: Since initially writing this page I have done a lot more work with
the ASE file format. I have written a yacc/lex based parser that reads
ASE files into a set of C++ objects, and have also made public the Unreal
ASE Converter. You can find some details of the ASE parser here.
solosnake, 2nd March 2005
Please note that this is not an autorised or
definitive analysis of the ASE file format. Instead I have
addressed only the contents absalutely neccessary for creating
and rendering real time 3D scenes, with referance to the DXA file
format. Below is a complete ascii scene exporter output for a
simple square polygon: the data extracted for the DXA file I have
highlighted. The format is very self explanatory.
*COMMENT "AsciiExport Version 2.00 - Mon Feb 12
*INHERIT_POS 0 0 0
*INHERIT_ROT 0 0
*INHERIT_SCL 0 0 0
*TM_ROW0 1.0000 0.0000
*TM_ROW1 0.0000 1.0000 0.0000
*TM_ROW3 0.0000 -35.1807 0.0000
0.0000 -35.1807 0.0000
*TM_ROTAXIS 0.0000 0.0000
*TM_SCALE 1.0000 1.0000
*TM_SCALEAXIS 0.0000 0.0000 0.0000
is the marker for the value of the scenes ambient lighting level,
expressed as RGB floats. This is analogous to DirectX's
D3DRENDERSTATE_AMBIENT setting. The ambient light is by how much
every object in the scene is lit by default.
is followed by an integer, the number of materials in the scene:
note that if there are NO materials this marker is still present,
but followed by a zero. In my example I have used only a single
material. Each new material will be marked by *MATERIAL at its
and MATERIAL_DIFFUSE are
float RGB values which represent what color the material is and
how it interacts with lighting. The ambient and diffuse values
are used in determining the materials apparant colour in a scene.
The resulting colour is calculated using the vertex normal data
(per vertex in DirectX) and the scenes ambient light against the
materials ambient light, and any diffuse lights against the
materials diffuse value. In general these values should be the
same except for special effects.
This is a float RGB colour value which represent what colour the
material reflects or highlights. This value ties in with the
dvPower member of a D3DMATERIAL7. When converting from ASE files
which do not have a POWER value DXAtoASE sets the default dvPower
is the path and name of the bitmap used to texture the object in
the ASE file. Note that DXA files do not copy the path data but
instead only extract the actual texture filename to use. If a
material does not contain a texture, then a DXA file mesh object
will have a texture of NOTEXTURE.
and UVW_V_OFFSET The values
represent the offset of the texture on the on the triangle to be
textured. ASE files and DirectX agree on the meaning of the U
value, using it to offset the texture in the conventional 'x'
direction, to the right as looked at, however they disagree on
the V value. In DirectX displacement by V moves a texture DOWN
whereas in ASE files V represents displacemetn up. DXAtoASE
compensates for this and maps correctly. Below is illustrated the
diference in both sets:
These values represent how many times the triangle face is to be
textured using the texture. Think of the texture as a tile. A
UVW_U_TILING value of 1.0 simply means you want one tile to cover
the whole polygon face (think of a rectangular polygon and a
rectanguler texture). For values greater then 1.0 the texture is
applied that many times, so a value of 2.5 means that your
texture will appear on the polygon face 2.5 times. The values can
also be less then 1.0, eg 0.5 which will stretch half the texture
across the entire face of the rectangle. The U and V specify
tiling in the directions indicated in the graphics above. DirectX
and 3ds max and so ASE files differ in their understanding of U
and V tiling. In 3ds max, textures are always centred and tiled
from the ends away from the centre, so a U value of 2.0 results
in a texture appearing once centred and having one half on either
side. in DirectX, a U tiling of 2.0 will result in the texture
being simply repeated twice across the face. Both effects can be
simulated in the other environment (or corrected) using the U and
V offsets. Again, DXA will correct the discrepancy between ASE
and DirectX. Note also that although both DirectX and 3ds max
allow specification of other forms of tiling, eg mirroring, this
does not seem to be output to the ASE file, and so there is no
way to tell in an ASE file what type of texture wrapping to use.
GEOMOBJECT This marks
the beginning of a new geometric object. Although my example has
only one, there may be (usually is) more of these.
is followed by an integer indicating how many vertices this
GEOMOBJECT has. Essentially this is an array of vertices which
the MESH_FACE_LIST will index into later.
This is followed by the integer number of faces in the object. In
my example, a simple plane square, there is two faces. The number
of faces equals the number of triangles the object is composed
of. It is a good measure of the objects 'size'.
is followed by the integer index number of the vertex, then by
that vertex's x, y and z co-ords. Note that ASE files do not have
a left hand co-ordinates sytem, but use the conventional 'real
world' notation of z being 'up', x increasing rightwards, and y
increasing away from you. DXA files use DirectX's left hand
system, and convert ASE accordingly.
I only understanding fully the first half of this row, but thats
all thats needed for most 3d applications: a row is broken down
number: A: X1 B:X2 C:X3
X2, X3 represent indices into the above vertex arrray. Thus face
0 in my example above has as its first point vertex number 0
which is x = -19.6285 y = -52.9010 z = -16.4621, its second point
is vertex number 1, and its third is vertex 3.
Edges I was contacted by Marc Reilly recently,
who suggested that the values AB, BC and CA may be booleans, and
that they indicate whether an egde is visible or not. I think he
is probably right, as they are related to the edges, and they
seem to be only range from 0 to 1. If anyone knows more, or
better, please feel free to contact me. Thanks Marc!
As might be guessed, this is the number of texture co-ordinates
in this file. This does not have to equal the number of vertex
A texture vertex appears to be the same as a regular vertex, but
in fact most applications will only need the first two values,
which are the U and V values for that point.
is followed by the integer number of texture faces. This should
ALWAYS equal the MESH_NUMFACES value, as objects cannot be
A MESH_TFACE is exactly the same in format as a MESH_FACE except
it indexes into the MESH_TVERTLIST array.
Following this is the breakdown of the objects normal data. For
some reason the ASE here changes its format and instead of having
a array of normals which are indexed into it actually just
produces a verbatim list of the details.
This is the x,y,z vector at right angles to the face it is
associated with. Note that this can be calculated from the vertex
data anyway, plus the fact that DirectX uses vertex normals to
calculate lighting, and we can ignore this data.
vertex normals are specified in the same order that the faces
appear in the face list. The integer number refers to the vertex
to which it is a normal. Note that it does not neccessarily have
to be a true orthonormal vector to its vertex. Objects are made
to appear smoooth by altering their vertex normals so that when
lit the joining faces all meet at same colours, so masking the
ridges. There is usually an option to 'smooth' an object in your
ASE file generator.
This refers back to the *MATERIAL marker, and it is the number of
the material this GEOMOBJECT uses.