ScreenToGif/ImageUtil/Decoder/GifHelpers.cs

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using System;
using System.IO;
using System.Text;

namespace ScreenToGif.ImageUtil.Decoder
{
    public static class GifHelpers
    {
        public static string ReadString(Stream stream, int length)
        {
            byte[] bytes = new byte[length];
            stream.ReadAll(bytes, 0, length);
            return Encoding.ASCII.GetString(bytes);
        }

        public static byte[] ReadDataBlocks(Stream stream, bool discard)
        {
            MemoryStream ms = discard ? null : new MemoryStream();

            using (ms)
            {
                int len;

                while ((len = stream.ReadByte()) > 0)
                {
                    byte[] bytes = new byte[len];
                    stream.ReadAll(bytes, 0, len);

                    if (ms != null)
                        ms.Write(bytes, 0, len);
                }

                if (ms != null)
                    return ms.ToArray();

                return null;
            }
        }

        public static GifColor[] ReadColorTable(Stream stream, int size)
        {
            int length = 3 * size;
            byte[] bytes = new byte[length];
            stream.ReadAll(bytes, 0, length);
            GifColor[] colorTable = new GifColor[size];

            for (int i = 0; i < size; i++)
            {
                byte r = bytes[3 * i];
                byte g = bytes[3 * i + 1];
                byte b = bytes[3 * i + 2];
                colorTable[i] = new GifColor(r, g, b);
            }

            return colorTable;
        }

        public static bool IsNetscapeExtension(GifApplicationExtension ext)
        {
            return ext.ApplicationIdentifier == "NETSCAPE"