DRS files

DRS format

drs files are archives containing other files, like a tar archive, but much simpler. Helpfully, the format is sequential in nature, which helps speed up decoding time.

DRS Header

A DRS file starts with its main header:

Length Type Description Example
40 bytes string Copyright info Copyright (c) 1997 Ensemble Studios\032.
4 bytes string File version 1.00
12 bytes string File type tribe
4 bytes int32 Number of tables 4, 0x00000004
4 bytes int32 Offset of 1st file 2188, 0x0000088C 
struct drs_header {
	char copyright[40];
	char version[4];
	char ftype[12];
	int32 table_count;
	int32 file_offset;
};

Python format: Struct("< 40s 4s 12s i i")

  • It is important to note that in later versions of the DRS format (used for SW:GB), it appears that copyright has a length of 60 instead of the usual 40.

  • copyright, version & ftype seem to always have the same value.

  • table_count stores how many drs_table_info structs will follow the main header.

  • file_offset is the offset of the first actual file in the DRS.

DRS Table info

One drs_table_info struct is stored for each file type (Possible file extensions are bina, slp , wav ).

Length Type Description Example
4 bytes string File extension 'anib', ' pls'
4 bytes int32 Table offset 112, 0x00000070
4 bytes int32 Number of files 71, 0x00000047 
struct drs_table_info {
	char file_extension[4];
	int32 file_info_offset;
	int32 num_files;
};

Python format: Struct("< 4s i i")

  • file_extension is reversed and padded by spaces (0x20) to reach 4 bytes. Internally, Age of Empires does something like this when reading files from a DRS archive:

    read_drs_file('bina', 50500);

    Note how it uses a C char with multiple bytes. This is stored on disk as a little-endian integer, so the ‘a’ byte ends up at the lowest address, and the ‘b’ byte ends up at the highest address.

  • file_info_offset holds the offset where the actual table resides.

  • num_files contains the amount of files in the table.

The drs_table_info tells us, how many files are stored for the file_type.

DRS File info

Each table contains entries for the files in it. The table entry consists of: the unique integer identifier of the embedded file, the offset of the embedded file and the size of the embedded file.

drs_file_info tables start at position drs_table_info->file_info_offset for the corresponding table:

Length Type Description Example
4 bytes int32 File id 50001, 0x0000C351
4 bytes int32 File offset 2188, 0x0000088C
4 bytes int32 File size 625, 0x00000271 
struct drs_file_info {
	int32 file_id;
	int32 file_data_offset;
	int32 file_size;
};

Python format: Struct("< i i i")

For every file, the offset in the .drs is stored, and also its size. The file’s ID can be assumed to be its name.

Files

DRS files that come with the base AoK game.

gamedata.drs

Contains random map scripts (RMS), as well as AI scripts and some graphic files. Random Map scripts describe how the builtin maps should be generated. AI scripts tell the computer what to do, such as build units, gather resources, and generally make it “smart”. These are all bina files. The graphic files (slp) are described below.

graphics.drs

Contains almost every graphic you see in the game. This includes units, buildings, resources, animals, cliffs and shadows. These are all slp graphic (animation) files.

interfac.drs

Contains the main interface graphics of the game. All of the the borders, buttons, logos, main game screen, etc you see when entering the game to starting one can be found within this file as slp graphics. The drawing color palettes are also stored in this file as bina. Finally there’s a bunch of wav sounds, too.

sounds.drs

Contains every sound in Age of Kings. These are all wav files.

terrain.drs

Contains all the terrain, in diamond shaped pieces. For each terrain, there are 100 pieces. These are all slp files.