/// <summary>
/// Reads the graphic control extension.
/// </summary>
private void ReadGraphicalControlExtension()
{
byte[] buffer = new byte[6];
this.currentStream.Read(buffer, 0, buffer.Length);
byte packed = buffer[1];
this.graphicsControlExtension = new GifGraphicsControlExtension
{
DelayTime = BitConverter.ToInt16(buffer, 2),
TransparencyIndex = buffer[4],
TransparencyFlag = (packed & 0x01) == 1,
DisposalMethod = (DisposalMethod)((packed & 0x1C) >> 2)
};
}
/// <summary>
/// Writes the graphics control extension to the stream.
/// </summary>
/// <typeparam name="T">The pixel format.</typeparam>
/// <typeparam name="TP">The packed format. <example>long, float.</example></typeparam>
/// <param name="image">The <see cref="ImageBase{T,TP}"/> to encode.</param>
/// <param name="writer">The stream to write to.</param>
/// <param name="transparencyIndex">The index of the color in the color palette to make transparent.</param>
private void WriteGraphicalControlExtension <T, TP>(ImageBase <T, TP> image, EndianBinaryWriter writer, int transparencyIndex)
where T : IPackedVector <TP>
where TP : struct
{
// TODO: Check transparency logic.
bool hasTransparent = transparencyIndex > -1;
DisposalMethod disposalMethod = hasTransparent
? DisposalMethod.RestoreToBackground
: DisposalMethod.Unspecified;
GifGraphicsControlExtension extension = new GifGraphicsControlExtension()
{
DisposalMethod = disposalMethod,
TransparencyFlag = hasTransparent,
TransparencyIndex = transparencyIndex,
DelayTime = image.FrameDelay
};
// Reduce the number of writes.
byte[] intro =
{
GifConstants.ExtensionIntroducer,
GifConstants.GraphicControlLabel,
4 // Size
};
writer.Write(intro);
PackedField field = new PackedField();
field.SetBits(3, 3, (int)extension.DisposalMethod); // 1-3 : Reserved, 4-6 : Disposal
// TODO: Allow this as an option.
field.SetBit(6, false); // 7 : User input - 0 = none
field.SetBit(7, extension.TransparencyFlag); // 8: Has transparent.
writer.Write(field.Byte);
writer.Write((ushort)extension.DelayTime);
writer.Write((byte)(extension.TransparencyIndex == -1 ? 255 : extension.TransparencyIndex));
writer.Write(GifConstants.Terminator);
}
/// <summary>
/// Writes the graphics control extension to the stream.
/// </summary>
/// <param name="image">The <see cref="ImageBase"/> to encode.</param>
/// <param name="stream">The stream to write to.</param>
private void WriteGraphicalControlExtension(ImageBase image, Stream stream)
{
// Calculate the quality.
int quality = this.Quality > 0 ? this.Quality : image.Quality;
quality = quality > 0 ? quality.Clamp(1, 256) : 256;
// TODO: Check transparency logic.
bool hasTransparent = quality > 1;
DisposalMethod disposalMethod = hasTransparent
? DisposalMethod.RestoreToBackground
: DisposalMethod.Unspecified;
GifGraphicsControlExtension extension = new GifGraphicsControlExtension()
{
DisposalMethod = disposalMethod,
TransparencyFlag = hasTransparent,
TransparencyIndex = quality - 1, // Quantizer sets last index as transparent.
DelayTime = image.FrameDelay
};
this.WriteByte(stream, GifConstants.ExtensionIntroducer);
this.WriteByte(stream, GifConstants.GraphicControlLabel);
this.WriteByte(stream, 4); // Size
int packed = 0 | // 1-3 : Reserved
(int)extension.DisposalMethod << 2 | // 4-6 : Disposal
0 | // 7 : User input - 0 = none
(extension.TransparencyFlag ? 1 : 0); // 8: Has transparent.
this.WriteByte(stream, packed);
this.WriteShort(stream, extension.DelayTime);
this.WriteByte(stream, extension.TransparencyIndex);
this.WriteByte(stream, GifConstants.Terminator);
}
