BCO (File Format)

A BCO contains the track's collision data in Mario Kart: Double Dash!!. It is split into 4 parts, where only 2 are known, and are listed below.

File Header

File header of a BCO file

Offset	Type	Description
0x00	String	File magic. Always will be 0003 in ASCII.
0x04	UInt16	Grid width.
0x06	UInt16	Length of grid.
0x08	Int32	X Start of grid.
0x0C	Int32	Z Start of grid.
0x10	Int32	Grid cell X size.
0x14	Int32	Grid cell Z size.
0x18	Int16	The number of entries in the last section.
0x1A	Int16	Possible padding. Always 0x0000.
0x1C	UInt32	Triangle indices offset.
0x20	UInt32	Triangle list offset.
0x24	UInt32	Vertex list offset.
0x28	UInt32	Material list offset.
0x2C	End of File Header

Triangles

Triangles are parts of the collision format that are formed from 3 vertices. Triangles also have the collision type for the defined triangle. The structure is a 0x24 byte structure defined below.

Structure of a triangle in BCO.

Offset	Type	Description
0x00	Int32	The index of the first point of the triangle, from the vertex list.
0x04	Int32	The index of the second point of the triangle, from the vertex list.
0x08	Int32	The index of the third point of the triangle, from the vertex list.
0x0C	Float	Unknown
0x10	Int16	X Direction of normal vector.
0x12	Int16	Y Direction of normal vector.
0x14	Int16	Z Direction of normal vector.
0x16	UInt16	Collision Flags
0x18	Byte	Table for getting Min/Max X/Z values.
0x19	Byte	Camera Code - relates to the position of the player's view camera. 0x00: Only seen in battle courses, Award, and in the outer quicksand in Dry Dry Desert. 0x01: Most common value. 0x02: "Intense camera mode", seen in Dry Dry Desert, Wario Colosseum, and Rainbow Road. The camera is positioned low behind the kart, closer to the exhaust pipes. 0x03: Only seen in Rainbow Road, in the vertical "road" where karts are airborne after entering the cannon. 0x04: Only seen in Pipe Plaza, in the upper level (the metallic platform). 0x05: Seen in Dry Dry Desert, in the very center of the quicksand, and in Rainbow Road, in the descent after the speedy, spiral uphill.
0x1A	Int16	Neighboring Triangle 1
0x1C	Int16	Neighboring Triangle 2
0x1E	Int16	Neighboring Triangle 3
0x20	Byte	Unknown. Values in the stock courses are: 0x00, 0x01 (only in 0x0A__ dead zones), 0x30, and 0x50. Upper 4 bits: In terms of 100 in-game units. Add Thickness value. Last 4 bits: Sets the triangle as invalid for items.
0x21	Byte	Appears to be a flag. 0x00: Most common value. 0x01: Seen in Daisy Cruiser, in the staircase before the finish line, and in Wario Colosseum, in the oval area with the great jump over the big hole.
0x22	Byte	0x00: Most common value. 0x01: Stagger Code: In dead zones, enables the falling animation. 0x10: Spiral Code: Seen in Wario Colosseum, in parts of one of the spiral sections, and Bowser's Castle, in the spiral uphill inside the castle.
0x23	Byte	ID of the associated GeoSplash object where applicable. Seen in: In wavy dead zones (0x0F__). In the muddy, off-road section in Waluigi Stadium (0x0001).
0x24	End of Section

Vertices

Vertices are sets of 3 floats that form a triangle. Each vertex structure is defined in a 0x0C byte structure below.

Structure of a vertex in BCO.

Offset	Type	Description
0x00	Float	X position of the vertex.
0x04	Float	Y position of the vertex.
0x08	Float	Z position of the vertex.
0x0C	End of Section

Material Table

This is a section with an unknown purpose. It is referred to as the matTable in game code. The number of entries is defined in byte 0x18 in the header. The 0xC byte structure is defined below.

Structure of the unknown section in a BCO.

Offset	Type	Description
0x00	UInt16	Collision flag
0x02	Int16	Sound ID
0x04	UInt32	unknown
0x08	UInt32	Unknown
0x0C	End of Section

Collision Flags

Each triangle face has a collision flag that defines how the face acts when the player interacts with it. This can define whether it's sand, mud, ice, and more.

List of collision flags.

ID	Basic Type	Second Byte	Description	Details (Vanilla examples)	Debug String
0x00__	Road	Particles	Medium offroad	Used for the mud sections in Waluigi Stadium and sand in Luigi Circuit	DIRT
0x01__	Road	Particles	Normal Road	Normal road	ROAD
0x02__	Wall	-	Kart and item wall	-	WALL
0x03__	Road	Particles	Medium offroad	Used for grass in multiple courses	GRASS
0x04__	Road	Particles	Slippery Ice	-	ICE
0x05__	Deadzone	Respawn Point	Horizontal bar deadzone	Used for deadzones on level with the road, like in Mushroom City	RESQ
0x06__	-	-	Mario Circuit grassy wall (possibly)	Should be investigated further	SLIP
0x07__	Boost	Respawn Point (Optional)	Zipper on a ramp	Found in Bowser's Castle and Wario Colosseum	DASHJ
0x08__	Boost	-	Zipper Boost	-	DASHB
0x09__	Boost / Teleportation	Respawn Point	Cannon Boost	Requires a GeoCannon object	CANNON
0x0A__	Deadzone	Respawn Point	Circle deadzone	Usually used in the air, such as in Rainbow Road
0x0B__	Road	Respawn Point	Peach Beach sand	-	BEACH
0x0C__	Road	-	Weak Offroad	Used for yellow Dry Dry Desert sand
0x0D__	Teleportation	Respawn Point	Pipe / Teleportation collision	Used in Peach Beach and Mushroom Bridge pipes
0x0E__	Deadzone	Respawn Point	Sand deadzone	Used in Dry Dry Desert in vanilla	RESQD
0x0F__	Deadzone	Respawn Point	Wavy deadzone	Used for water - in vanilla, requires a GeoSplash object	RESQS
0x10__	Deadzone	Respawn Point	Quicksand Sinkhole	Must have an inner and an outer circle of deadzone triangles - the deadzone is the inner circle	VALLEY
0x11__	Deadzone	Respawn Point	PB sand	Function as a deadzone when interacting with heavy water
0x12__	Wall	Sound	Kart wall - not item wall	-	OUTF
0x13__	Road	Particles	Heavy Offroad	Used for orange Dry Dry Desert sand
0x37__/0x47__	Boost	Respawn Point	Zippers with respawn points	Used on ramps, usually before a gap to ensure a higher jump

Sound Types

Each triangle also has a Sound-Type associated with it that defines how the face sounds when the player interacts with it. These are not part of the material name, but instead set in the obj_sound.txt files.

List of sound types.

ID	Sound	Vanilla examples
0x00	Asphalt / Street	Used for the main road in Luigi Circuit and Baby Park
0x01	Dirt / Gravel	Used for the main road in DK Mountain and Dino Dino Jungle
0x02	Stone / Pavement	Used for the inside of the cave in Dino Dino Jungle and the castle in Bowser's Castle
0x03	Wooden Curb	Used for the curbs in Luigi Circuit and Mario Circuit
0x04	-	-
0x05	Wooden Bridge	Used for the bridges in Dino Dino Jungle and Bowser's Castle
0x06	Ice	Used for the slippery ice and the inside of the cave in Sherbet Land
0x07	Grass	Used in a lot of courses
0x08	Stone Wall	Used in a lot of courses
0x09	Metal Wall	Used in a lot of courses
0x0A	Sand	Used for the medium offroad in Dry Dry Desert
0x0B	Rainbow	Used for the main road in Rainbow Road
0x0C	Metal Grid	Used for the metal grids in Wario Colosseum and Bowser's Castle
0x0D	Mud	Used for the deep Mud in Waluigi Stadium
0x0E	-	-
0x0F	Grass Wall	Used for the hedges in Mario Circuit
0x10	Dirt Wall	Used in a lot of courses
0x11	Wood Wall	Used for the ramp walls on Peach Beach
0x12	-	-
0x13	Small Pipe Wall	Used for the small pipes on Luigi Circuit
0x14	Metal	Used for the main road in Wario Colosseum and the bridge in Mushroom Bridge
0x15	Carpet / Smooth	Used for the carpet in Bowser's Castle and the arrow markings in Wario Colosseum
0x16	Snow	Used for the main road and the offroad in Sherbet Land
0x17	Wood / Parquet	Used for the wooden floors in Daisy Cruiser
0x18	Glass	Used for the glass floors in GameCube and Tilt-a-Kart
0x19	Jelly Wall	Used for the jelly walls in Cookie Land
0x1A	DDJ Logs	Used for the logs in Dino Dino Jungle
0x1B	Big Pipe Wall	Used for the big pipes in Waluigi Stadium (much deeper than 0x13 and features reverb)
0x1C	Silent Sand	Used for the main road in Dry Dry Desert (much quieter than 0x0A)
0xFF	Default Wall	Used for the walls around Deadzones

Tools

Mkdd-collision by Yoshi2

References

Tockdom