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using System;
using System.IO;
namespace Tango.AnimatedGif.Decoding
{
// label 0xF9
internal class GifGraphicControlExtension : GifExtension
{
internal const int ExtensionLabel = 0xF9;
public int BlockSize { get; private set; }
public int DisposalMethod { get; private set; }
public bool UserInput { get; private set; }
public bool HasTransparency { get; private set; }
public int Delay { get; private set; }
public int TransparencyIndex { get; private set; }
private GifGraphicControlExtension()
{
}
internal override GifBlockKind Kind
{
get { return GifBlockKind.Control; }
}
internal static GifGraphicControlExtension ReadGraphicsControl(Stream stream)
{
var ext = new GifGraphicControlExtension();
ext.Read(stream);
return ext;
}
private void Read(Stream stream)
{
// Note: at this point, the label (0xF9) has already been read
byte[] bytes = new byte[6];
stream.ReadAll(bytes, 0, bytes.Length);
BlockSize = bytes[0]; // should always be 4
if (BlockSize != 4)
throw GifHelpers.InvalidBlockSizeException("Graphic Control Extension", 4, BlockSize);
byte packedFields = bytes[1];
DisposalMethod = (packedFields & 0x1C) >> 2;
UserInput = (packedFields & 0x02) != 0;
HasTransparency = (packedFields & 0x01) != 0;
Delay = BitConverter.ToUInt16(bytes, 2) * 10; // milliseconds
TransparencyIndex = bytes[4];
}
}
}
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