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The Unofficial 3DStudio 3DS File Format

The Unofficial 3DStudio 3DSFile Format

Notice

This document is an attempt to document theAutoDesk 3DS file format. This was made difficult in that I don't own or haveaccess to a copy of the program, only to sample files. Fortunately, someoneused AutoDesk's own 3DS file development kit to create a program which dumpsthe contents of a 3DS file into a human readable form - albeit somewhatinaccurately. The codes listed and their names come from that program and havebeen confirmed by testing.

It should be known that the 3DS format is,as far as I know, a proprietary format of AutoDesk and that the format detailsare not widely known or are protected by AutoDesk.

It is not my intent to infringe onAutoDesk's rights, but simply to make a large collection of 3D image filesaccessable to people who do not use 3D Studio - or cannot use it becauseAutoDesk has not chosen to provide a version of 3D Studio for the computer theyuse (ie: The Macintosh in my case).

Warning

This document is not intended to be adefinitive definition of the 3DS format and is not authorised by AutoDesk.While every effort has been made to ensure its accuracy, or at least warn youwhen there's doubt about its accuracy, no guarantee of accuracy in any of itcan be given. Use this document at your own risk.

Document layout and format information

In the following document, chunk nameswhich are in bold mean the chunk format has been determined with certainty.Chunk names which are not bold but have a struct following means that this is aguess but is not substantiated. All others are unknown.

A short is always a two byte integer.

A long is always a four byte integer.

A float is always a four byte IEEE floatingpoint number.

A cstr is a zero byte terminated ASCIIstring without a length.

A char is a single byte integer.

3DS FileFormat

A 3DS file consists of blocks of datacalled chunks. Every chunk starts the same way:

short chunk_id;

long chunk_len;

The chunk_id is a unique code whichidentifies the type of data in this chunk and also may indicate the existenceof subordinate chunks. The chunk_len indicates the length of following data tobe associated with this chunk. Note, this may contain more data than just thischunk. If the length of data is greater than that needed to fill in theinformation for the chunk, additional subordinate chunks are attached to thischunk immediately following any data needed for this chunk, and should beparsed out. These subordinate chunks may themselves contain subordinate chunks.

Unfortunately, there is no indication ofthe length of data which is owned by the current chunk, only the total lengthof data attached to the chunk, which means that the only way to parse outsubordinate chunks is to know the exact format of the owning chunk. On theother hand, if a chunk is unknown, the parsing program can skip the entirechunk and subordinate chunks in one jump.

In the following list, I try when possibleto indicate that a chunk is likely to have subordinate chunks and what kinds ofsubordinate chunks I've seen attached to it.

Another problem lies in cstr names. I'veseen cases where the space used by a name is riddled with fragments of oldnames. It seems that the space reserved for a name is not cleared if a smallername replaces it. If the name is removed, you'll get a zero byte indicating animmediate end of string, followed by an undetermined number of characters andnulls. This seems to happen only when the cstr is at the end of a block of dataand so you can assume that the length of the chunk contains no other subchunks.See viewport_data for an example of this.

0xxxH Group

0000H NULL_CHUNK

0001H Unknownchunk

float ???

0002H M3D_VERSION

short version;

0005H M3D_KFVERSION

0010H COLOR_F

float red, grn, blu;

0011H

COLOR_24

char red, grn, blu;

0012H LIN_COLOR_24

char red, grn, blu;

0013H LIN_COLOR_F

float red, grn, blu;

0030H INT_PERCENTAGE

short percentage;

0031H FLOAT_PERCENTAGE

float percentage;

0100H MASTER_SCALE

float scale;

0995H ChunkType

0996H ChunkUnique

0997H NotChunk

0998H Container

0999H IsChunk

0c3cH C_SXP_SELFI_MASKDATA

1xxxH Group

1100H BIT_MAP

cstr filename;

1101H USE_BIT_MAP

1200H SOLID_BGND;followed by color_f

1201H USE_SOLID_BGND

1300H V_GRADIENT;followed by three color_f: start, mid, end

float midpoint;

1301H USE_V_GRADIENT

1400H LO_SHADOW_BIAS

float bias;

1410H HI_SHADOW_BIAS

1420H SHADOW_MAP_SIZE

short size;

1430H SHADOW_SAMPLES

1440H SHADOW_RANGE

1450H SHADOW_FILTER

float filter;

1460H RAY_BIAS

float bias;

1500H O_CONSTS

float plane_x, plane_y, plane_z;

2xxxH Group

2100H AMBIENT_LIGHT

2200H FOG;followed by color_f, fog_bgnd

float near_plane, near_density;

float far_plane, far_density;

2201H USE_FOG

2210H FOG_BGND

2300H DISTANCE_CUEfollowed by dcue_bgnd

float near_plane, near_density;

float far_plane, far_density;

2301H USE_DISTANCE_CUE

2302H LAYER_FOG

float fog_z_from, fog_z_to;

float fog_density;

short fog_type;

2303H USE_LAYER_FOG

2310H DCUE_BGND

2d2dH SMAGIC

2d3dH LMAGIC

3xxxH Group

3000H DEFAULT_VIEW

3010H VIEW_TOP