OBD:Instance file format

For other files ending in ".dat", see Oni (folder).

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 tools files, named level0_Tools.dat/.raw/.sep, however the retail Oni game application does not load tools files; for the story behind the tools 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 are only loaded when the corresponding level starts and unloaded when it ends.

Terminology

Level data files

The data for each level is found in two files in Windows retail Oni, ending in ".dat" and ".raw". On Macs and in the Windows demo, a third file type ending in ".sep" is used. These two/three files are collectively called level data files.

Instance file

Any file ending in ".dat" found in GameDataFolder/. Instance files are the "main" type of data file in the sense that, when loading a level, Oni reads the instance file first, and this file serves as an index that allows it to find resources which are packed into the binary files.

.dat file

".dat" is a generic suffix originally used by Oni for all kinds of data, including persist.dat. The proper, specific name for the .dat files containing level data, as opposed to the .dat files containing the save-game data, films, etc. is "instance file". That being said, ".dat" has only been used by the community historically to refer to instance files, so you can reasonably assume that's what is meant when you see the suffix. On occasion, ".dat" also refers to the complete set of level data files, .dat/.raw[/.sep].

Binary file

The binary files are basically used for large and unstructured data like textures and sounds. They have no file header, since the instance file serves as the table of contents for them. The only rule about binary files is that all data parts are stored 32 byte-aligned and the first 32 bytes of the file are always zero (reserved to represent null pointers). At load-time, the offsets given in the instance file are converted to pointers to the data in the binary files.

Raw file, .raw

A type of binary file found in both Windows and Mac Oni. On Macs and in the Windows demo these files are much smaller because several resource types store their data in .sep files instead.

Separate file, .sep

By the time that Oni for the Mac was finalized for release, some of the raw data was moved to a third file type which ends in ".sep", short for "separate". You can read about raw and separate files HERE.

Instance, resource

An "instance" is not the same as an "instance file". An instance is an individual resource, such as a texture. This can get confusing when OniSplit is used to split level data into one file per resource, in effect creating thousands of "single-instance instance files".

Template

A template represents a type of resource. Templates are identified with four-letter codes, often called tags, such as "SUBT" for subtitle files.

.oni

Generated by OniSplit, these files are Windows-format .dat files which basically contain a single instance extracted from an instance file, with all the instance data that was contained by the .raw/.sep files appended at the end.

Backwards and garbage data

During development, Oni had in-game editing tools. These tools presented a GUI for things like placing AIs and setting their attributes, editing particles, etc. When a developer saved his work, the contents of the level, stored in RAM, were written directly to disk. The structure of the .dat/.raw/.sep files reflects the way in which Bungie West chose to store levels in memory, and thus when when we read the data in the files with a hex editor, we can see various eccentricities such as blank space and garbage data that represented various RAM contents from the developer's PC.

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, which looks "backwards" from the standpoint of a culture that reads left-to-right. When Macs, which were big-endian at the time due to their PowerPC architecture, read these files, they then had to flip each sequence of bytes in memory before they could be understood.

An exception to this backwards-writing rule is when strings of ASCII characters were written to disk. These are not numbers and thus are not subject to endianness, so they retain their left-to-right order. Now, this may not seem to be the case as you continue reading below. The first two strings of characters which you'll see are "13RV" and "TBUS", which are meant to be read "VR31" and "SUBT". The reason these four-character strings are backwards is that Oni stored them as a 32-bit integer. Any sequence of four characters can be represented as such a number. Writing the integer 1,448,227,633 to disk results in the bytes 0x31, 0x33, 0x52, and 0x56, which produce the ASCII codes for '1', '3', 'R' and 'V' (the computer would have had to be big-endian to be able to naturally write them in the left-to-right order we would prefer to see). This practice of Bungie's provided a combination of convenient storage of a tag in memory as a number, and human-readability when organizing game assets by tag.

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)

Header

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 template checksum; Windows demo and Mac retail/demo use 0x0003BCDF23C13061 instead
0x08	int32	31 33 52 56	'VR31'	.dat version; .oni files use 'VR32' instead
0x0C	int64	40 00 14 00 10 00 08 00	0x0008001000140040	signature
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 template checksum tells us that this level data is in the .dat/.raw file scheme, as opposed to the .dat/.raw/.sep file scheme used by Mac Oni and the Windows demo of Oni.

The version of the instance file is the format version. Reading it backwards, as discussed under "Introduction", we get "VR31", which is probably "version 31". This is the format version of all instance files in all releases of Oni.

The signature is identical in all instance files.

The descriptor counts are the sizes of some arrays which are coming up soon 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 this 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.

There are 3 types of instance descriptors:

• unnamed - they are referenced by other instances in the same file and the engine never reaches them directly
• 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 - the instance data is stored in a different file and they exist only to associate an instance id with a name; when an instance references such an instance id the engine searches all the loaded files for a non empty instance with the same name

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	0x09C0	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 for 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 is 0x09C0, or 2,496, bytes long.

Peeking at instance name

If you want to see the name of this resource, let's look at address 0xCB01 + 0x28F240 (the file header's address for the name table) = 0x29BD41. There we find the string "SUBTsubtitles". The actual subtitle data should be found at the address 0x2230C8 + 0x03BCA0 (the file header's address for the data table) = 0x25ED68. Let's go there now....

Peeking at instance data

For some reason, the addresses we calculate from the descriptor data offsets are all off by eight bytes, so we need to subtract 8 from 0x25ED68 and go to 0x25ED60. Compare what you see here to the documentation for the SUBT type. Below is the data you should actually see for the English Oni SUBT file at this address. Note that we still haven't found the actual subtitle data, because SUBT stores its data in the raw file. The princess is in another castle:

Offset	Type	Raw Hex	Value	Description
0x00	res_id	01 F4 12 00	4852	04852-subtitles.SUBT
0x04	lev_id	01 00 00 00	0	level 0
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

The first two words, or 32-bit sequences, are the standard resource header. The second and third bytes of the first word are the resource ID. The second and third bytes of the second word are the level number where this resource is found.

After a buffer of 16 unused bytes, we find the 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 us that this is 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 level 0 there are 9347 instance descriptors, so 20 * 9347 = 186940. In hex, that's 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: 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). So any resource occurring in this instance file has to have its type listed here.

The template checksum is used to prevent loading of instance files that are not compatible with the current engine version. The number of resources is self-explanatory. Note that "TBUS" has a usage number of 2, which corresponds to what we learned earlier about Oni having only two subtitle files, "SUBTsubtitles" and "SUBTmessages".

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

Template checksum

An instance can have pointers to other related instances, but since pointers are only valid in memory, they cannot be stored on disk. They must be set when the level data is loaded into memory. To be able to do this, the engine must know where pointers are kept in an instance's data, and this is done using "templates". This template info is hard-coded into the game:

• a checksum of the data contained by the template (the checksum algorithm is unknown, but the checksum stored in Oni's code for a given tag must match the one in the template descriptors array for that tag)
• a 4-letter tag used to identify the template (ABNA, ONCC, WMDD, etc.)
• a short description of the data structure, e.g. "BSP Tree Node Array"
• a list of all the instance's data fields and their types (see OBD:Data types)
• other data that appears to be unused, like the size of the fixed part and the size of an array element for data structures that contain variable-length arrays

Data table

The data table stores all the instance data. 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. The engine always keeps pointers to the start of the type-specific data, and 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...

Instance ID

The ID of an instance is computed as:

(instance_descriptor_index << 8) | 1. 

The 1 allows the engine to know which IDs have already been converted to pointers (a instance pointer will always be 8 byte aligned so it can never have the bit 0 set).

File ID

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, the size of a given instance's data can be almost anything. Thus, we cannot compute the end of this table in any simple way. That's why the instance file header explicitly gives us the address of the name table.

By the way, how do we know which resource's data we're looking at in the 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, and knowing that the instance descriptor gives the offset into the data table for the start of each instance's data, that means that there must be a resource with a data offset of 0x08, the lowest offset possible into the table. We can find this 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 {{OBDtr| 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.