Xbox formats¶

The Xbox games on StarLancer's engine, such as Battlestar Galactica, come on discs with the Xbox's own filesystem and executable, and keep their textures in the Xbox's order. The code is in src/formats/xbox/.

sltool cd ls <image>              # every file
sltool cd extract <image> <dir>   # copy everything off

Discs¶

An Xbox disc holds an XDVDFS volume of 2048-byte sectors. An image that extract-xiso writes holds the volume alone, which sltool cd reads. Not supported: a whole disc's image, which holds more than the game's volume (#1019). The volume descriptor is at the volume's sector 32:

Offset	Size	Field
0	20	`MICROSOFTXBOXMEDIA`
20	4	The root directory's first sector
24	4	The root directory's size in bytes

A directory is a binary tree of entries sorted by name, each 4-byte aligned, and an empty one holds one entry of 0xFF filler:

Offset	Size	Field
0	2	The left subtree's offset in the directory, in 4-byte units; 0 or `0xFFFF` for none
2	2	The right subtree's offset, likewise
4	4	The first sector of the file or directory
8	4	Its size in bytes
12	1	Attributes: `0x10` for a directory
13	1	The name's length
14		The name

Executables¶

An Xbox executable, default.xbe, starts with a header that places its sections in memory:

Offset	Size	Field
0	4	`XBEH`
`0x104`	4	The base address: the header loads there
`0x11C`	4	The count of sections
`0x120`	4	The address of the section headers

The header's addresses are in memory, from the base address. A section header is 0x38 bytes:

Offset	Size	Field
0	4	Flags
4	4	The section's address in memory
8	4	Its size in memory
12	4	Its offset in the file
16	4	Its size in the file
20	4	The address of its name

Textures¶

The Xbox's GPU reads a texture's texels swizzled: in Morton order, the bits of a texel's column and its row interleaved into its index, the column's in the even bits and the row's in the odd ones. In a level wider than it is tall, or taller than it is wide, the longer side's bits past the shorter side's stay together above the interleaved ones, so the level is a run of square blocks. A texel at column 3 and row 1 of a 4 by 2 level is at index 7. The Dreamcast's twiddled textures are in Morton order too, with the row's bits first (Dreamcast). xbox/swizzle.zig reads them.