public GifImageDescriptor ReadImageDescriptor()
{
AssertToken(Token.ImageDescriptor);
imageDescriptor.left = currentStream.ReadInt16LittleEndian();
imageDescriptor.top = currentStream.ReadInt16LittleEndian();
imageDescriptor.width = currentStream.ReadInt16LittleEndian();
imageDescriptor.height = currentStream.ReadInt16LittleEndian();
var flags = currentStream.ReadByte8();
imageDescriptor.localColorTableSize = BitUtils.GetColorTableSize(flags.GetBitsFromByte(0, 3));
imageDescriptor.isInterlaced = flags.GetBitFromByte(6);
imageDescriptor.hasLocalColorTable = flags.GetBitFromByte(7);
if (imageDescriptor.hasLocalColorTable)
{
nextPaletteIsGlobal = false;
SetCurrentToken(Token.Palette);
}
else
{
SetCurrentToken(Token.Image);
}
return(imageDescriptor);
}
/// <summary>
/// Read gif header
/// </summary>
/// <returns>Data of gif header</returns>
/// <exception cref="ArgumentException">If file is not gif file</exception>
public GifHeader ReadHeader()
{
AssertToken(Token.Header);
// Header
headerStartPosition = currentStream.Position;
firstFrameStartPosition = -1;
currentStream.Read(headerBuffer, 0, headerBuffer.Length);
if (BitUtils.CheckString(headerBuffer, "GIF87a"))
{
header.version = GifVersion.Gif87a;
}
else if (BitUtils.CheckString(headerBuffer, "GIF89a"))
{
header.version = GifVersion.Gif89a;
}
else
{
throw new ArgumentException("Invalid or corrupted Gif file");
}
// Screen descriptor
header.width = currentStream.ReadInt16LittleEndian();
header.height = currentStream.ReadInt16LittleEndian();
var flags = currentStream.ReadByte8();
header.globalColorTableSize = BitUtils.GetColorTableSize(flags.GetBitsFromByte(0, 3));
header.sortColors = flags.GetBitFromByte(3);
header.colorResolution = flags.GetBitsFromByte(4, 3);
header.hasGlobalColorTable = flags.GetBitFromByte(7);
header.transparentColorIndex = currentStream.ReadByte8();
header.pixelAspectRatio = currentStream.ReadByte8();
canvas.SetSize(header.width, header.height);
if (header.hasGlobalColorTable)
{
SetCurrentToken(Token.Palette);
nextPaletteIsGlobal = true;
}
else
{
DetermineNextToken();
}
return(header);
}
