(3ds) 3D Studio File Format

* Subchunks of 4000 - Object Description Block

- first item of Subchunk 4000 is an ASCIIZ string of the objects name.
Remember an object can be a mesh, a light or a camera.

id	Description
4010	unknown
4012	shadow?
4100	Triangular Polygon Object
4600	Light
4700	Camera

* Subchunks of 4100 - Triangular Polygon Object

id	Description
4110	Vertex List
4111	unknown
4120	Points List
4160	Translation Matrix

* 4110 - Vertex List

start	end	size	type	name
0	1	2	short int	Total vertices in object
2	5	4	float	X value
6	9	4	float	Y value
10	13	4	float	Z value
...	...	4	float	bytes 2 .. 13 are repeated [Total vertices in object] times for each vertex.
...	...	4	float
		4	float

* 4111 - unknown

start	end	size	type	name
0	1	2	short int	Total vertices in object?
2	3	2	short int	unknown
...	...	2	short int	bytes 2..3 are repeated for X times as described by short int at start of record.

* 4120 - Points List

start	end	size	type	name
0	1	2	short int	Total polygons in object - numpoly
2	3	2	short int	Point 1
4	5	2	short int	Point 2
6	7	2	short int	Point 3
...	...	2	short int	Repeats 'numpoly' times for each polygon.
...	...	2	short int
...	...	2	short int

These points refer to the corresponding vertex of
the triangular polygon from the vertex list.
Points are organized in a clock-wise order.

* 4160 - Translation Matrix
This structure describes a matrix for the object. It is stored as a 3 X 4 matrix because it is assumed that the right most column is 0,0,0,1

start	end	size	type	name
0	3	4	float	matrix 1,1
4	7	4	float	matrix 1,2
8	11	4	float	matrix 1,3
12	15	4	float	matrix 2,1
16	19	4	float	matrix 2,2
20	23	4	float	matrix 2,3
24	27	4	float	matrix 3,1
28	31	4	float	matrix 3,2
32	35	4	float	matrix 3,3
36	39	4	float	matrix 4,1
40	43	4	float	matrix 4,2
44	47	4	float	matrix 4,3

* 4600 - Light

start	end	size	type	name
0	3	4	float	Light pos X
4	7	4	float	Light pos Y
8	11	4	float	Light pos Z

after this structure check for more chunks.

id	id Description ( full description later )
0010	RGB colour
0011	24 bit Colour
4610	Spot light
4620	Light is off (Boolean)

* 4610 - Spot Light

start	end	size	type	name
0	3	4	float	Target pos X
4	7	4	float	Target pos Y
8	11	4	float	Target pos Z
12	15	4	float	Hotspot
16	19	4	float	Falloff

* 0010 - RGB colour

start	end	size	type	name
0	3	4	float	Red
4	7	4	float	Green
8	11	4	float	Blue

* 0011 - RGB colour - 24 bit

start	end	size	type	name
0	0	1	byte	Red
1	1	1	byte	Green
2	2	1	byte	Blue

* 4700 - Camera
Describes the details of a camera in the scene.

start	end	size	type	name
0	3	4	float	Camera pos X
4	7	4	float	Camera pos Y
8	11	4	float	Camera pos Z
12	15	4	float	Target pos X
16	19	4	float	Target pos Y
20	23	4	float	Target pos Z
24	27	4	float	Camera Bank
28	31	4	float	Camera Lens

* 7001 - unknown chunk
nothing known about this chunk except for its Subchunks. This chunk also exists as a Subchunk in chunk B000 (keyframer info).

id	id Description
7011	unknown
7020	unknown

* B000 - Keyframer Main chunk. Subchunks are

id	id Description
B00A	unknown
7001	unknown
B008	Frames
B009	unknown
B002	Start object description

* B008 - Frame information
simple structure describing frame info.

start	end	size	type	name
0	3	4	integer	start frame
4	7	4	integer	end frame

* B002 - Start of Object info Subchunks

id	id Description
B010	Name & Hierarchy
B011*	Name Dummy object
B013	unknown
B014*	unknown
B015	unknown
B020	Objects pivot point?
B021	unknown
B022	unknown

( * only on dummy objects )

* B010 - Name & hierarchy descriptor

start	end	size	type	name
0	?	?	ASCIIZ	Object name
?	?	?	short int	unknown
?	?	?	short int	unknown
?	?	?	short int	Hierarchy of object

The object hierarchy is a bit complex but works like this. Each object in the scene is given a number to identify its order in the tree. Also each object is ordered in the 3ds file as it would appear in the tree. The root object is given the number -1 (FFFF). As the file is read a counter of the object number is kept.
Is the counter increments the object are children of the previous objects. But when the pattern is broken by a number that will be less than the current counter the hierarchy returns to that level. for example.

object name	hierarchy
A	-1	This example is taken from 50pman.3ds. I would really recommend having a look at one of the example with the hierarchy numbers to help work it out. (if you can describe it any better please let me know. )
B	0
C	1
D	2
E	1
F	4
G	5
H	1
I	7
J	8
K	0
L	10
M	11
N	0
O	13
P	14

Still not done with this chunk yet!
If the object name is $$$DUMMY then it is a dummy object and therefore you should expect a few extra chunks.

* B011 - Dummy objects name.
Names a dummy object. ASCIIZ string.

* B020 - Pivot Point?
The objects pivot point. Not quite sure what the first five floats do yet (ideas?).

start	end	size	type	name
0	3	4	float	unknown
4	7	4	float	unknown
8	11	4	float	unknown
12	15	4	float	unknown
16	19	4	float	unknown
20	23	4	float	Pivot X
24	27	4	float	Pivot Y
28	32	4	float	Pivot Z