ROB File Format

Binary container format. Holds multiple 3D model segments — either embedded inline or as references to external .3DC files.

ROB stores model geometry buckets, not per-instance scene placement transforms. World/object placement comes from scene files (RGM), which reference these models.

Overall Structure

[Header — 20 bytes]
[Segment 0 — 80-byte header + data]
[Segment 1 — 80-byte header + data]
...
[Segment N-1]
[Footer — 4 bytes: "END "]

Some fields use big-endian encoding (a remnant of the original Sega Saturn development), while most use little-endian. Endianness is noted per field.

Header (20 bytes)

Offset	Size	Type	Endian	Name	Description
0x00	4	`[u8; 4]`	—	magic	`"OARC"`; exact expansion unknown.
0x04	4	`u32`	BE	unused_04	Always 4. Unused at runtime; the engine reads the file but never dereferences or tests this field.
0x08	4	`u32`	LE	num_segments	Number of segments.
0x0C	4	`[u8; 4]`	—	magic2	`"OARD"`; exact expansion unknown.
0x10	4	`u32`	BE	payload_size	File size minus 24 (= file size - 20-byte header - 4-byte footer).

Segment Header (80 bytes)

Each segment has a fixed 80-byte header followed by data_size bytes of payload.

Offset	Size	Type	Endian	Name	Description
0x00	4	`u32`	LE	total_size	Data size + 80 (total segment size including header).
0x04	8	`[u8; 8]`	—	name	Segment name, ASCII null-padded. Model name or external `.3DC` filename stem.
0x0C	2	`u16`	LE	segment_type	0 = embedded 3D data, 512 = external `.3DC` reference. See below.
0x0E	2	`u16`	LE	segment_flags	Render mode flags. Only the high byte (at file offset 0x0F) is used at runtime — it becomes a render mode selector. A value of 0 defaults to 0xFF (normal rendering). See Segment Flags below.
0x10	1	`u8`	—	segment_attribs	Per-segment attribute flags. Only this single byte is read at runtime. Bit 1 (0x02) triggers texture pre-loading. Value 0x40 marks special objects (inventory items, shop objects). See Segment Attributes below.
0x11	1	`u8`	—	collision_flags	Copied into static-object runtime collision flags. See Collision flags.
0x12	1	`u8`	—	reserved_12	Zero in all 4,761 installed segments.
0x13	1	`u8`	—	face_count_low	Build tool artifact: `face_count mod 256`.
0x14	4	`u32`	BE	unused_14	Unused — never read at runtime. Most commonly 1 (3,690 segments), but other values exist.
0x18	4	`u32`	—	reserved_18	Always 0.
0x1C	4	`u32`	LE	bbox_extent_x	Bounding box total X extent.
0x20	4	`u32`	LE	bbox_extent_y	Bounding box total Y extent.
0x24	4	`u32`	LE	bbox_extent_z	Bounding box total Z extent.
0x28	4	`u32`	—	reserved_28	Always 0.
0x2C	4	`u32`	—	reserved_2C	Always 0.
0x30	4	`u32`	—	reserved_30	Always 0.
0x34	4	`u32`	LE	bbox_positive_x	Positive X extent from center.
0x38	4	`u32`	LE	bbox_positive_y	Positive Y extent from center.
0x3C	4	`u32`	LE	bbox_positive_z	Positive Z extent from center.
0x40	4	`u32`	LE	bbox_negative_x	Negative X extent from center.
0x44	4	`u32`	LE	bbox_negative_y	Negative Y extent from center.
0x48	4	`u32`	LE	bbox_negative_z	Negative Z extent from center.
0x4C	4	`u32`	LE	data_size	Byte count of the data payload that follows. 0 for external references.

Bounding Box Invariant

bbox_extent == bbox_positive + bbox_negative for all three axes.

For symmetric models: bbox_positive == bbox_negative (center at origin). For asymmetric models, the difference encodes the center offset.

Segment Types

Type	Description
0	Embedded 3D model data. Payload is a complete 3D file (v5.0 format).
256	Embedded 3D model data (menu-specific). Only in `MENU.ROB`. Structurally identical to type 0 — payload is a complete 3D file. Uses version v4.0.
512	External reference. `name` is the `.3DC` filename stem (e.g. `"CYRSA001"` → `CYRSA001.3DC`). `data_size` is 0.

The engine reads only the high byte (file offset 0x0F) of this u16 field. The low byte is always 0x00 and is ignored. The high byte is stored as a render mode selector in the model’s internal data — a value of 0 defaults to 0xFF (standard rendering).

Value	High byte	Names	Render mode
0x0000	0x00 → 0xFF	(all normal)	Standard (default)
0x8C00	0x8C	DR_WA01, DR_WA02, LH_MIRR	Transparency / mirror
0xC800	0xC8	WATERWAT	Water
0x8000	0x80	VR_OHT	Stored as render-mode metadata
0x5A00	0x5A	BEAMA001	Beam / light effect

Segment Attributes (0x10)

A single byte of per-segment attribute flags.

Value	Segments	Meaning
0x00	(all normal)	No special attributes
0x02	PALMTR01–04 (CAVERNS, EXTPALAC, ISLAND)	Texture pre-load trigger (bit 1). Engine calls a texture pre-caching function for all face textures in this segment.
0x40	SS_OBJ01–06, IGRING, IWATER1 (shop items, inventory)	Special object flag (bit 6). Stored as model metadata.

In the Glide renderer, bit 0 (0x01) selects point minification and magnification for queued model draws. When clear, both use bilinear filtering. Archive loading copies the segment attribute byte into model metadata, and ordinary model submission copies it into the instance draw flags. The queued draw pass restores bilinear filtering when it finishes.

Bit 1 (0x02) also enables chroma-key rejection when binding a model face’s texture. With this bit clear, that binding disables chroma keying. The key comes from the texture’s stored key color. This is separate from the archive loader’s texture pre-loading use of the same bit.

Runtime archive selection

Model lookup searches the active primary archive first, then the active world archive. Within each archive it follows stored segment order and returns the first matching name. It does not search every installed ROB archive. Loading a world archive replaces the previous world archive registry. The world loader takes the configured map filename and replaces its extension with ROB in the configured art directory.

The ISLAND world uses FXART\ISLAND.ROB. Its ordinary in-world registry has no primary archive. The names BARREL, BASKET02, LANTERN4, LANTHOL1, MKCARP1 and MKCRATE1 resolve to this world archive even though other installed archives contain different payloads under the same names.

Collision flags (0x11)

Static object loading copies this byte from the named ROB segment into the instance’s runtime collision flags. In collision candidate selection, bit 0x02 excludes the static instance. Otherwise, bit 0x01 routes it to the separate actor-style candidate list; a clear bit selects the model-face list.

Across 4,761 segments in 31 installed ROB archives, the byte values are:

Value	Count
`0x00`	4,726
`0x01`	28
`0x02`	5
`0x04`	1
`0x08`	1

In ISLAND, PLANT000, PLANT001, and PLANT002 use 0x02; BARREL, BASKET01, and BASKET02 use 0x01. See player collision.

Segment Data

For segment_type == 0 (embedded): the data payload is a complete 3D model file starting with its own 64-byte header. Parse with the standard 3D parser.

For segment_type == 256 (menu-specific embedded): same as type 0 — payload is a complete 3D model file. Parse identically. See MENU.ROB Segments below.

For segment_type == 512 (external reference): no data payload. Load the referenced .3DC file from the asset directory using name as the filename stem. External references are exclusively .3DC (animated models) — static .3D geometry is always embedded inline as type 0 segments, never referenced externally.

MENU.ROB Segments

MENU.ROB is the only ROB file containing type 256 segments. It holds 3D models used for the game’s menu screens.

#	Name	Type	Size	Version	Notes
0	MENUA001	256	79,328	v4.0	Menu character model (also exists as standalone `MENUA001.3DC` in `/fxart`)
1	MB_TABLE	0	886	v5.0	Small prop
2	MB_PG01	256	42,208	v4.0	Menu page model
3	MB_PG02	256	42,208	v4.0	Menu page model (same size as PG01)
4	MB_PG03	256	42,208	v4.0	Menu page model (same size as PG01)
5	SCROLL	0	8,136	v5.0	Scroll decoration prop

The three MB_PG segments have the four-byte version v4.0; the following byte belongs to the vertex count, not the version.

4-byte ASCII marker: "END " (with trailing space). Always present.

External References

UESP: Mod:ROB File Format — high-level ROB structure and historical notes.
RGUnity/redguard-unity RGROBFile.cs — ROB segment parsing.

Redguard Preservation Docs