Daggerfall Mod:ARCH3D.BSA

ARCH3D.BSA is a NumberRecord (0x0200) BSA file, containing 10251 (0x280B) records. Each record describes a single 3D object/mesh.

3D Object Records

The following description has been tested on all the 3D Objects contained in Arch3D.BSA and appears to be sound. There are two records which have some problems (offsets 0x008B8D58 and 0x013274C6) and don't follow the known format of the other 10249 records. They have a large section of repeating bytes just after the 3D object header and their Data2 section is not the standard. These records could very well be corrupt or not used or of a special, undiscovered, format.

Each BSA record contains the information for one 3D object. Note that each record appears to be similar to the .3D file format used in Battlespire. One difference is that here the .3D files are contained in one big file, while in Battlespire they are in individual files. Records range from 212 to 81394 bytes in size.

A 3D Object Record normally has the following sections:

3D Object Header

Always the first 64 bytes in each 3D Object Record.

This provides offsets to reference the other sections of the record.

PointList

The Point Structures which define the 3D Object Record's geometry are stored here.

PlaneList

The Plane Structures which define the 3D Object Record's geometry are stored here.

Plane Structures refer to elements of the PointList.

NormalList

The Normals for each Plane Structure are stored here.

PlaneDataList

Each Plane Structure implies a 24-byte value, stored here.

ObjectDataList

Each 3D Object Record refers to zero or more ObjectData Structures, stored here.

Two records contain a block of repeating bytes of unknown purpose not referenced within their 3D Object Record Header.

3D Object Header

Each 3D Object is described by a header, which is always the first 64 bytes of the 3D Object Record. This header reports the 3D Object's Version (necessary for interpreting the 3D Object's geometry), number and location of Point structures Plane, etc.

3D Object Record Header Structure

Offset	Type	Name	Description
0-3	String (7-bit ASCII)	Version	Appears to be a version number. The value is not null-terminated. Most of the records report "v2.7", though 135 report "v2.6" and 9 report "v2.5". The "v2.5" records require special care when decoding their geometry (see below).
4-7	Int32	PointCount	The count of Point Structures in the 3D Object's PointList. All records must report at least 3 for their PointCount field. Values should not be negative.
8-11	Int32	PlaneCount	The count of Plane Structures in the 3D Object's PlaneList. All records must report at least 1 for their PlaneCount field. Values should not be negative.
12-15	Int32	Radius	The radius of the mesh, which is the maximum distance of any point in the PointList from the origin (0, 0, 0).
16-23	UInt64	NullValue1	Always 0x0000000000000000.
24-27	Int32	PlaneDataOffset	The offset relative to the 3D Object Record for the 3D Object's PlaneDataList. The position of the PlaneDataList would simply be (RecordStartPosition + PlaneDataOffset).
28-31	Int32	ObjectDataOffset	The offset relative to the 3D Object Record for the 3D Object's ObjectDataList. The position of the ObjectDataList would simply be (RecordStartPosition + ObjectDataOffset).
32-35	Int32	ObjectDataCount	The count of ObjectData elements in the 3D Object Record's ObjectDataList.
36-39	UInt32	Unknown2	Unknown purpose.
40-47	UInt64	NulValue2	Always 0x0000000000000000
48-51	Int32	PointListOffset	The offset relative to the 3D Object Record for the 3D Object's PointList. The position of the PointList would simply be (RecordStartPosition + PointListOffset).
52-55	Int32	NormalListOffset	The offset relative to the 3D Object Record for the 3D Object's NormalList. The position of the NormalList would simply be (RecordStartPosition + NormalListOffset). There is a Normal element for each Plane element, associated by ordinal; that is to say the first Normal is associated with the first Plane.
56-59	UInt32	Unknown3	Unknown purpose.
60-63	Int32	PlaneListOffset	The offset relative to the 3D Object Record for the 3D Object's PlaneList. The position of the PlaneList would simply be (RecordStartPosition + PlaneListOffset).

PointList Section

This section is a contiguous list of PointCount Point structures.

Point Structure

Each Point structure is an Int32 triplet:

PointList Point Structure elements

Offset	Type	Description
0-3	Int32	X
4-7	Int32	Y
8-11	Int32	Z

While the PointList Section is usually adjacent to the Object Header Section, there are two files where the PointList Section begins some distance after the Object Header Section.

PlaneList Section

The PlaneList Section contains PlaneCount Plane Structure elements describing the geometry of the 3D Object Record. This includes the necessary points to describe the geometry, as well as the necessary texture information to display the object.

Each Plane Structure is described by her own header, followed by three or more PlanePoint structures.

Plane Structure elements are contiguous within the PlaneList; that is to say the second Plane Structure immediately follows the first Plane Structure.

Plane Structure Header

Each Plane Structure is described by a header. From this data, one can load the Plane's geometry and texture file information.

The 8-byte header is described as followed:

PlaneHeader

Offset	Type	Name	Description
0	Int8	PlanePointCount	The count of PlanePoint structures describing this Plane's geometry.
1	UInt8	Unknown1	Usually 0x00 for most plane records (about 2% are non-zero). Values range from 0x00 to 0xFF although most are repeating values in the 0x00 to 0x40 range.
2-3	UInt16	Texture	This is the texture information compressed into a bitfield.
4-7	UInt32	Unkown2	Almost always 0x00000000, 0x00010000, 0x00010001, or 0x00010002 and rarely a wide range of other values. Probably two short values.

Texture Structure

The Texture field in the Plane Header is a bitfield containing the FileIndex and ImageIndex fields compressed into a single UInt16. It can be interpreted as follows:

Texture Structure

Bits	Type	Field	Decode	Description
0-6	Int8	ImageIndex	( Texture & 0x7f )	The ordinal index of the image to use in the texture file described by FileIndex.
7-15	Int16	FileIndex	( Texture >> 7 )	The extension of the file to use.

Ex: If ImageIndex were 7, and FileIndex were 214, one would use the eighth image within TEXTURE.214 for the referring Plane Structure.

PlanePoint Structure

Immediately following the Plane Header is a set of PlanePointCount PlanePoint structures. Each structure contains a reference to a Point entry in the Point List Section, as well as the UV coordinates.

The 8-byte structure is as follows:

PlanePoint Structure

Offset	Type	Name	Description
0-3	Int32	PointOffset	This is an offset to a Point Structure within the current 3D Object's PointList. The offset is relative to the 3D Object's PointListOffset field. No values should be negative. This field must be interpreted in context of the 3D Object's Version field.
4-5	Int16	U	The texture UV's U component for the Point referenced.
6-7	Int16	V	The texture UV's V component for the Point referenced.

Interpreting PointOffset

Version	Calculation
2.7	PointListOffset + PointOffset
2.6	PointListOffset + PointOffset
2.5	PointListOffset + ( PointOffset * 3)

See UV Texture Coordinates for interpreting Daggerfall UV coordinate values.

NormalList Section

The NormalList is a PlaneCount set of Point structures, containing the Normals for each Plane structure. Each Point structure element within the NormalList is associated by ordinal to the corresponding Plane Structure; that is to say the first Point structure in the NormalList is the normal for the first Plane structure. Normals are normalized and scaled by 256, so a normal pointing straight down the X axis would be 256 0 0.

PlaneDataList Section

For each Plane structure, there is a corresponding PlaneData structure within the 3D Object Record's PlaneDataList, by ordinal.

The purpose of the data is currently unknown.

PlaneData Structure

Offset	Type	Name	Description
0-23	Int8[ 24 ]	Unknown	Unknown purpose

ObjectDataList Section

There are ObjectDataCount elements of ObjectData Structures within the ObjectDataList. Each ObjectData structure contains zero or more 6-byte ObjectDataValue elements. The ObjectData elements are contiguous; each immediately follows their predecessor.

Each ObjectData Structure is composed of an ObjectDataHeader Structure, and zero or more ObjectDataValue structures. The ObjectDataValue structures, if present, immediately follow the ObjectDataHeader.

ObjectData Structure Header

ObjectDataHeader Structure

Offset	Type	Name	Description
0-15	Int32[ 4 ]	Numbers	Could be a Point Structure and an Int32 magnitude, but in which order?
16-17	Int16	SubrecordCount	The count of the number of ObjectDataValue Structure immediately following.

ObjectDataValue

Each ObjectData Structure contains zero or more ObjectDataValue Structures. An ObjectDataValue structure appears to be a 6-byte field of an unknown purpose.

ObjectDataSubrecord Structure

Offset	Type	Name	Description
0-5	Int8[ 6 ]	Value	Unknown purpose.

Special Objects

The following list of objects (by RecordId) in the ARCH3D file have special mention:

Object 4722 (0x8B8D58)

This v2.6 3D object has a truncated, or different, ObjectDataList which does not conform with the known format.

Object 7614 (0x13274C6)

This v2.7 object has an invalid ObjectDataOffset value (it points to the middle of the PlaneDataList section).

All but 25 of the 10251 records have unique RecordIds. It is not known if the Daggerfall engine loads the first match, or the last match when two or more records collide by RecordId values.