private void ReadVisData( InternalBspLump lump, BinaryReader reader )
{
reader.BaseStream.Seek( lump.offset, SeekOrigin.Begin );
visData = new InternalBspVis();
visData.clusterCount = reader.ReadInt32();
visData.rowSize = reader.ReadInt32();
visData.data = reader.ReadBytes( lump.offset - ( Marshal.SizeOf( typeof( int ) ) * 2 ) );
}