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XBGMIP Format — High-Detail Streamed LOD (WD1)

Source: blender-io-disrupt addon parser (modules/Watch_Dogs/import_wd.py:391-430), injector (modules/Watch_Dogs/inject_wd.py:166-376), verified byte-exact on helicopter_01.high.xbgmip.

Purpose​

WD1 vehicles and some clothing meshes use streamed LOD — the .xbg file contains lower-detail LODs, while the highest-detail LOD0 lives in a companion .high.xbgmip file. The game streams from the xbgmip as the player approaches. Path is embedded in the XBG's GeomMips section; the file sits next to the .xbg with .high.xbgmip suffix.

File Layout​

Offset Size Field
------ ---- -----
 0 4 magic 'PIMG' (0x50494D47)
 4 4 version u32 = 1
 8 4 reserved u32 = 0
12 4 n_buffers u32 = 1 (always single-buffer)
16 4 vsize u32 = vertex data size in bytes
20 vsize vertex_data packed vertex block
20+v 4 isize u32 = index data size in bytes
24+v isize index_data packed u16 index block

Total file size = 20 + vsize + 4 + isize

All fields are little-endian.

Fields​

FieldTypeDescription
magicchar[4]Always PIMG. Identifies the format.
versionu32Format version. Known: 1.
reservedu32Always 0. Purpose unknown.
n_buffersu32Number of vertex/index buffer pairs. Always 1 in observed files.
vsizeu32Byte length of vertex_data.
vertex_datau8[vsize]Packed vertex data. Layout matches the XBG LOD0 vertex format (stride, format, drawcall offsets from the parent XBG).
isizeu32Byte length of index_data.
index_datau16[isize/2]Triangle strip/fan indices. Same format as XBG index buffers.

Vertex Data​

The vertex_data block uses the same vertex format as the parent XBG's LOD0 drawcalls — same stride, same attribute layout (position, normal, UV, tangent, etc.). The injector patches this block byte-for-byte when modifying vertex positions.

Key detail from the injector: vertex data offset within the buffer is dc['vb_offset'] (drawcall vertex buffer offset from the XBG mesh table). The xbgmip buffer is treated as buffer[0] in the LOD system.

Index Data​

u16 index buffer. Same format as XBG index buffers — indices into the vertex data. The injector re-encodes these when vertex counts change.

Relationship to XBG​

vehicle.xbg ← contains LOD1, LOD2, ... (lower detail)
vehicle.high.xbgmip ← contains LOD0 (highest detail, streamed)

The XBG's GeomMips section lists LODs. When skip >= 1 (meaning the XBG is missing LOD0), the parser looks for <base>.high.xbgmip and prepends it to the buffer list, restoring LOD0 as buffer[0].

Injector Behavior​

The blender-io-disrupt injector (inject_wd.py) patches xbgmip files alongside the XBG:

  1. Reads the companion .high.xbgmip as a bytearray
  2. Patches vertex data in-place (same offset/stride as the XBG's LOD0 drawcalls)
  3. If vertex count changes, calls _maybe_expand_bounds() to resize the buffer sections (shifts index data, updates vsize/isize header fields)
  4. Writes the patched buffer to <out_base>.high.xbgmip next to the output XBG

Important: Without patching the xbgmip, the game streams the pristine hi-res copy over your edit as you approach — the "my edit reverted" bug.

Workaround (No Reverse Engineering Needed)​

FrankMK04's workaround avoids understanding the format entirely:

  1. Delete the xbgmip hash from the XBG file (hex edit)
  2. Replace high.xbgmip with your modified XBG (renamed to .high.xbgmip)
  3. Game cannot find the original high-res, so it uses your modified XBG as LOD0
  4. Original collision detection is retained

Examples​

Observed file: helicopter_01.high.xbgmip (verified byte-exact parse)

Offset 0: 50 49 4D 47 PIMG
Offset 4: 01 00 00 00 version = 1
Offset 8: 00 00 00 00 reserved = 0
Offset 12: 01 00 00 00 n_buffers = 1
Offset 16: [vsize] vertex data size
Offset 20: [vsize bytes] vertex data
Offset 20+v: [isize] index data size
Offset 24+v: [isize bytes] index data

See Also​