type == Extension.Type.Application)
{
ApplicationExtension = (ExtensionApplication)extension;
}
// Generic
else
{
Extensions.Add(extension);
}
}
// IMAGEDESCRIPTOR
else if (introducer == (byte)Introducer.ImageDescriptor)
{
// parse frame data
Frame frame = new Frame(reader);
// attach the last GraphicsControl extension that was
// not used yet and last read before this frame
if (lastGraphicsControl != null)
{
frame.GraphicsControl = lastGraphicsControl;
lastGraphicsControl = null;
}
// store frame
Frames.Add(frame);
}
// TRAILER (PARSING SUCCESSFUL)
else if (introducer == (byte)Introducer.Trailer)
{
break;
}
// UNKNOWN
else
{
throw new Exception("Unknown Dynamic Chunk Introducer");
}
}
reader.Dispose();
}
