OBD:Instance file format

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The Raw and separate file formats page should be read after this one.

Files in GameDataFolder/ named "level[0-19]_Final.dat", together with ".raw" and sometimes ".sep" counterparts, contain the game data for Oni.

The same format was used for the tool files, named level0_Tools.dat/.raw/.sep, however the retail Oni game application does not load tool files; for the story behind the tool files, see HERE.

The level 0 files do not actually contain a level, but instances (resources) shared across all levels. Level 0 is loaded when the game starts, and never unloaded. All other level files, 1-19, are only loaded when their corresponding level starts, and unloaded when it ends. Since Oni can only hold these two levels in memory concurrently, resources have to be duplicated on disk whenever a character class, sound effect, etc. occurs in more than one level. For instance, although there are only 2,380 unique sounds in the game, there are 7,386 sounds stored across all level data files.

Backwards and garbage data

During development, Oni had an in-game editor which presented a GUI for manipulating AIs, particles, etc. in a level. When a developer saved his work, the contents of the level, stored in RAM, were written directly to disk. Thus, the structure of the .dat/.raw/.sep files reflects the way in which Bungie West chose to store levels in memory. So when we read the data in the files with a hex editor, we can see eccentricities such as blank space and garbage data that represent various RAM contents from the developer's PC such as padding and pointers.

Additionally, because the levels were built on Intel-based machines, which use a little-endian architecture, sequences of bytes which represent numbers were written from least-significant to most-significant byte. FourCCs in the data are stored "backwards", such as "13RV" which is meant to be read "VR31", because Bungie defined those four bytes as a 32-bit integer, not a string, causing them to be written to disk in little-endian order.

File limits

  • Max level number: 127
  • Max number of instance files in GameDataFolder: 512 (Windows), 16 (Windows demo, Mac)
  • Max number of simultaneously loaded instance files: 64
  • Max number of instances in a file: 131071
  • Max length of an instance file name: 31
  • Max length of an instance name: 63 (including the 4 character template tag)


Here is a walkthrough of an instance file using the level0_Final.dat in English Windows Oni. Follow along in a hex editor for maximum learnage. Each term will be explained in-depth when we fully consider the related data. First, here is how the file begins:

Offset Type Raw Hex Value Description
0x00 int64 1F 27 DC 33 DF BC 03 00 0x0003BCDF33DC271F Windows instance file total template checksum; Windows demo and Mac retail/demo use 0x0003BCDF23C13061 instead
0x08 int32 31 33 52 56 'VR31' .dat version; OniSplit's .oni files use 'VR32' instead
0x0C int16 40 00 64 size of this header
0x0E int16 14 00 20 size of instance descriptor
0x10 int16 10 00 16 size of template descriptor
0x12 int16 08 00 8 size of name descriptor
0x14 int32 83 24 00 00 9347 instance descriptor count
0x18 int32 D4 1B 00 00 7124 name descriptor count
0x1C int32 38 00 00 00 56 template descriptor count
0x20 int32 A0 BC 03 00 0x03BCA0 data table offset
0x24 int32 A0 35 25 00 2438560 data table size
0x28 int32 40 F2 28 00 0x28F240 name table offset
0x2C int32 04 4F 02 00 151300 name table size
0x30 int32 00 00 00 00 used by OniSplit only: raw table offset
0x34 int32 00 00 00 00 used by OniSplit only: raw table size
0x38 int32 00 00 00 00 unused
0x3C int32 00 00 00 00 unused

The file's total template checksum is the sum of all the template checksums (see "Template descriptors" below). Oni looks at this number in order to validate that it can read this version of the game data format. In practical terms, the total checksum value given for Windows above tells us that this level data is in the .dat/.raw file scheme, and the value given for Mac Oni and the Windows demo tells us that the level data uses the .dat/.raw/.sep file scheme.

The version of the instance file is the format version. Reading it backwards, as discussed under the "Backwards and garbage data" section, we get "VR31", which is probably "version 31". This is the format version of all instance files in all releases of Oni, regardless of file scheme.

The descriptor sizes are the sizes of the instance, template, and name descriptors which are coming up in this file (see breakdowns in later sections). For instance, each instance descriptor will be 0x14, or 20 bytes, in length.

The descriptor counts are the sizes of arrays which are coming up in this file: the instance, name and template descriptors. For instance, the size of the instance descriptor array will be 0x2483, or 9,347 items, in length.

Next we are told the addresses and sizes of the data and name tables in the instance file. The name table simply follows the data table, as you'll see if you add the data table offset plus the data table size, but that doesn't mean the name table offset is redundant; if its start was not 32-bit-aligned, it probably would be moved down to start at the next 32-bit word, but this is unnecessary because it happens to be aligned already.

After this comes four "int"s of zeroes. Empty space like this is common in the data files, and indicates that something stored in memory at this relative position was not written to disk (probably pointers, or sometimes a space reserved for possible future use in a resource type).

That concludes the header of the instance file. Immediately after this header, we find the instance descriptors array.

Instance descriptors

The instance descriptor array tells Oni where to find the data and the name of every instance (resource) indexed by the .dat file. The descriptors start at 0x40 in the .dat file, but below is a descriptor found at 0x017B50 in the file which makes a better example. In the table below, we use offsets relative to the start of this descriptor.

Offset Type Raw Hex Value Description
0x00 tag 54 42 55 53 'SUBT' template tag
0x04 int32 C8 30 22 00 0x2230C8 data offset (relative to data table)
0x08 int32 01 CB 00 00 0xCB01 name offset (relative to name table)
0x0C int32 C0 09 00 00 2496 data size
0x10 int32 00 00 00 00 0 flags; possible values:
0x01 00 00 00 - unnamed
0x02 00 00 00 - empty
0x04 00 00 00 - never used; appears to mean "big-endian" data
0x08 00 00 00 - shared

This descriptor tells us that a resource of type SUBT (a subtitle file for Oni; there are only two of these, one containing all speech subtitles, and one for help messages) has data that can be found 0x2230C8 bytes into the data table, which we learned from the file header starts at 0x03BCA0. Its name can be found 0xCB01 bytes into the name table that starts, according to the file header, at 0x28F240. The data's size is 0x09C0, or 2,496, bytes. The flags "unnamed" and "empty" require special explanation.

Unnamed and empty resources

You'll notice that the level file header lists fewer names (7,124) than instances (9,347). That's because there are 3 types of instance:

  • Unnamed and not empty - they are only referenced by other instances in the same file, generally as child data (e.g., 3D geometry elements like ABNA are "contained" by AKEV, a level's environment).
  • Named and not empty - they can be referenced by other instances in any file and the engine can use their name or template tag to find them.
  • Named and empty - "empty" instances are used in level-specific instance files (i.e. not in level0_Final.dat) to associate an instance ID with a name. For every empty resource, there's another one with a matching name in level0_Final.dat that has data in it. The empty resource in the instance file is (usually) looked up by ID, then the engine searches all the loaded files for a non-empty instance with the same name, causing it to find the actual file in the global data in level0_Final.dat.

Peeking at instance name

Before we talk about the name table in depth, we can peek ahead at the name of this resource using the offset we've just been given. Let's add the offset 0xCB01 to 0x28F240, the file header's address for the name table. This gives us the address 0x29BD41. There we find the string "SUBTsubtitles".

Peeking at instance data

The actual subtitle data should be found by adding the offset 0x2230C8 to 0x03BCA0, the file header's address for the data table, to get 0x25ED68. We're going to leave the full details of the data table for later, but below is the data you should actually see for the English Oni SUBT file at this address. You have to consult the SUBT page to know how to read this data.

Offset Type Raw Hex Value Description
0x08 char[16] AD DE dead unused
0x18 offset 80 44 44 01 0x01444480 raw file data address
0x1C int32 61 02 00 00 609 array size

After padding of 16 unused bytes, we find that, instead of data, there's an address of the actual data: it's in the level's raw file. Open level0_Final.raw and jump to address 0x01444480, and you should see "01_01_01 Griffin: Give me another reading.", and the rest of some very familiar dialogue continuing from there.

The array size of 609 tells the part of the engine that reads SUBT data to expect a chunk of 609 subtitled lines of dialogue.

Name descriptors

The name descriptor array starts immediately after the instance descriptors array. To find the end of the instance descriptors, we can simply take the size of an instance descriptor, 20 bytes, and multiply it by the number of instance descriptors in the file header. In this case, that means 20 * 9347 = 186940, or 0x02DA3C. Adding that to 0x40 (the start of the instance descriptors) takes us to address 0x02DA7C. Voila, the start of the name descriptors.

The name descriptor array stores the numbers of all named instances in alphabetical order. This allows the engine to do a binary search to quickly find instances by name. It is also used when finding instances by type. However the addresses of these instances in memory cannot be known until the file is loaded into RAM, so a space of 32 bits is reserved for that runtime pointer.

Offset Type Raw Hex Value Description
0x00 int32 15 16 00 00 5653 instance number
0x04 int32 60 2C 1C 0E (garbage) runtime: pointer to instance name

Template descriptors

Likewise, the template descriptor array starts directly after the name descriptors. Since name descriptors are 8 bytes, 8 * 7124 (taken from the header) = 56992, or 0xDEA0, and adding that to the name descriptor array's start address (0x02DA7C) gives us 0x03B91C as the start of the template descriptors.

The template descriptor array contains information about all templates (that is, resource types, AKA tags), used in the file (56 in this case, as we learned from the file header). Any resource occurring in this instance file has to have its type listed here.

Offset Type Raw Hex Value Description
0x00 int64 A0 6D 12 00 00 00 00 00 0x126DA0 template checksum
0x08 tag 41 4E 42 41 'ABNA' template tag
0x0C int32 01 00 00 00 1 number of resources in file that use this template

The template checksum is used to prevent loading of instance files that are not compatible with the current engine version. The tag is the same kind of number-written-as-backwards-ASCII that we discussed in the "Backwards and garbage data" section. The number of resources is self-explanatory.

You might wonder how Oni knows how to read each type of data, such as a SUBT or an ABNA. The simple answer is that this information is hard-coded into Oni. In fact, the information on each instance type, as stored in Oni's code, is actually the real "template". The file data only gives the tag and checksum that refer to a certain template. Which types of data fields are encountered in which order is already known by Oni. These hardcoded templates also tell Oni which parts of the file data are reserved for pointers.

That's because an instance may have pointers to other related instances, but pointers are only valid in memory; they cannot be stored on disk. They must be set when the level data is loaded into memory and the address in RAM has been determined. So one type of data field in Oni's templates is a raw pointer; on Macs and the Windows demo, there is an additional "separate offset" type. The pointer and offset are 32 bits in length, as one must expect since Oni was compiled for 32-bit PCs.

Incidentally, the templates in Oni's code have not just the familiar four-character tags attached to them, but also a descriptive string, e.g. "BSP Tree Node Array". This is the source of the names on the File types page.

Data table

The data table stores all the instance data (or points to its actual location in a raw/separate file). We peeked at this before when we looked at the instance descriptor for SUBTsubtitles.

The start of each instance's record, the ID number, is always 32 byte-aligned. Thus, even though the template descriptors ended at 0x03BC9C, there are four empty bytes here so that the data table can begin at 0x03BCA0, which divides evenly by 32. This alignment also means that the instance-specific data will always be found at an offset like 0x0008, 0x0028, 0x0148 etc.

The instance ID and file ID are not actually part of the instance data, but are considered to be the resource header. The engine always keeps pointers to the start of the type-specific data itself; we saw this before when we jumped to 0x25ED68 and saw the data for the SUBT rather than the header for this data. The instance ID and file ID are accessed using negative offsets when needed (usually to find the name or template tag of an instance, given a pointer to it).

Offset Type Raw Hex Value Description
0x00 res_id 01 00 00 00 0 instance ID
0x04 lev_id 01 00 00 00 0 file ID
0x08 ... ... ... type-specific data...

The instance's ID is computed as:

(instance_descriptor_index << 8) | 1

The 1 allows the engine to know which IDs have already been converted to pointers (an instance pointer will always be 8 byte-aligned, so it will never have the zero bit already set).

The file ID is computed from the name of the instance file. For "_Final" files the file ID is computed as:

(level_number << 25) | 1

Again, the 1 allows the engine to know which file IDs have already been converted to pointers.

As you can see, after the header, the size of the actual instance data can be almost anything. Thus, we cannot compute the end of the data table in any simple way. That's why the instance file header explicitly gives us the address of the name table that comes after this.

By the way, how do we know which resource's data we're looking at in the data table? Let's look at the very first data, at 0x03BCA0. Noting that the first two numbers, the instance and file ID, do not count as data, there must be a resource with a data offset of 0x08, the lowest offset possible into the table. We can find this offset listed right at the start of the instance descriptor array:

Offset Type Raw Hex Value Description
0x00 tag 53 47 4E 4F 'ONGS' template tag
0x04 int32 08 00 00 00 0x08 data offset (relative to data table)
0x08 int32 00 00 00 00 0x00 name offset (relative to name table)
0x0C int32 60 0F 00 00 3936 data size
0x10 int32 00 00 00 00 0 flags

So this tells us that the first data in the data table belongs to the ONGS resource, and that it extends for 3,936 bytes.

Name table

The name table stores all the instance names as C-style strings (terminated by a zero byte). We peeked at this before when we looked at the instance descriptor for SUBTsubtitles.

Offset Type Raw Hex Value Description
0x00 string 53 55 ... 00 "SUBTsubtitles" name string (zero-terminated)

These names can be up to 63 characters long, counting the tag. The instance file concludes with the end of the name table.