Yunan.WPF.ImageAnim.GifAnimation.ParseBlock C# (CSharp) Method

        private int ParseBlock(byte[] gifData, int offset)
        {
            switch (gifData[offset])
            {
                case 0x21:
                    if (gifData[offset + 1] == 0xF9)
                    {
                        return ParseGraphicControlExtension(gifData, offset);
                    }
                    else
                    {
                        return ParseExtensionBlock(gifData, offset);
                    }
                case 0x2C:
                    offset = ParseGraphicBlock(gifData, offset);
                    _frameList.Add(_currentParseGifFrame);
                    _currentParseGifFrame = new GifFrame();
                    return offset;
                case 0x3B:
                    return -1;
                default:
                    throw new Exception("GIF format incorrect: missing graphic block or special-purpose block. ");
            }
        }