Object Files
October 23, 2000
This document describes the LWO2 file format for 3D objects used by LightWave. The LWO2
format is new for LightWave 6.0. Also see the Object File
Examples supplement.
Introduction
The data in LightWave 3D object files comprise the points, polygons and surfaces that
describe the geometry and appearance of an object. "Polygons" here means any of
several geometric elements (faces, curves or patches, for example) defined by an ordered
list of points, and "surfaces" refers to the collection of attributes, sometimes
called materials, that define the visual surface properties of polygons.
Object files can contain multiple layers, or parts, and each part can be a single
connected mesh or several disjoint meshes. They may also contain one or more surface
definitions with no points or polygons at all. Surface definitions can include references
to other files (images, for example), plug-ins, and envelopes containing parameter values
that vary over time.
This document outlines the object file format and provides a detailed reference for
each of the components. The component descriptions include both a regular expression
defining the syntax and a discussion of the contents. See also the Examples supplement, a more conversational introduction to
the format that includes annotated listings of file contents as well as several sample
files.
Data Types
The atomic, or lowest-level, types used in object files are listed below. All of these
are written in a byte order variously called big-endian, Motorola, or network order, with
the most significant byte written first. The shorthand names (I2, F4,
etc.) will be used throughout this document.
- ID Tag
- ID4
An ID tag is a sequence of 4 bytes containing 7-bit ASCII values, usually upper-case
printable characters. These tags are used to identify the data that follows. FORM,
SURF, POLS, and LWO2 are all examples of ID tags. ID tags can
be interpreted as unsigned integers for comparison purposes.
Signed Integer
- I1, I2, I4
- Unsigned Integer
- U1, U2, U4
Integers can be signed or unsigned and 1, 2 or 4 bytes in length. Signed integers are
two's complement.
Float
- F4
4-byte IEEE floating-point values.
String
- S0
Names or other character strings are written as a series of ASCII character values
followed by a zero (or null) byte. If the length of the string including the null
terminating byte is odd, an extra null is added so that the data that follows will begin
on an even byte boundary.
Several useful composite datatypes are built from these fundamental types.
- Variable-length Index
- VX ::= index[U2] | (index + 0xFF000000)[U4]
This is an index into an array of items (points or polygons), or a collection of
items each uniquely identified by an integer (clips or envelopes). A VX is written as a
variable length 2- or 4-byte element. If the index value is less than 65,280 (0xFF00),
then the index is written as an unsigned two-byte integer. Otherwise the index is written
as an unsigned four byte integer with bits 24-31 set. When reading an index, if the first
byte encountered is 255 (0xFF), then the four-byte form is being used and the first byte
should be discarded or masked out.
Color
- COL12 ::= red[F4], green[F4], blue[F4]
A color is written as a triple of floats representing the levels of red, green and
blue. The nominal level range is [0.0, 1.0], but values outside this range are also
possible.
Coordinate
- VEC12 ::= X[F4], Y[F4], Z[F4]
3D coordinates are written as an XYZ vector in floating point format. The values are
distances along the X, Y, and Z axes.
Percentage
- FP4 ::= fraction[F4]
Percentages are written as floats, with 1.0 representing 100%.
Angle
- ANG4 ::= radians[F4]
Angles are specified as floating point values in radians.
Filename
- FNAM0 ::= name[S0]
Filenames are written as strings in a platform-neutral format. For absolute (fully
qualified) paths, the first node represents a disk or similar storage device, and its name
is separated from the rest of the path by a colon. Other nodes in the path are separated
by forward slashes. disk:path/file is an absolute path, and path/subpath/file
is a relative path.
Chunks
The object file format is derived from the metaformat for binary files described in
"EA IFF 85 Standard for Interchange Format Files." The basic structural element in an IFF file is the chunk. A
chunk consists of an ID tag, a size, and size bytes of data. If the size is odd,
the chunk is followed by a 0 pad byte, so that the next chunk begins on an even byte
boundary. (The pad byte isn't counted in the size.)
CHUNK ::= tag[ID4], length[U4],
data[...], pad[U1] ?
Within some chunks, object files use subchunks, which
are just like chunks except that the size is a 2-byte integer.
SUB-CHUNK ::= tag[ID4], length[U2],
data[...], pad[U1] ?
In this document, chunks will be written as a chunk ID followed by
a data description inside curly brackets: ID-tag { data }. Given
this notation, we can say formally that an object file is a FORM chunk of type LWO2.
file ::= FORM { 'LWO2'[ID4], data[CHUNK]
* }
Informally, object files start with the four bytes "FORM" followed
by a four-byte integer giving the length of the file (minus 8) and the four byte ID "LWO2".
The remainder of the data is a collection of chunks, some of which will contain subchunks.
To be read, IFF files must be parsed. The order in which chunks can occur in a
file isn't fixed. Some chunks, however, contain data that depends on the contents of other
chunks, and this fixes a relative order for the chunks involved. Chunks and
subchunks also depend on context for their meaning. The CHAN subchunk in an
envelope chunk isn't the same thing as the CHAN subchunk in a surface block. And
you may encounter chunks that aren't defined here, which you should be prepared to skip
gracefully if you don't understand them. You can do this by using the chunk size to seek
to the next chunk.
The following is a list of the defined chunks that can be found in an object file. Full
descriptions of the contents of ENVL, CLIP and SURF chunks are
deferred to sections that follow the chunk list and comprise the remainder of this
document.
- Layer
- LAYR { number[U2], flags[U2], pivot[VEC12], name[S0], parent[U2] ?
}
Signals the start of a new layer. All the data chunks which follow will
be included in this layer until another layer chunk is encountered. If data is encountered
before a layer chunk, it goes into an arbitrary layer. If the least significant bit of flags
is set, the layer is hidden. The parent index indicates the default parent for this layer
and can be -1 or missing to indicate no parent.
- Point List
- PNTS { point-location[VEC12] * }
Lists
(x, y, z) coordinate triples for a set of points. The number of
points in the chunk is just the chunk size divided by 12. The PNTS chunk must
precede the POLS, VMAP and VMAD chunks that refer to it. These chunks list points using a
0-based index into PNTS.
The LightWave coordinate system is left-handed, with +X to the right or east, +Y
upward, and +Z forward or north. Object files don't contain explicit units, but by
convention the unit is meters. Coordinates in PNTS are relative to the pivot
point of the layer.
- Vertex Mapping
- VMAP { type[ID4], dimension[U2],
name[S0],
( vert[VX], value[F4] # dimension )* }Associates
a set of floating-point vectors with a set of points. VMAPs begin with a type, a
dimension (vector length) and a name. These are followed by a list of vertex/vector pairs.
The vertex is given as an index into the most recent PNTS
chunk, in VX format. The vector contains dimension
floating-point values. There can be any number of these chunks, but they should all have
different types or names.
Some common type codes are
- PICK
- Selection set. This is a VMAP of dimension 0 that marks points for quick
selection by name during modeling. It has no effect on the geometry of the object.
- WGHT
- Weight maps have a dimension of 1 and are generally used to alter the influence of
deformers such as bones. Weights can be positive or negative, and the default weight for
unmapped vertices is 0.0.
- MNVW
- Subpatch weight maps affect the shape of geometry created by subdivision patching.
- TXUV
- UV texture maps have a dimension of 2.
- RGB, RGBA
- Color maps, with a dimension of 3 or 4.
- MORF
- These contain vertex displacement deltas.
- SPOT
- These contain absolute vertex displacements (alternative vertex positions).
Other widely used map types will almost certainly appear in the future.
- Polygon List
- POLS { type[ID4], ( numvert+flags[U2],
vert[VX] # numvert )* }
A list of polygons for the
current layer. Possible polygon types include:
- FACE
- "Regular" polygons, the most common.
- CURV
- Catmull-Rom splines. These are used during modeling and are currently ignored by the
renderer.
- PTCH
- Subdivision patches. The POLS chunk contains the definition of the control cage
polygons, and the patch is created by subdividing these polygons. The renderable geometry
that results from subdivision is determined interactively by the user through settings
within LightWave. The subdivision method is undocumented.
- MBAL
- Metaballs. These are single-point polygons. The points are associated with a VMAP of type MBAL that contains the radius of
influence of each metaball. The renderable polygonal surface constructed from a set of
metaballs is inferred as an isosurface on a scalar field derived from the sum of the
influences of all of the metaball points.
- BONE
- Line segments representing the object's skeleton. These are converted to bones for
deformation during rendering.
Each polygon is defined by a vertex count followed by a list of indexes into the most
recent PNTS chunk. The maximum number of vertices is 1023.
The 6 high-order bits of the vertex count are flag bits with different meanings for each
polygon type. (Currently only two flags are defined: the low two bits are continuity
control point toggles for CURV polygons. Other flags may be defined in the
future.) When reading POLS, remember to mask out the flags to obtain numverts.
When writing POLS, the vertex list for each polygon should begin at a convex
vertex and proceed clockwise as seen from the visible side of the polygon. LightWave
polygons are single-sided (although double-sidedness is a possible
surface property), and the normal is defined as the cross product of the first and last
edges.
- Tag Strings
- TAGS { tag-string[S0] * }
Lists the tag
strings that can be associated with polygons by the PTAG
chunk.
- Polygon Tag Mapping
- PTAG { type[ID4], ( poly[VX], tag[U2] )* }
Associates tags of a given type with polygons in
the most recent POLS chunk. The most common polygon tag
types are
- SURF
- The surface assigned to the polygon. The actual surface attributes are found by matching
the name in the TAGS chunk with the name in a SURF chunk.
- PART
- The part the polygon belongs to. Parts are named groups of polygons analogous to point
selection sets (but a polygon can belong to only one part).
- SMGP
- The smoothing group the polygon belongs to. Shading is only interpolated within a
smoothing group, not across groups.
The polygon is identified by an index into the previous POLS
chunk, and the tag is given by an index into the previous TAGS
chunk. Not all polygons will have a value for every tag type. The behavior for polygons
lacking a given tag depends on the type.
- Discontinuous Vertex Mapping
- VMAD { type[ID4], dimension[U2],
name[S0],
( vert[VX], poly[VX], value[F4]
# dimension )* } (Introduced with LightWave 6.1.) Associates a set of
floating-point vectors with the vertices of specific polygons. VMADs are similar
to VMAPs, but they assign vectors to polygon vertices
rather than points. For a given mapping, a VMAP always
assigns only one vector to a point, while a VMAD can assign as many vectors to a
point as there are polygons sharing the point.
The motivation for VMADs is the problem of seams in UV texture mapping. If a
UV map is topologically equivalent to a cylinder or a sphere, a seam is formed where the
opposite edges of the map meet. Interpolation of UV coordinates across this discontinuity
is aesthetically and mathematically incorrect. The VMAD substitutes an equivalent
mapping that interpolates correctly. It only needs to do this for polygons in which the
seam lies.
VMAD chunks are paired with VMAPs of the same
name, if they exist. The vector values in the VMAD will then replace those in the
corresponding VMAP, but only for calculations involving the
specified polygons. When the same points are used for calculations on polygons not
specified in the VMAD, the VMAP values are used.
VMADs need not be associated with a VMAP. They
can also be used simply to define a (discontinuous) per-polygon mapping. But not all
mapping types are valid for VMADs, since for some types it makes no sense for
points to have more than one map value. TXUV, RGB, RGBA and WGHT
types are supported for VMADs, for example, while MORF and SPOT
are not. VMADs of unsupported types are preserved but never evaluated.
- Envelope Definition
- ENVL { index[VX], attributes[SUB-CHUNK] * }
An array of keys. Each ENVL
chunk defines the value of a single parameter channel as a function of time. The index is
used to identify this envelope uniquely and can have any non-zero value less than
0x1000000. Following the index is a collection of subchunks that describe the envelope.
These are documented below, in the Envelope Subchunks section.
- Image or Image Sequence
- CLIP { index[U4], attributes[SUB-CHUNK] * }
Describes an image or a sequence of
images. Surface definitions specify images by referring to CLIP chunks. The term
"clip" is used to describe these because they can be numbered sequences or
animations as well as stills. The index identifies this clip uniquely and may be any
non-zero value less than 0x1000000. The filename and any image processing modifiers follow
as a variable list of subchunks, which are documented below in the Clip
Subchunks section.
- Surface Definition
- SURF { name[S0], source[S0], attributes[SUB-CHUNK] * }
Describes
the shading attributes of a surface. The name uniquely identifies the surface. This is the
string that's stored in TAGS and referenced by tag index in
PTAG. If the source name is non-null, then this surface is
derived from, or composed with, the source surface. The base attributes of the source
surface can be overridden by this surface, and texture blocks can be added to the source
surface. The material attributes follow as a variable list of subchunks documented below
in the Surface Subchunks section.
- Bounding Box
- BBOX { min[VEC12], max[VEC12]
}
Store the bounding box for the vertex data in a layer. Optional. The min
and max vectors are the lower and upper corners of the bounding box.
- Description Line
- DESC { description-line[S0] }
Store an
object description. Optional. This should be a simple line of upper and lowercase
characters, punctuation and spaces which describes the contents of the object file. There
should be no control characters in this text string and it should generally be kept short.
- Commentary Text
- TEXT { comment[S0] }
Store comments
about the object. Optional. The text is just like the DESC
chunk, but it can be about any subject, it may contain newline characters and it does not
need to be particularly short.
- Thumbnail Icon Image
- ICON { encoding[U2], width[U2], data[U1] * }
An iconic or thumbnail image for the object which
can be used when viewing the file in a browser. Currently the only suported encoding
is 0, meaning uncompressed RGB byte triples. The width is the number of pixels in
each row of the image, and the height (number of rows) is (chunkSize - 4)/width.
This chunk is optional.
Envelope Subchunks
The ENVL chunk contains a series of subchunks describing
the keyframes, intervals and global attributes of a single envelope. Note that the PRE,
KEY and TCB IDs each include a trailing space when written in the file.
- Envelope Type
- TYPE { user-format[U1], type[U1] }
The type subchunk records the format in which the envelope is displayed
to the user and a type code that identifies the components of certain predefined envelope
triples. The user format has no effect on the actual values, only the way they're
presented in LightWave's interface.
- 02 - Float
- 03 - Distance
- 04 - Percent
- 05 - Angle
The predefined envelope types include the following.
- 01, 02, 03 - Position: X, Y, Z
- 04, 05, 06 - Rotation: Heading, Pitch, Bank
- 07, 08, 09 - Scale: X, Y, Z
- 0A, 0B, 0C - Color: R, G, B
- 0D, 0E, 0F - Falloff: X, Y, Z
- Pre-Behavior
- PRE { type[U2] }
The pre-behavior
for an envelope defines the signal value for times before the first key. The type code
selects one of several predefined behaviors.
- 0 - Reset
- Sets the value to 0.0.
- 1 - Constant
- Sets the value to the value at the nearest key.
- 2 - Repeat
- Repeats the interval between the first and last keys (the primary interval).
- 3 - Oscillate
- Like Repeat, but alternating copies of the primary interval are time-reversed.
- 4 - Offset Repeat
- Like Repeat, but offset by the difference between the values of the first and last keys.
- 5 - Linear
- Linearly extrapolates the value based on the tangent at the nearest key.
- Post-Behavior
- POST { type[U2] }
The post-behavior
determines the signal value for times after the last key. The type codes are the same as
for pre-behaviors.
- Keyframe Time and Value
- KEY { time[F4], value[F4] }
The
value of the envelope at the specified time in seconds. The signal value between keyframes
is interpolated. The time of a keyframe isn't restricted to integer frames.
- Interval Interpolation
- SPAN { type[ID4], parameters[F4]
* }
Defines the interpolation between the most recent KEY chunk
and the KEY immediately before it in time. The type identifies the
interpolation algorithm and can be STEP, LINE, TCB
(Kochanek-Bartels), HERM (Hermite), BEZI (1D Bezier) or BEZ2
(2D Bezier). Different parameters are stored for each of these.
- Plug-in Channel Modifiers
- CHAN { server-name[S0], flags[U2],
data[...] }
Channel modifiers can
be associated with an envelope. Each channel chunk contains the name of the plug-in and
some flag bits. Only the first flag bit is defined; if set, the plug-in is disabled. The
data that follows this, if any, is owned by the plug-in.
- Channel Name
- NAME { channel-name[S0] }
An
optional name for the envelope. LightWave itself ignores the names of surface envelopes,
but plug-ins can browse the envelope database by name.
The source code in the sample/envelope directory
of the LightWave plug-in SDK demonstrates interpolation and extrapolation of envelopes and
shows how the contents of the SPAN subchunks define TCB, Bezier and Hermite
curves.
Clip Subchunks
The CLIP chunk contains a series of subchunks describing
a single, possibly time-varying image. The first subchunk has to be one of the source
chunks: STIL, ISEQ, ANIM, XREF or STCC.
- Still Image
- STIL { name[FNAM0] }
The source
is a single still image referenced by a filename in neutral path format.
- Image Sequence
- ISEQ { num-digits[U1], flags[U1],
offset[I2], start[I2], end[I2],
prefix[FNAM0], suffix[S0] }
The
source is a numbered sequence of still image files. Each filename contains a fixed number
of decimal digits that specify a frame number, along with a prefix (the part before the
frame number, which includes the path) and a suffix (the part after the number, typically
a PC-style extension that identifies the file format). The prefix and suffix are the same
for all files in the sequence.
The flags include bits for looping and interlace. The offset is added to the current
frame number to obtain the digits of the filename for the current frame. The start and end
values define the range of frames in the sequence.
- Plug-in Animation
- ANIM { filename[FNAM0], server-name[S0], flags[U2], data[...] }
This
chunk indicates that the source imagery comes from a plug-in animation loader. The loader
is defined by the server name, a flags value, and the server's data.
- Reference (Clone)
- XREF { index[U4], string[S0] }
The source is a copy, or instance, of another clip, given by the index. The string is a
unique name for this instance of the clip.
- Color-cycling Still
- STCC { lo[I2], hi[I2], name[FNAM0] }
A still image with color-cycling is a
source defined by a neutral-format name and cycling parameters. lo and hi
are indexes into the image's color table. Within this range, the color table entries are
shifted over time to cycle the colors in the image. If lo is less than hi,
the colors cycle forward, and if hi is less than lo, they go backwards.
Except for the TIME subchunk, the subchunks after the source subchunk modify
the source image and are applied as filters layered on top of the source image.
- Time
- TIME { start-time[FP4], duration[FP4],
frame-rate[FP4] }
Defines source times for an
animated clip.
- Contrast
- CONT { contrast-delta[FP4], envelope[VX]
}
RGB levels are altered in proportion to their distance from 0.5.
Positive deltas move the levels toward one of the extremes (0.0 or 1.0), while negative
deltas move them toward 0.5. The default is 0.
- Brightness
- BRIT { brightness-delta[FP4], envelope[VX] }
The delta is added to the RGB levels. The default
is 0.
- Saturation
- SATR { saturation-delta[FP4], envelope[VX] }
The saturation of an RGB color is defined as (max
- min)/max, where max and min are the maximum and minimum of the
three RGB levels. This is a measure of the intensity or purity of a color. Positive deltas
turn up the saturation by increasing the max component and decreasing the min
one, and negative deltas have the opposite effect. The default is 0.
- Hue
- HUE { hue-rotation[FP4], envelope[VX]
}
The hue of an RGB color is an angle defined as
r is max: 1/3 (g - b)/(r - min)
g is max: 1/3 (b - r)/(g - min) + 1/3
b is max: 1/3 (r - g)/(b - min) + 2/3
with values shifted into the [0, 1] interval when necessary. The levels between 0 and 1
correspond to angles between 0 and 360 degrees. The hue delta rotates the hue. The default
is 0.
- Gamma Correction
- GAMM { gamma[F4], envelope[VX] }
Gamma correction alters the distribution of light and dark in an image by
raising the RGB levels to a small power. By convention, the gamma is stored as the inverse
of this power. A gamma of 0.0 forces all RGB levels to 0.0. The default is 1.0.
- Negative
- NEGA { enable[U2] }
If non-zero, the
RGB values are inverted, (1.0 - r, 1.0 - g, 1.0 - b), to form a negative of the image.
- Plug-in Image Filters
- IFLT { server-name[S0], flags[U2],
data[...] }
Plug-in image filters can be used to pre-filter an image
before rendering. The filter has to be able to exist outside of the special environment of
rendering in order to work here (it can't depend on functions or data that are only
available during rendering). Filters are given by a server name, an enable flag, and data
bytes that belong to the plug-in.
- Plug-in Pixel Filters
- PFLT { server-name[S0], flags[U2],
data[...] }
Pixel filters may also be used as clip modifiers, and they
are stored and used in a way that is exactly like image filters.
Surface Sub-chunks
The subchunks found in SURF chunks can be divided into
two types. Basic surface parameters are stored in simple subchunks with no nested
subchunks, while texture and shader data is stored in surface blocks containing nested
subchunks.
Basic Surface Parameters
The following surface subchunks define the base characteristics of a surface. These are
the "start" values for the surface, prior to texturing and plug-in shading, and
correspond to the options on the main window of the LightWave Surface Editor. Even if
textures and shaders completely obscure the base appearance of the surface in final
rendering, these settings are still used for previewing and real-time rendering.
- Base Color
- COLR { base-color[COL12], envelope[VX]
}
The base color of the surface, which is the color that lies under all
the other texturing attributes.
- Base Shading Values
- DIFF, LUMI, SPEC, REFL, TRAN, TRNL { intensity[FP4],
envelope[VX] }
The base level of the surface's
diffuse, luminosity, specular, reflection, transparency, or translucency settings. If any
of these subchunks is absent for a surface, a value of zero is assumed.
- Specular Glossiness
- GLOS { glossiness[FP4], envelope[VX]
}
Glossiness controls the falloff of specular highlights. The intensity
of a specular highlight is calculated as cosn a, where a
is the angle between the reflection and view vectors. The power n is the specular
exponent. The GLOS chunk stores a glossiness g as a floating point
fraction related to n by: n = 2(10g + 2). A
glossiness of 20% (0.2) gives a specular exponent of 24, or 16, equivalent to
the "Low" glossiness preset in versions of LightWave prior to 6.0. Likewise 40%
is 64 or "Medium," 60% is 256 or "High," and 80% is 1024 or
"Maximum." The GLOS subchunk is only meaningful when the specularity in
SPEC is non-zero. If GLOS is missing, a value of
40% is assumed.
- Diffuse Sharpness
- SHRP { sharpness[FP4], envelope[VX]
}
Diffuse sharpness models non-Lambertian surfaces. The sharpness refers
to the transition from lit to unlit portions of the surface, where the difference in
diffuse shading is most obvious. For a sharpness of 0.0, diffuse shading of a sphere
produces a linear gradient. A sharpness of 50% (0.5) corresponds to the fixed "Sharp
Terminator" switch in versions of LightWave prior to 6.0. It produces planet-like
shading on a sphere, with a brightly lit day side and a rapid falloff near the day/night
line (the terminator). 100% sharpness is more like the Moon, with no falloff until just
before the terminator.
- Bump Intensity
- BUMP { strength[FP4], envelope[VX]
}
Bump strength scales the height of the bumps in the gradient
calculation. Higher values have the effect of increasing the contrast of the bump shading.
The default value is 1.0.
- Polygon Sidedness
- SIDE { sidedness[U2] }
The sidedness of a polygon can
be 1 for front-only, or 3 for front and back. If missing, single-sided polygons are
assumed.
- Max Smoothing Angle
- SMAN { max-smoothing-angle[ANG4] }
The
maximum angle between adjacent polygons that will be smooth shaded. Shading across edges
at higher angles won't be interpolated (the polygons will appear to meet at a sharp seam).
If this chunk is missing, or if the value is <= 0, then the polygons are not smoothed.
- Reflection Options
- RFOP { reflection-options[U2] }
Reflection
options is a numeric code that describes how reflections are handled for this surface and
is only meaningful if the reflectivity in REFL is non-zero.
- 0 - Backdrop Only
- Only the backdrop is reflected.
- 1 - Raytracing + Backdrop
- Objects in the scene are reflected when raytracing is enabled. Rays that don't intercept
an object are assigned the backdrop color.
- 2 - Spherical Map
- If an image is provided in an RIMG subchunk, the image is
reflected as if it were spherically wrapped around the scene.
- 3 - Raytracing + Spherical Map
- Objects in the scene are reflected when raytracing is enabled. Rays that don't intercept
an object are assigned a color from the image map.
If there is no RFOP subchunk, a value of 0 is assumed.
- Reflection Map Image
- RIMG { image[VX] }
A surface
reflects this image as if it were spherically wrapped around the scene. The RIMG
is only used if the reflection options in RFOP are set to
use an image and the reflectivity of the surface in REFL is
non-zero. The image is the index of a CLIP chunk, or zero
to indicate no image.
- Reflection Map Image Seam Angle
- RSAN { seam-angle[ANG4], envelope[VX]
}
This angle is the heading angle of the reflection map seam. If missing,
a value of zero is assumed.
- Refractive Index
- RIND { refractive-index[F4], envelope[VX]
}
The surface's index of refraction. This is used to bend refraction rays
when raytraced refraction is enabled in the scene. The value is the ratio of the speed of
light in a vacuum to the speed of light in the material (always >= 1.0 in the real
world). The default is 1.0.
- Transparency Options
- TROP { transparency-options[U2] }
The
transparency options are the same as the reflection options in RFOP,
but for refraction.
- Refraction Map Image
- TIMG { image[VX] }
Like RIMG, but for refraction.
- Color Highlights
- CLRH { color-highlights[FP4], envelope[VX] }
Specular highlights are ordinarily the color of
the incident light. Color highlights models the behavior of dialectric and conducting
materials, in which the color of the specular highlight tends to be closer to the color of
the material. A higher color highlight value blends more of the surface color and less of
the incident light color.
- Color Filter
- CLRF { color-filter[FP4], envelope[VX]
}
The color filter percentage determines the amount by which rays passing
through a transparent surface are tinted by the color of the surface.
- Additive Transparency
- ADTR { additive[FP4], envelope[VX]
}
Additive transparency is a simple rendering trick that works
independently of the mechanism associated with the TRAN and
related settings. The color of the surface is added to the color of the scene elements
behind it in a proportion controlled by the additive value.
- Glow Effect
- GLOW { type[U2], intensity[F4],
intensity-envelope[VX], size[F4], size-envelope[VX] }
The glow effect causes a surface to spread and
affect neighboring areas of the image. The type can be 0 for Hastings glow, and 1 for
image convolution. The size and intensity define how large and how strong the effect is.
You may also encounter glow information written in a GVAL subchunk containing
only the intensity and its envelope (the subchunk length is 6).
- Render Outlines
- LINE { flags[U2], ( size[F4],
size-envelope[VX], ( color[COL12],
color-envelope[VX] )? )? }
The line effect draws the
surface as a wireframe of the polygon edges. Currently the only flag defined is an enable
switch in the low bit. The size is the thickness of the lines in pixels, and the color, if
not given, is the base color of the surface. Note that you may encounter LINE
subchunks with no color information (these will have a subchunk length of 8 bytes) and
possibly without size information (subchunk length 2).
- Alpha Mode
- ALPH { mode[U2], value[FP4] }
The
alpha mode defines the alpha channel output options for the surface.
- 0 - Unaffected by Surface
- The surface has no effect on the alpha channel when rendered.
- 1 - Constant Value
- The alpha channel will be written with the constant value following the mode in the
subchunk.
- 2 - Surface Opacity
- The alpha value is derived from surface opacity, which is the default if the ALPH
chunk is missing.
- 3 - Shadow Density
- The alpha value comes from the shadow density.
Surface Blocks
A surface may contain any number of blocks which hold texture layers or
shaders. Each block is defined by a subchunk with the following format.
BLOK { header[SUB-CHUNK],
attributes[SUB-CHUNK] * }
Since this regular expression hides much of the structure of a block, it may be helpful
to visualize a typical texture block in outline form.
- block
- header
- ordinal string
- channel
- enable flag
- opacity...
- texture mapping
- other attributes...
The first subchunk is the header. The subchunk ID specifies the block type, and the
subchunks within the header subchunk define properties that are common to all block types.
The ordinal string defines the sorting order of the block relative to other blocks. The
header is followed by other subchunks specific to each type. For some texture layers, one
of these will be a texture mapping subchunk that defines the mapping from object to
texture space. All of these components are explained in the following sections.
Ordinal Strings
Each BLOK represents a texture layer applied to one of the surface channels,
or a shader plug-in applied to the surface. If more than one layer is applied to a
channel, or more than one shader is applied to the surface, we need to know the evaluation
order of the layers or shaders, or in what order they are "stacked." The ordinal
string defines this order.
Readers can simply compare ordinal strings using the C strcmp function to sort
the BLOKs into the correct order. Writers of LWO2 files need to generate
valid ordinal strings that put the texture layers and shaders in the right order. See the Object Examples supplement for an example function that
generates ordinal strings.
To understand how LightWave uses these, imagine that instead of strings, it used
floating-point fractions as the ordinals. Whenever LightWave needed to insert a new block
between two existing blocks, it would find the new ordinal for the inserted block as the
average of the other two, so that a block inserted between ordinals 0.5 and 0.6 would have
an ordinal of 0.55.
But floating-point ordinals would limit the number of insertions to the (fixed) number
of bits used to represent the mantissa. Ordinal strings are infinite-precision fractions
written in base 255, using the ASCII values 1 to 255 as the digits (0 isn't used, since
it's the special character that marks the end of the string).
Ordinals can't end on a 1, since that would prevent arbitrary insertion of other
blocks. A trailing 1 in this system is like a trailing 0 in decimal, which can lead to
situations like this,
0.5 "\x80"
0.50 "\x80\x01"
where there's no daylight between the two ordinals for inserting another block.
Block Headers
Every block contains a header subchunk.
block-header { ordinal[S0], block-attributes[SUB-CHUNK] * }
The ID of the header subchunk identifies the block type and can be one of the
following.
IMAP - an image map texture
PROC - a procedural texture
GRAD - a gradient texture
SHDR - a shader plug-in
The header contains an ordinal string (described above) and subchunks that are common
to all block types.
- Channel
- CHAN { texture-channel[ID4] }
This is
required in all texture layer blocks and can have a value of COLR,
DIFF, LUMI, SPEC, GLOS, REFL,
TRAN, RIND, TRNL, or BUMP, The texture
layer is applied to the corresponding surface attribute. If present in a shader block,
this value is ignored.
- Enable State
- ENAB { enable[U2] }
True if the
texture layer or shader should be evaluated during rendering. If ENAB is missing,
the block is assumed to be enabled.
- Opacity
- OPAC { type[U2], opacity[FP4],
envelope[VX] }
Opacity is valid only for texture
layers. It specifies how opaque the layer is with respect to the layers before it (beneath
it) on the same channel, or how the layer is combined with the previous layers. The types
can be
0 - Additive
1 - Subtractive
2 - Difference
3 - Multiply
4 - Divide
5 - Alpha
6 - Texture Displacement
Alpha opacity uses the current layer as an alpha channel. The previous layers are
visible where the current layer is white and transparent where the current layer is black.
Texture Displacement distorts the underlying layers. If OPAC is missing, 100%
Additive opacity is assumed.
Texture Mapping
Image map and procedural textures employ the TMAP subchunk to define the
mapping they use to get from object or world coordinate space to texture space.
TMAP { attributes[SUB-CHUNK] *
}
The TMAP subchunk contains a set of attribute chunks which describe the
different aspects of this mapping.
- Position, Orientation and Size
- CNTR, SIZE, ROTA { vector[VEC12], envelope[VX] }
These subchunks each consist of a vector for the
texture's size, center and rotation. The size and center are normal positional vectors in
meters, and the rotation is a vector of heading, pitch and bank in radians. If missing,
the center and rotation are assumed to be zero. The size should always be specified if it
si to be used for any given mapping.
- Reference Object
- OREF { object-name[S0] }
Specifies
a reference object for the texture. The reference object is given by name, and the scene
position, rotation and scale of the object are combined with the previous chunks to
compute the texture mapping. If the object name is "(none)" or OREF is
missing, no reference object is used.
- Falloff
- FALL { type[U2], vector[VEC12],
envelope[VX] }
Texture effects may fall off with
distance from the texture center if this subchunk is present. The vector represents a rate
per unit distance along each axis. The type can be
- 0 - Cubic
- Falloff is linear along all three axes independently.
- 1 - Spherical
- Falloff is proportional to the Euclidean distance from the center.
- 2 - Linear X
3 - Linear Y
4 - Linear Z
- Falloff is linear only along the specified axis. The other two vector components are
ignored.
- Coordinate System
- CSYS { type[U2] }
The coordinate
system can be 0 for object coordinates (the default if the chunk is missing) or 1 for
world coordinates.
Image Maps
Texture blocks with a header type of IMAP are image maps. These use an image
to modulate one of the surface channels. In addition to the basic parameters listed below,
the block may also contain a TMAP chunk.
- Projection Mode
- PROJ { projection-mode[U2] }
The
projection defines how 2D coordinates in the image are transformed into 3D coordinates in
the scene. In the following list of projections, image coordinates are called r
(horizontal) and s (vertical).
- 0 - Planar
- The image is projected on a plane along the major axis (specified in the AXIS subchunk). r and s map to the other
two axes.
- 1 - Cylindrical
- The image is wrapped cylindrically around the major axis. r maps to longitude
(angle around the major axis).
- 2 - Spherical
- The image is wrapped spherically around the major axis. r and s map to
longitude and latitude.
- 3 - Cubic
- Like Planar, but projected along all three axes. The dominant axis of the geometric
normal selects the projection axis for a given surface spot.
- 4 - Front Projection
- The image is projected on the current camera's viewplane. r and s map
to points on the viewplane.
- 5 - UV
- r and s map to points (u, v) defined for the
geometry using a vertex map (identified in the BLOK's VMAP
subchunk).
- Major Axis
- AXIS { texture-axis[U2] }
The major
axis used for planar, cylindrical and spherical projections. The value is 0, 1 or 2 for
the X, Y or Z axis.
- Image Map
- IMAG { texture-image[VX] }
The CLIP
index of the mapped image.
- Image Wrap Options
- WRAP { width-wrap[U2], height-wrap[U2]
}
Specifies how the color of the texture is derived for areas outside the
image.
- 0 - Reset
- Areas outside the image are assumed to be black. The ultimate effect of this depends on
the opacity settings. For an additive texture layer on the color channel, the final color
will come from the preceding layers or from the base color of the surface.
- 1 - Repeat
- The image is repeated or tiled.
- 2 - Mirror
- Like repeat, but alternate tiles are mirror-reversed.
- 3 - Edge
- The color is taken from the image's nearest edge pixel.
If no wrap options are specified, 1 is assumed.
- Image Wrap Amount
- WRPW, WRPH { cycles[FP4], envelope[VX]
}
For cylindrical and spherical projections, these parameters control how
many times the image repeats over each full interval.
- UV Vertex Map
- VMAP { txuv-map-name[S0] }
For UV
projection, which depends on texture coordinates at each vertex, this selects the name of
the TXUV vertex map that contains those coordinates.
- Antialiasing Strength
- AAST { flags[U2], antialising-strength[FP4] }
The low bit of the flags word is an enable flag
for texture antialiasing. The antialiasing strength is proportional to the width of the
sample filter, so larger values sample a larger area of the image.
- Pixel Blending
- PIXB { flags[U2] }
Pixel blending
enlarges the sample filter when it would otherwise be smaller than a single image map
pixel. If the low-order flag bit is set, then pixel blending is enabled.
- STCK
- STCK { value[FP4], envelope[VX]
}
Reserved for future use. The default value is 0.0.
- Texture Amplitude
- TAMP { amplitude[FP4], envelope[VX]
}
Appears in image texture layers applied to the bump channel. Texture
amplitude scales the bump height derived from the pixel values. The default is 1.0.
Procedural Textures
Texture blocks of type PROC are procedural textures that modulate the value of
a surface channel algorithmically.
- Axis
- AXIS { axis[U2] }
If the procedural
has an axis, it may be defined with this chunk using a value of 0, 1 or 2.
- Basic Value
- VALU { value[FP4] # (1, 3) }
Procedurals
are often modulations between the current channel value and another value, given here.
This may be a scalar or a vector.
- Algorithm and Parameters
- FUNC { algorithm-name[S0], data[...] }
The
FUNC subchunk names the procedural and stores its parameters. The name will often
map to a plug-in name. The variable-length data following the name belongs to the
procedural.
Gradient Textures
Texture blocks of type GRAD are gradient textures that modify a surface
channel by mapping an input parameter through an arbitrary transfer function. Gradients
are represented to the user as a line containing keys. Each key is a color, and the
gradient function is an interpolation of the keys in RGB space. The input parameter
selects a point on the line, and the output of the texture is the value of the gradient at
that point.
- Parameter Name
- PNAM { parameter[S0] }
The input
parameter. Possible values include
"Previous Layer"
"Bump"
"Slope"
"Incidence Angle"
"Light Incidence"
"Distance to Camera"
"Distance to Object"
"X Distance to Object"
"Y Distance to Object"
"Z Distance to Object"
"Weight Map"
- Item Name
- INAM { item-name[S0] }
The name of
a scene item. This is used when the input parameter is derived from a property of an item
in the scene.
- Gradient Range
- GRST, GREN { input-range[FP4] }
The
start and end of the input range. These values only affect the display of the gradient in
the user interface. They don't affect rendering.
- Repeat Mode
- GRPT { repeat-mode[U2] }
The repeat
mode. This is currently undefined.
- Key Values
- FKEY { ( input[FP4], output[FP4]
# 4 )* }
The transfer function is defined by an array of keys, each with
an input value and an RGBA output vector. Given an input value, the gradient can be
evaluated by selecting the keys whose positions bracket the value and interpolating
between their outputs. If the input value is lower than the first key or higher than the
last key, the gradient value is the value of the closest key.
- Key Parameters
- IKEY { interpolation[U2] * }
An
array of integers defining the interpolation for the span preceding each key. Possible
values include
0 - Linear
1 - Spline
2 - Step
Shaders
Shaders are BLOK subchunks with a header type of SHDR.
They are applied to a surface after all basic channels and texture layers are evaluated,
and in the order specified by the ordinal sequence. The only header chunk they support is ENAB
and they need only one data chunk to describe them.
- Shader Algorithm
- FUNC { algorithm-name[S0], data[...] }
Just
like a procedural texture layer, a shader is defined by an algorithm name (often a
plug-in), followed by data owned by the shader.
Chunk Index
AAST Image Map Antialiasing Strength
ADTR Surface Additive Transparency
ALPH Surface Alpha Mode
ANIM Clip Animation
AXIS Image Map Major Axis
AXIS Procedural Texture Axis
BBOX Bounding Box
BLOK Surface Block
BRIT Clip Brightness
BUMP Surface Bump Intensity
CHAN Channel Plug-in
CHAN Texture Layer Channel
CLIP Image, Image Sequence
CLRF Surface Color Filter
CLRH Surface Color Highlights
CNTR Texture Center
COLR Surface Base Color
CONT Clip Contrast
CSYS Texture Coordinate System
DESC Description Line
DIFF Surface Diffuse
ENAB Surface Block Enable
ENVL Envelope
FALL Texture Falloff
FKEY Gradient Key Values
FORM IFF Format File
FUNC Procedural Texture Algorithm
FUNC Surface Shader Algorithm
GAMM Clip Gamma Correction
GLOS Surface Specular Glossiness
GLOW Surface Glow Effect
GREN Gradient End
GRPT Gradient Repeat Mode
GRST Gradient Start
HUE Clip Hue
ICON Thumbnail Icon Image
IFLT Clip Image Filter
IKEY Gradient Key Parameters
IMAG Image Map Image
INAM Gradient Item Name
ISEQ Clip Image Sequence
KEY Keyframe Time and Value
LAYR Layer
LINE Surface Render Outlines
LUMI Surface Luminosity
NAME Envelope Channel Name
NEGA Clip Negative
OPAC Texture Layer Opacity
OREF Texture Reference Object
PFLT Clip Pixel Filter
PIXB Image Map Pixel Blending
PNAM Gradient Parameter Name
PNTS Point List
POLS Polygon List
POST Envelope Post-Behavior
PRE Envelope Pre-Behavior
PROJ Image Map Projection Mode
PTAG Polygon Tag Mapping
REFL Surface Reflectivity
RFOP Surface Reflection Options
RIMG Surface Reflection Map Image
RIND Surface Refractive Index
ROTA Texture Rotation
RSAN Surface Reflection Map Image Seam Angle
SPAN Envelope Interval Interpolation
SATR Clip Saturation
SHRP Surface Diffuse Sharpness
SIDE Surface Polygon Sidedness
SIZE Texture Size
SMAN Surface Max Smoothing Angle
SPEC Surface Specularity
STCC Clip Color-cycling Still
STCK
STIL Clip Still Image
SURF Surface Definition
TAGS Tag Strings
TAMP Image Map Texture Amplitude
TEXT Commentary Text
TIME Clip Time
TIMG Surface Refraction Map Image
TMAP Texture Mapping
TRAN Surface Transparency
TRNL Surface Translucency
TROP Surface Transparency Options
TYPE Envelope Type
VALU Procedural Texture Value
VMAD Discontinuous Vertex Map
VMAP Vertex Map
VMAP Image Map UV Vertex Map
WRAP Image Map Wrap Options
WRPW Image Map Width Wrap Amount
WRPH Image Map Height Wrap Amount
XREF Clip Reference (Clone)
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