View source for TDDD IFF 3-D Rendering Data

= TDDD =

<pre>
FORM TDDD is used by Impulse's Turbo Silver 3.0 for 3D rendering
data.  TDDD stands for &quot;3D data description&quot;.  The files contain
object and (optionally) observer data.

Turbo Silver's successor, &quot;Imagine&quot;, uses an upgraded FORM TDDD
when it reads/writes object data.

Currently, in &quot;standard IFF&quot; terms, a FORM TDDD has only two chunk
types:  an INFO chunk describing observer data;  and an OBJ chunk
describing an object heirarchy.  The INFO chunk appears only in
Turbo Silver's &quot;cell&quot; files, and the OBJ chunk appears in both
&quot;cell&quot; files and &quot;object&quot; files.

The FORM has an (optional) INFO chunk followed by some number of
OBJ chunks.  (Note:  OBJ is followed by a space -- ckID = &quot;OBJ &quot;)

The INFO and OBJ chunks, in turn, are made up of smaller chunks with
the standard IFF structure:  &lt;ID&gt; &lt;data-size&gt; &lt;data&gt;.

The INFO &quot;sub-chunks&quot; are relatively straightforward to interpret.

The OBJ &quot;sub-chunks&quot; support object heirarchies, and are slightly
more difficult to interpret.  Currently, there are 3 types of OBJ
sub-chunks:  an EXTR chunk, describing an &quot;external&quot; object in a
seperate file; a DESC chunk, describing one node of a heirarchy;
and a TOBJ chunk marking the end of a heirarchy chain.  For each
DESC chunk, there must be a corresponding TOBJ chunk.  And an
EXTR chunk is equivalent to a DESC/TOBJ pair.

In Turbo Silver and Imagine, the structure of the object heirarchy
is as follows.  There is a head object, and its (sexist) brothers.
Each brother may have child objects.  The children may have
grandchildren, and so on. The brother nodes are kept in a doubly
linked list, and each node has a (possibly NULL) pointer to a
doubly linked &quot;child&quot; list. The children point to the &quot;grandchildren&quot;
lists, and so on.  (In addition, each node has a &quot;back&quot; pointer to
its parent).

Each of the &quot;head&quot; brothers is written in a seperate OBJ chunk,
along with all its descendants.  The descendant heirarchy is
supported as follows:

    for each node of a doubly linked list,

    1)  A DESC chunk is written, describing its object.
    2)  If it has children, steps 1) to 3) are performed
            for each child.
    3)  A TOBJ chunk is written, marking the end of the children.

For &quot;external&quot; objects, steps 1) to 3) are not performed, but
an EXTR chunk is written instead.  (This means that an external
object cannot have children unless they are stored in the same
&quot;external&quot; file).

The TOBJ sub-chunks have zero size -- and no data.  The DESC
and EXTR sub-chunks are made up of &quot;sub-sub-chunks&quot;, again,
with the standard IFF structure:  &lt;ID&gt; &lt;data-size&gt; &lt;data&gt;.

( &quot;External&quot; objects were used by Turbo Silver to allow a its
&quot;cell&quot; data files to refer to an &quot;object&quot; data file that is
&quot;external&quot; to the cell file.  Imagine abandons the idea of
individual cell files, and deals only in TDDD &quot;object&quot; files.
Currently, Imagine does not support EXTR chunks in TDD files.)

Reader software WILL FOLLOW the standard IFF procedure of
skipping over any un-recognized chunks -- and &quot;sub-chunks&quot;
or &quot;sub-sub-chunks&quot;. The &lt;data-size&gt; field indicates how many
bytes to skip.  In addition it WILL OBSERVE the IFF rule that
an odd &lt;data-size&gt; may appear, in which case the corredponding
&lt;data&gt; field will be padded at the end with one extra byte to
give it an even size.


Now, on with the details.

First, there are several numerical fields appearing in the data,
describing object positions, rotation angles, scaling factors, etc.
They are stored as &quot;32-bit fractional&quot; numbers, such that the true
number is the 32-bit number divided by 65536.  So as an example,
the number 3.14159 is stored as (hexadecimal) $0003243F.  This
allows the data to be independant of any particular floating point
format. And it (actually) is the internal format used in the
&quot;integer&quot; version of Turbo Silver.  Numbers stored in this format
are called as &quot;FRACT&quot;s below.

Second, there are several color (or RGB) fields in the data.
They are always stored as three UBYTEs representing the red,
green and blue components of the color.  Red is always first,
followed by green, and then blue.  For some of the data chunks,
Turbo Silver reads the color field into the 24 LSB's of a
LONGword.  In such cases, the 3 RGB bytes are preceded by a
zero byte in the file.


The following &quot;typedef&quot;s are used below:

typedef LONG    FRACT;                /* 4 bytes */
typedef UBYTE   COLOR[3];             /* 3 bytes */

typedef struct vectors {
    FRACT X;          /* 4 bytes */
    FRACT Y;          /* 4 bytes */
    FRACT Z;          /* 4 bytes */
} VECTOR;             /* 12 bytes total */

typedef struct matrices {
    VECTOR I;         /* 12 bytes */
    VECTOR J;         /* 12 bytes */
    VECTOR K;         /* 12 bytes */
} MATRIX;             /* 36 bytes total */

typedef struct _tform {
    VECTOR r;         /* 12 bytes - position */
    VECTOR a;         /* 12 bytes - x axis */
    VECTOR b;         /* 12 bytes - y axis */
    VECTOR c;         /* 12 bytes - z axis */
    VECTOR s;         /* 12 bytes - size */
} TFORM;              /*  60 bytes total */

The following structure is used in generating animated cells
from a single cell.  It can be attached to an object or to the
camera.  It is also used for Turbo Silver's &quot;extrude along a
path&quot; feature.  (It is ignored &amp; forgotten by Imagine)

typedef struct story {
    UBYTE  Path[18];  /* 18 bytes */
    VECTOR Translate; /* 12 bytes */
    VECTOR Rotate;    /* 12 bytes */
    VECTOR Scale;     /* 12 bytes */
    UWORD  info;      /*  2 bytes */
} STORY;              /* 56 bytes total */

The Path[] name refers to a named object in the cell data.
The path object should be a sequence of points connected
with edges.  The object moves from the first point of the
first edge, to the last point of the last edge.  The edge
ordering is important.  The path is interpolated so that
the object always moves an equal distance in each frame of
the animation.  If there is no path the Path[] field should
be set to zeros.
The Translate vector is not currently used.
The Rotate &quot;vector&quot; specifies rotation angles about the
X, Y, and Z axes.
The Scale vector specfies X,Y, and Z scale factors.
The &quot;info&quot; word is a bunch of bit flags:

    ABS_TRA    0x0001    - translate in world coorinates (not used)
    ABS_ROT    0x0002    - rotation in world coorinates
    ABS_SCL    0x0004    - scaling in world coorinates
    LOC_TRA    0x0010    - translate in local coorinates (not used)
    LOC_ROT    0x0020    - rotation in local coorinates
    LOC_SCL    0x0040    - scaling in local coorinates
    X_ALIGN    0x0100    - (not used)
    Y_ALIGN    0x0200    - align Y axis to path's direction
    Z_ALIGN    0x0400    - (not used)
    FOLLOW_ME  0x1000    - children follow parent on path

DESC sub-sub-chunks
-------------------

NAME - size 18

    BYTE    Name[18];       ; a name for the object.

    Used for camera tracking, specifying story paths, etc.

SHAP - size 4

    WORD    Shape;          ; number indicating object type
    WORD    Lamp;           ; number indicating lamp type

    Lamp numbers are composed of several bit fields:

        Bits 0-1:
        0 - not a lamp
        1 - like sunlight
        2 - like a lamp - intensity falls off with distance.
        3 - unused/reserved

        Bits 2:
                0 - non-shadow-casting light
                4 - shadow-casting light

        Bits 3-4:
        0  - Spherical light source
        8  - Cylindrical light source.
        16 - Conical light source.
        24 - unused/reserved

    Shape numbers are:

        0 - Sphere
        1 - Stencil         ; not supported by Imagine
        2 - Axis            ; custom objects with points/triangles
        3 - Facets          ; illegal - for internal use only
        4 - Surface         ; not supported by Imagine
        5 - Ground

    Spheres have thier radius set by the X size parameter.
    Stencils and surfaces are plane-parallelograms, with one
    point at the object's position vector; one side lying along
    the object's X axis with a length set by the X size; and
    another side starting from the position vector and going
    &quot;Y size&quot; units in the Y direction and &quot;Z size&quot; units in
    the X direction.  A ground object is an infinte plane
    perpendicular to the world Z axis.  Its Z coordinate sets
    its height, and the X and Y coordinates are only relevant
    to the position of the &quot;hot point&quot; used in selecting the
    object in the editor.  Custom objects have points, edges
    and triangles associated with them.  The size fields are
    relevant only for drawing the object axes in the editor.
    Shape number 3 is used internally for triangles of custom
    objects, and should never appear in a data file.

POSI - size 12

    VECTOR  Position;       ; the object's position.

    Legal coordinates are in the range -32768 to 32767 and 65535/65536.
    Currently, the ray-tracer only sees objects in the -1024 to 1024
    range.  Light sources, and the camera may be placed outside that
    range, however.

AXIS - size 36

    VECTOR  XAxis;
    VECTOR  YAxis;
    VECTOR  ZAxis;

    These are direction vectors for the object coordinate system.
    They must be &quot;orthogonal unit vectors&quot; - i.e. the sum of the
    squares of the vevtor components must equal one (or close to it),
    and the vectors must be perpendicular.

SIZE - size 12

    VECTOR  Size;

    See SHAP chunk above.  The sizes are used in a variety of ways
    depending on the object shape.  For custom objects, they are
    the lengths of the coordinate axes drawn in the editor.  If the
    object has its &quot;Quickdraw&quot; flag set, the axes lengths are also
    used to set the size of a rectangular solid that is drawn rather
    than drawing all the points and edges.

PNTS - size 2 + 12 * point count

    UWORD   PCount;         ; point count
    VECTOR  Points[];       ; points

    This chunk has all the points for custom objects.  The are
    refered to by thier position in the array.

EDGE - size 4 + 4 * edge cout

    UWORD   ECount;         ; edge count
    UWORD   Edges[][2];     ; edges

    This chunk contins the edge list for custom objects.
    The Edges[][2] array is pairs of point numbers that
    are connected by the edges.  Edges are refered to by thier
    position in the Edges[] array.

FACE - size 2 + 6 * face count

    UWORD   TCount;         ; face count
    UWORD   Connects[][3];  ; faces

    This chunk contains the triangle (face) list for custom objects.
    The Connects[][3] array is triples of edge numbers that are
    connected by triangles.

PTHD - size 2 + 6 * axis count - Imagine only

    UWORD   ACount;         ; axis count
    TFORM   PData[][3];     ; axis data

    This chunk contains the axis data for Imagine &quot;path&quot; objects.
    The PData array contains a TFORM structure for each point along
    the path.  The &quot;Y size&quot; item for the last point on the path tells
    whether the path is closed or not.  Zero means closed, non-zero
    means open.  Otherwise the Y size field is the distance along
    the path to the next path point/axis.

COLR - size 4
REFL - size 4
TRAN - size 4
SPC1 - size 4 - Imagine only

    BYTE    pad;            ; pad byte - must be zero
    COLOR   col;            ; RGB color

    These are the main object RGB color, and reflection, transmission
    and specularity coefficients.

CLST - size 2 + 3 * count
RLST - size 2 + 3 * count
TLST - size 2 + 3 * count

    UWORD   count;          ; count of colors
    COLOR   colors[];       ; colors

    These are the color, reflection and transmission coefficients
    for each face in custom objects. The count should match the
    face count in the FACE chunk. The ordering corresponds to the
    face order.

TPAR - size 64 - not written by Imagine - see TXT1 below

    FRACT   Params[16];     ; texture parameters

    This is the list of parameters for texture modules when
    texture mapping is used.

TXT1 - variable size - Imagine only

    This chunk contains texture data when texture mapping is used.

    UWORD   Flags;          ; texture flags:
                            ;    1 - TXTR_CHILDREN - apply to child objs
    TFORM   TForm;          ; local coordinates of texture axes.
    FRACT   Params[16];     ; texture parameters
    UBYTE   PFlags[16];     ; parameter flags (currently unused)
    UBYTE   Length;         ; length of texture file name
    UBYTE   Name[Length];   ; texture file name (not NULL terminated)
    UBYTE   pad;            ; (if necessary to make an even length)

BRS1 - variable size - Imagine only (version 1.0)
BRS2 - variable size - Imagine only (version 1.1)

    UWORD   Flags;          ; brush type:
                            ;    0 - Color
                            ;    1 - Reflection
                            ;    2 - Filter
                            ;    3 - Altitude
    UWORD   WFlags;         ; brush wrapping flags:
                            ;    1   WRAP_X        - wrap type
                            ;    2   WRAP_Z        - wrap type
                            ;    4   WRAP_CHILDREN - apply to children
                            ;    8   WRAP_REPEAT   - repeating brush
                            ;    16  WRAP_FLIP     - flip with repeats
    TFORM   TForm;          ; local coordinates of brush axes.
    (UWORD   FullScale;)    ; full scale value
    (UWORD   MaxSeq;)       ; highest number for sequenced brushes
    UBYTE   Length;         ; length of brush file name
    UBYTE   Name[Length];   ; brush file name (not NULL terminated)
    UBYTE   pad;            ; (if necessary to make an even length)

    The FullScale and MaxSeq items are in BRS2 chunks only.

SURF - size 5 - not written by Imagine

    BYTE    SProps[5];      ; object properties

    This chunk contains object (surface) properties used
    by Turbo Silver.

    SProps[0] - PRP_SURFACE ; surface type
                            ;   0 - normal
                            ;   4 - genlock
                            ;   5 - IFF brush
    SProps[1] - PRP_BRUSH   ; brush number (if IFF mapped)
    SProps[2] - PRP_WRAP    ; IFF brush wrapping type
                            ;   0 - no wrapping
                            ;   1 - wrap X
                            ;   2 - wrap Z
                            ;   3 - wrap X and Z
    SProps[3] - PRP_STENCIL ; stencil number for stencil objects
    SProps[4] - PRP_TEXTURE ; texture number if texture mapped

MTTR - size 2 - not written by Imagine - see PRP1 chunk.

    UBYTE   Type;           ; refraction type (0-4)
    UBYTE   Index;          ; custom index of refraction

    This chunk contains refraction data for transparent or
    glossy objects.  If the refraction type is 4, the object
    has a &quot;custom&quot; refractive index stored in the Index field.
    The Index field is 100 * (true index of refraction - 1.00)
    -- so it must be in the range of 1.00 to 3.55.  The
    refraction types is 0-3 specify 0) Air - 1.00, 1) Water - 1.33,
    2) Glass - 1.67 or 3) Crystal 2.00.

SPEC - size 2 - not written by Imagine - see SPC1 above.

    UBYTE   Specularity;    ; range of 0-255
    UBYTE   Hardness;       ; specular exponent (0-31)

    This chunk contains specular information.  The Specularity
    field is the amount of specular reflection -- 0 is none,
    255 is fully specular.  The &quot;specular exponent&quot; controls
    the &quot;tightness&quot; of the specular spots.  A value of zero
    gives broad specular spots and a value of 31 gives smaller
    spots.

PRP0 - size 6 - not written by Imagine

    UBYTE   Props[6];       ; more object properties

    This chunk contains object properties that programs other
    than Turbo Silver might support.

    Props[0] - PRP_BLEND    ; blending factor (0-255)
    Props[1] - PRP_SMOOTH   ; roughness factor
    Props[2] - PRP_SHADE    ; shading on/off flag
    Props[3] - PRP_PHONG    ; phong shading on/off flag
    Props[4] - PRP_GLOSSY   ; glossy on/off flag
    Props[5] - PRP_QUICK    ; Quickdraw on/off flag

    The blending factor controls the amount of dithering used
    on the object - 255 is fully dithered.  
    The roughness factor controls how rough the object should
    appear - 0 is smooth, 255 is max roughness.
    The shading flag is interpreted differently depending on
    whether the object is a light source or not.  For light
    sources, it sets the light to cast shadows or not.  For
    normal objects, if the flag is set, the object is always
    considered as fully lit - i.e. it's color is read directly
    from the object (or IFF brush), and is not affected by light
    sources.
    The phong shading is on by default - a non-zero value turns
    it off.
    The glossy flag sets the object to be glossy or not.  If
    the object is glossy, the &quot;transmit&quot; colors and the index
    of refraction control the amount of &quot;sheen&quot;.  The glossy
    feature is meant to simulate something like a wax coating
    on the object with the specified index of refraction. The
    trasmission coefficients control how much light from the
    object makes it through the wax coating.
    The Quickdraw flag, if set, tells the editor not to draw
    all the points and edges for the object, but to draw a
    rectanglular solid centered at the object position, and
    with sizes detemined by the axis lengths.

PRP1 - size 8 - Imagine only

    UBYTE   IProps[8];       ; more object properties

    This chunk contains object properties that programs other
    than Imagine might support.

    IProps[0] - IPRP_DITHER   ; blending factor (0-255)
    IProps[1] - IPRP_HARD     ; hardness factor (0-255)
    IProps[2] - IPRP_ROUGH    ; roughness factor (0-255)
    IProps[3] - IPRP_SHINY    ; shinyness factor (0-255)
    IProps[4] - IPRP_INDEX    ; index of refraction
    IProps[5] - IPRP_QUICK    ; flag - Quickdraw on/off
    IProps[6] - IPRP_PHONG    ; flag - Phong shading on/off
    IProps[7] - IPRP_GENLOCK  ; flag - Genlock on/off

    The blending factor controls the amount of dithering used
    on the object - 255 is fully dithered.  
    The hardness factor controls how tight the specular spot
    should be - 0 is a big soft spot, 255 is a tight hot spot
    The roughness factor controls how rough the object should
    appear - 0 is smooth, 255 is max roughness.
    The shiny factor in interaction with the object's filter
    values controls how shiny the object appears.  Setting it
    to anything but zero forces the object to be non-transparent
    since then the filter values are used in the shiny (reflection)
    calculations.  A value of 255 means maximum shinyness.

INTS - size 4 - not written by Imagine

    FRACT   Intensity;      ; light intensity

    This is the intensity field for light source objects.
    an intensity of 255 for a sun-like light fully lights
    object surfaces which are perpendicular to the direction
    to the light source.  For lamp-like light sources, the
    necessary intensity will depend on the distance to the light.

INT1 - size 12 - Imagine only

    VECTOR  Intensity;      ; light intensity

    This is like INTS above, but has seperate R, G &amp; B intensities.

STRY - size 56 - not written by Imagine

    STORY   story;          ; a story structure for the object.

    The story structure is described above.

ANID - size 64 - Imagine only

    LONG    Cellno;         ; cell number
    TFORM   TForm;          ; object position/axes/size in that cell.

    For Imagine's &quot;Cycle&quot; objects, within EACH DESC chunk in the
    file - that is, for each object of the group, there will be
    a series of ANID chunks.  The cell number sequences of each
    part of the must agree with the sequence for the head object,
    and the first cell number must be zero.

FORD - size 56 + 12 * PC - Imagine only

    WORD    NumC;           ; number of cross section points
    WORD    NumF;           ; number of slices
    WORD    Flags;          ; orientation flag
    WORD    pad;            ; reserved
    MATRIX  TForm;          ; object rotation/scaling transformation
    VECTOR  Shift;          ; object translation
    VECTOR  Points[PC];     ; &quot;Forms&quot; editor points

    For Imagine's &quot;Forms&quot; objects, the &quot;PNTS&quot; chunk above is not
    written out, but this structure is written instead.  The point
    count is PC = NumC + 4 * NumF.  The object's real points are
    then calculated from these using a proprietary algorithm.
    The tranformation parameters above allow the axes of the
    real object be moved around relative to the &quot;Forms&quot; points.


DESC notes
----------

Again, most of these fields are optional, and defaults are supplied.
However, if there is a FACE chunk, there must also be a CLST chunk,
an RLST chunk and a TLST chunk -- all with matching &quot;count&quot; fields.
The SHAP chunk is not optional. 

Defaults are:  Colors set to (240,240,240); reflection and
transmission coefficients set to zero; illegal shape; no story or
special surface types; position at (0,0,0); axes aligned to the
world axes; size fields all 32.0; intensity at 300; no name;
no points/edges or faces; texture parameters set to zero; refraction
type 0 with index 1.00; specular, hardness and roughness set to zero;
blending at 255; glossy off; phong shading on; not a light source;
not brightly lit;

In Imagine, defaults are the same, but with colors (255,255,255).


INFO sub-chunks
---------------

BRSH - size 82

    WORD    Number;        ; Brush number (between 0 and 7)
    CHAR    Filename[80];  ; IFF ILBM filename

    There may be more than one of these.

STNC - size 82

    Same format as BRSH chunk.

TXTR - size 82

    Same format as BRSH chunk.  The Filename field is the name of
    a code module that can be loaded with LoadSeg().

OBSV - size 28

    VECTOR  Camera;         ; Camera position
    VECTOR  Rotate;         ; Camera rotation angles
    FRACT   Focal;          ; Camera focal length

    This tells where the camera is, how it is aimed, and its
    focal length.  The rotation angles are in degrees, and specify
    rotations around the X, Y, and Z axes.  The camera looks down
    its own Y axis, with the top of the picture in the direction of
    the Z axis.  If the rotation angles are all zero, its axes
    are aligned with the world coordinate axes.  The rotations are
    performed in the order ZXY about the camera axes.  A positive
    angle rotates Y toward Z, Z toward X, and X toward Y for
    rotations about the X, Y, and Z axes respectively.  To
    understand the focal length, imagine a 320 x 200 pixel
    rectangle perpendicular to, and centered on the camera's
    Y axis.  Any objects in the infinite rectangular cone defined
    by the camera position and the 4 corners of the rectangle will
    appear in the picture.

OTRK - size 18

    BYTE    Trackname[18];

    This chunk specifies the name of an object that the camera
    is &quot;tracked&quot; to.  If the name is NULL, the camera doesn't
    track.  Otherwise, if the object is moved inside Turbo Silver,
    the camera will follow it.

OSTR - size 56

    STORY   CStory;         ; a STORY structure for the camera

    The story structure is defined above.

FADE - size 12

    FRACT   FadeAt;         ; distance to start fade
    FRACT   FadeBy;         ; distance of total fade
    BYTE    pad;            ; pad byte - must be zero
    COLOR   FadeTo;         ; RGB color to fade to

SKYC - size 8

    BYTE    pad;            ; pad byte - must be zero
    COLOR   Horizon;        ; horizon color
    BYTE    pad;            ; pad byte - must be zero
    COLOR   Zenith;         ; zenith color

AMBI - size 4

    BYTE    pad;            ; pad byte - must be zero
    COLOR   Ambient;        ; abmient light color

GLB0 - size 8

    BYTE    Props[8];       ; an array of 8 &quot;global properties&quot; used
                            ; by Turbo Silver.

    Props[0] - GLB_EDGING       ; edge level (globals requester)
    Props[1] - GLB_PERTURB      ; perturbance (globals requester)
    Props[2] - GLB_SKY_BLEND    ; sky blending factor (0-255)
    Props[3] - GLB_LENS         ; lens type (see below)
    Props[4] - GLB_FADE         ; flag - Sharp/Fuzzy focus (globals)
    Props[5] - GLB_SIZE         ; &quot;apparant size&quot; (see below)
    Props[6] - GLB_RESOLVE      ; resolve depth (globals requester)
    Props[7] - GLB_EXTRA        ; flag - genlock sky on/off

    The edging and perturbance values control the heuristics in
    ray tracing.  The sky blending factor is zero for no blending,
    and 255 for full blending.  The lens type is a number from 0
    4, corresponding to the boxes in the &quot;camera&quot; requester, and
    correspond to 0) Manual, 1) Wide angle, 2) Normal, 3) Telephoto,
    and 4) Custom.  It is used in setting the camera's focal length
    if the camera is tracked to an object.  The Sharp/Fuzzy flag
    turns the &quot;fade&quot; feature on and off - non-zero means on.
    The &quot;apparant size&quot; parameter is 100 times the &quot;custom size&quot;
    parameter in the camera requester.  And is used to set the
    focal length for a custom lens.  The &quot;resolve depth&quot; controls
    the number of rays the ray tracer will shoot for a single pixel.
    Each reflective/refractive ray increments the depth counter, and
    the count is never allowed to reach the &quot;resolve depth&quot;.  If both
    a reflective and a refractive ray are traced, each ray gets its
    own version of the count - so theoretically, a resolve depth of
    4 could allow much more than 4 rays to be traced.  The &quot;genlock
    sky&quot; flag controls whether the sky will be colored, or set to
    the genlock color (color 0 - black) in the final picture.


All of the INFO sub-chunks are optional, as is the INFO chunk.
Default values are supplied if the chunks are not present.  The
defaults are:  no brushes, stencils, or textures defined; no story
for the camera; horizon and zenith and ambient light colors set
to black; fade color set to (80,80,80);  un-rotated, un-tracked
camera at (-100, -100, 100); and global properties array set to
[30, 0, 0, 0, 0, 100, 8, 0].


EXTR sub-sub-chunks
-------------------

MTRX - size 60

    VECTOR  Translate;      ; translation vector
    VECTOR  Scale;          ; X,Y and Z scaling factors
    MATRIX  Rotate;         ; rotation matrix

    The translation vector is i world coordinates.
    The scaling factors are with respect to local axes.
    The rotation matrix is with respect to the world axes,
    and it should be a &quot;unit matrix&quot;.
    The rotation is such that a rotated axis's X,Y, and Z
    components are the dot products of the MATRIX's I,J,
    and K vectors with the un-rotated axis vector.

LOAD - size 80

    BYTE    Filename[80];   ; the name of the external file

    This chunk contains the name of an external object file.
    The external file should be a FORM TDDD file.  It may contain
    an any number of objects possibly grouped into heirarchy(ies).

Both of these chunks are required.
</pre>