THE AC3D FILE FORMAT (This document last updated 27th March 2003)

The AC3D file format is ascii text and is very simple to parse.  It's also very easy to generate AC3D files from your own data.  This document describes the structure of AC3D files.  Some simple examples are included at the end.
AC3D filenames usually have a '.ac' suffix.  For more information about AC3D, see

an AC3D file has this overall structure:

(Materials - the palette)

An AC3D file always starts with a header line e.g.:


The first four characters are always 'AC3D' the next hex number following
immediately defines the internal version of the file (0xb == 11).  
If the version is later than the program knows about then it will probably
may refuse to load it.  As new versions of the AC3D file format evolve, this number 
is used to make the loading code backwards compatible.

To parse an AC3D file you need something like this:

read the header (AC3Dx)
while not end of file 
    read a line
    check first token on line 
    handle this tokens values (this might involve reading more lines)

This is the basic structure.  %f indicates a floating point value, %d an
integer and %s a string (must be surrounded by quotes " if it contains spaces).
Lines beginning with a '*' indicate an optional section.  The tokens are
case-sensitive.  The indentation is used to show the structure of the file - a
real AC3D file has no indentation.

MATERIAL %s rgb %f %f %f  amb %f %f %f  emis %f %f %f  spec %f %f %f  shi %d  trans %f
	*name %s
        *data %d
	*texture %s
	*texrep %f %f
	*rot %f %f %f  %f %f %f  %f %f %f
	*loc %f %f %f
	*url %s
	*numvert %d
		numvert lines of %f %f %f
	*numsurf %d
		*SURF %d
		*mat %d
		refs %d
                refs lines of %d %f %f
	kids %d

MATERIAL (name) rgb %f %f %f  amb %f %f %f  emis %f %f %f  spec %f %f %f  shi %d  trans %f

single line describing a material.  These are referenced by the "mat" 
token of a surface.  The first "MATERIAL" in the file will be indexed as
zero.  The materials are usually all specified at the start of the file,
imediately after the header.  


Specifies the start of an object. The end of the object section must
be a 'kids' line which indicates how many children objects (may be zero)
follow.  The parameter is the object type - one of:  world, poly,

*name %s

Optional - a name for the object

*data %d

Optional - object data.  Usually the object-data string for an object.
The parameter is an interger which specifies the number of characters
(starting on the next line) to be read.

*texture %s

Optional - default is no texture. the path of the texture bitmap file for the texture of the current object.

*texrep %f %f

Optional - default 1.0,1.0 .  The texture repeat values for the tiling of a texture
on an object's surfaces.

*rot %f %f %f  %f %f %f  %f %f %f

The 3x3 rotation matrix for this objects vertices.  Note that the rotation is relative
to the object's parent i.e. it is not a global rotation matrix.  If this token
is not specified then the default rotation matrix is 1 0 0, 0 1 0, 0 0 1

*loc %f %f %f

The translation of the object.  Effectively the definition of the centre of the object.  This is
relative to the parent - i.e. not a global position.  If this is not found then
the default centre of the object will be 0, 0, 0.

*url %s

The url of an object - default is blank.

*numvert %d
	numvert lines of %f %f %f

The number of vertices in an object.  Parameter specifies the number of 
lins that follow.  If this token is read then you MUST read
that many lines of (%f %f %f) - specifying each vertex point as a local 
coordinate.  Some objects (e.g. groups) may not have a numvert token.

*numsurf %d

The number of surfaces that this object contains.  The parameter specifies
the number of subsections that follow - each one being a different surface

The start of a surface.  The parameter specifies the surface type and flags.
The first 4 bits (flags & 0xF) is the type (0 = polygon, 1 = closedline,
2 = line).  The next four bits (flags >> 4) specify the shading and 
backface.  bit1 = shaded surface bit2 = twosided.

*mat %d
The index to the material that this surface has.

refs %d
    refs lines of %d %f %f

The number of vertices in the surface.  This number indicates the number of lines
following.  Each line contains an index to the vertex and the texture coordinates
for this surface vertex.

kids %d

This is the final token of an object section and it must exist.  If the parameter
is a number > 0 then more objects are recursively loaded as children of the 
current object.

Here is an example file - a simple rectangle (white)

MATERIAL "" rgb 1 1 1  amb 0.2 0.2 0.2  emis 0 0 0  spec 0.5 0.5 0.5  shi 10  trans 0
OBJECT world
kids 1
name "rect"
loc 1 0.5 0
numvert 4
-1 0.5 0
1 0.5 0
1 -0.5 0
-1 -0.5 0
numsurf 1
SURF 0x20
mat 0
refs 4
3 0 0
2 1 0
1 1 1
0 0 1
kids 0

Another example  - an object with 7 vertices (no surfaces, no materials defined)  This is a good way of getting point data into AC3D.  The Vertex->create convex-surface/object can be used on these vertices to 'wrap' a 3d shape around them

numvert 7
-0.83 -0.235 -0.04
-0.63 0.185 -0.04
-0.55 0.235 -0.25
-0.33 0.235 0.29
0.09 0.235 -0.29
0.33 -0.195 -0.04
0.83 0.005 -0.04
kids 0

If you write a loader then you least you need is code to handle the object 
token, and the objects numvert/vertice and numsurf/sufaces - esentially
the geometry of the model.

You can ignore any line that starts with a token other than these e,g textures,
rotation, location etc.

Last revision 27/03/03 ac - removed old email address