/// <summary>
/// Writes the graphics control extension to the stream.
/// </summary>
/// <param name="metaData">The metadata of the image or frame.</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(ImageFrameMetaData metaData, EndianBinaryWriter writer, int transparencyIndex)
{
var extension = new GifGraphicsControlExtension
{
DisposalMethod = metaData.DisposalMethod,
TransparencyFlag = transparencyIndex > -1,
TransparencyIndex = unchecked ((byte)transparencyIndex),
DelayTime = metaData.FrameDelay
};
// Write the intro.
this.buffer[0] = GifConstants.ExtensionIntroducer;
this.buffer[1] = GifConstants.GraphicControlLabel;
this.buffer[2] = 4;
writer.Write(this.buffer, 0, 3);
var field = default(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(extension.TransparencyIndex);
writer.Write(GifConstants.Terminator);
}
/// <summary>
/// Reads the graphic control extension.
/// </summary>
private void ReadGraphicalControlExtension()
{
this.currentStream.Read(this.buffer, 0, 6);
byte packed = this.buffer[1];
this.graphicsControlExtension = new GifGraphicsControlExtension
{
DelayTime = BitConverter.ToInt16(this.buffer, 2),
TransparencyIndex = this.buffer[4],
TransparencyFlag = (packed & 0x01) == 1,
DisposalMethod = (DisposalMethod)((packed & 0x1C) >> 2)
};
}
/// <summary>
/// Reads the graphic control extension.
/// </summary>
private void ReadGraphicalControlExtension()
{
this.currentStream.Read(this.buffer, 0, 6);
this.graphicsControlExtension = GifGraphicsControlExtension.Parse(this.buffer);
}
