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using System;
using System.IO;
namespace Tango.AnimatedGif.Decoding
{
internal class GifLogicalScreenDescriptor
{
public int Width { get; private set; }
public int Height { get; private set; }
public bool HasGlobalColorTable { get; private set; }
public int ColorResolution { get; private set; }
public bool IsGlobalColorTableSorted { get; private set; }
public int GlobalColorTableSize { get; private set; }
public int BackgroundColorIndex { get; private set; }
public double PixelAspectRatio { get; private set; }
internal static GifLogicalScreenDescriptor ReadLogicalScreenDescriptor(Stream stream)
{
var descriptor = new GifLogicalScreenDescriptor();
descriptor.Read(stream);
return descriptor;
}
private void Read(Stream stream)
{
byte[] bytes = new byte[7];
stream.ReadAll(bytes, 0, bytes.Length);
Width = BitConverter.ToUInt16(bytes, 0);
Height = BitConverter.ToUInt16(bytes, 2);
byte packedFields = bytes[4];
HasGlobalColorTable = (packedFields & 0x80) != 0;
ColorResolution = ((packedFields & 0x70) >> 4) + 1;
IsGlobalColorTableSorted = (packedFields & 0x08) != 0;
GlobalColorTableSize = 1 << ((packedFields & 0x07) + 1);
BackgroundColorIndex = bytes[5];
PixelAspectRatio =
bytes[5] == 0
? 0.0
: (15 + bytes[5]) / 64.0;
}
}
}
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