OBD:Instance file format: Difference between revisions

{{OBDtr| 0x0E | uint16  | | 14 00      | 20        | size of instance descriptor }}

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.

|colspan="2" align=left | template tag

|colspan="2" align=left | data offset (relative to data table)

|colspan="2" align=left | name offset (relative to name table)

|colspan="2" align=left | data size

|- align=center valign=top

| 00 00 00 00

| 0

| align=left | flags

| align=left | alt. flags

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. Before we proceed, let's expand upon the '''flags''' field.

These bits have been moved to the upper half of the flags byte (on disk they are cleared altogether in the GDFX data, but this is their location in memory):

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 [[OBD:File types|File types]] page.

{{OBDtr| 0x08 | ...    | | ...        | ... | [[OBD:File_types|type-specific data]]... }}