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The objects that you can load into Geomview are called OOGL objects. OOGL stands for "Object Oriented Graphics Library"; it is the library upon which Geomview is built.
There are many different kinds of OOGL objects. This chapter gives syntactic descriptions of file formats for OOGL objects.
Examples of most file types live in Geomview's `data/geom' directory.
Most OOGL object file formats are free-format ASCII -- any amount of white space (blanks, tabs, newlines) may appear between tokens (numbers, key words, etc.). Line breaks are almost always insignificant, with a couple of exceptions as noted. Comments begin with # and continue to the end of the line; they're allowed anywhere a newline is.
Binary formats are also defined for several objects; See section Binary format, and the individual object descriptions.
Typical OOGL objects begin with a key word designating object type, possibly with modifiers indicating presence of color information etc. In some formats the key word is optional, for compatibility with file formats defined elsewhere. Object type is then determined by guessing from the file suffix (if any) or from the data itself.
Key words are case sensitive. Some have optional prefix letters
indicating presence of color or other data; in this case the order of
prefixes is significant, e.g. CNMESH
is meaningful but
NCMESH
is invalid.
When OOGL objects are read from disk files, the OOGL library uses the file suffix to guess at the file type.
If the suffix is unrecognized, or if no suffix is available (e.g. for an object being read from a pipe, or embedded in another OOGL object), all known types of objects are tried in turn until one accepts the data as valid.
Several objects share a common style of representing vertices with optional per-vertex surface-normal and color. All vertices within an object have the same format, specified by the header key word.
All data for a vertex is grouped together (as opposed to e.g. giving coordinates for all vertices, then colors for all vertices, and so on).
The syntax is
optionally followed by
optionally followed by
optionally followed by
(two or three texture-coordinate values).
Values are separated by white space, and line breaks are immaterial.
Letters in the object's header key word must appear in a specific order; that's the reverse of the order in which the data is given for each vertex. So a `CN4OFF' object's vertices contain first the 4-component space position, then the 3-component normal, finally the 4-component color. You can't change the data order by changing the header key word; an `NCOFF' is just not recognized.
Geomview uses normal vectors to determine how an object is shaded. The direction of the normal is significant in this calculation.
When normals are supplied with an object, the direction of the normal is determined by the data given.
When normals are not supplied with the object, Geomview computes normal vectors automatically; in this case normals point toward the side from which the vertices appear in counterclockwise order.
On parametric surfaces (Bezier patches), the normal at point P(u,v) is in the direction dP/du cross dP/dv.
Some objects incorporate 4x4 real matrices for homogeneous object transformations. These matrices act by multiplication on the right of vectors. Thus, if p is a 4-element row vector representing homogeneous coordinates of a point in the OOGL object, and A is the 4x4 matrix, then the transformed point is p' = p A. This matrix convention is common in computer graphics; it's the transpose of that often used in mathematics, where points are column vectors multiplied on the right of matrices.
Thus for Euclidean transformations, the translation components appear in the fourth row (last four elements) of A. A's last column (4th, 8th, 12th and 16th elements) are typically 0, 0, 0, and 1 respectively.
Many OOGL objects accept binary as well as ASCII file formats.
These files begin with the usual ASCII token (e.g. CQUAD
)
followed by the word BINARY
.
Binary data begins at the byte following the first newline after
BINARY
. White space and a single comment may intervene, e.g.
OFF BINARY # binary-format "OFF" data follows
Binary data comprise 32-bit integers and 32-bit IEEE-format floats, both in big-endian format (i.e., with most significant byte first). This is the native format for 'int's and 'float's on Sun-3's, Sun-4's, and Irises, among others.
Binary data formats resemble the corresponding ASCII formats, with ints
and floats in just the places you'd expect. There are some exceptions
though, specifically in the QUAD
, OFF
and COMMENT
file formats. Details are given in the individual file format
descriptions. See section QUAD: collection of quadrilaterals, See section OFF Files, and See section COMMENT Objects.
Binary OOGL objects may be freely mixed in ASCII object streams:
LIST { = MESH BINARY ... binary data for mesh here ... } { = QUAD 1 0 0 0 0 1 0 1 0 0 1 0 }
Note that ASCII data resumes immediately following the last byte of binary data.
Naturally, it's impossible to embed comments inside a binary-format OOGL object, though comments may appear in the header before the beginning of binary data.
Some object types (LIST
, INST
) allow references to other
OOGL objects, which may appear literally in the data stream, be loaded
from named disk files, or be communicated from elsewhere via named
objects. Gcl commands also accept geometry in these forms.
The general syntax is
<oogl-object> ::= [ "{" ] [ "define"symbolname
] [ "appearance"appearance
] [ ["="]object-keyword
... | "<"filename
| ":"symbolname
] [ "}" ]
where "quoted" items are literal strings (which appear without the quotes), [bracketed] items are optional, and | denotes alternatives. Curly braces, when present, must match; the outermost set of curly braces is generally required when the object is in a larger context, e.g. when it is part of a larger object or embedded in a Geomview command stream.
For example, each of the following three lines:
{ define fred QUAD 1 0 0 0 0 1 0 1 0 1 0 0 } { appearance { +edge } LIST { < "file1" } { : fred } } VECT 1 2 0 2 0 0 0 0 1 1 2is a valid OOGL object. The last example is only valid when it is delimited unambiguously by residing in its own disk file.
The "<" construct causes a disk file to be read. Note that this isn't a general textual "include" mechanism; a complete OOGL object must appear in the referenced file.
Files read using "<" are sought first in the directory of the file which
referred to them, if any; failing that, the normal search path (set by
Geomview's load-path
command) is used. The default search looks
first in the current directory, then in the Geomview data directories.
The ":" construct allows references to symbols, created with
define
. A symbol's initial value is a null object. When a
symbol is (re)defined, all references to it are automatically changed;
this is a crucial part of the support for interprocess communication.
Some future version of the documentation should explain this better...
Again, white space and line breaks are insignificant, and "#" comments may appear anywhere.
Geometric objects can have associated "appearance" information,
specifying shading, lighting, color, wireframe vs. shaded-surface
display, and so on. Appearances are inherited through object
hierarchies, e.g. attaching an appearance to a LIST
means that the
appearance is applied to all the LIST
's members.
Some appearance-related properties are relegated to "material" and "lighting" substructures. Take care to note which properties belong to which structure.
Here's an example appearance structure including values for all attributes. Order of attributes is unimportant. As usual, white space is irrelevant. Boolean attributes may be preceded by "+" or "-" to turn them on or off; "+" is assumed if only the attribute name appears. Other attributes expect values.
A "*" prefix on any attribute, e.g. "*+edge" or "*linewidth 2" or "material { *diffuse 1 1 .25 }", selects "override" status for that attribute.
appearance { +face # (Do) draw faces of polygons. On by default. -edge # (Don't) draw edges of polygons +vect # (Do) draw VECTs. On by default. -transparent # (Disable) transparency. enabling transparency # does NOT result in a correct Geomview picture, # but alpha values are used in RenderMan snapshots. -normal # (Do) draw surface-normal vectors normscale 1 # ... with length 1.0 in object coordinates +evert # do evert polygon normals where needed so as # to always face the camera -texturing # (Disable) texture mapping -backcull # (Don't) discard clockwise-oriented faces -concave # (Don't) expect and handle concave polygons -shadelines # (Don't) shade lines as if they were lighted cylinders # These four are only effective where the graphics system # supports them, namely on GL and Open GL. -keepcolor # Normally, when N-D positional coloring is enabled as # with geomview's (ND-color ...) command, all # objects' colors are affected. But, objects with the # "+keepcolor" attribute are immune to N-D coloring. shading smooth # or "shading constant" or "shading flat" or # or "shading csmooth". # smooth = Gouraud shading, flat = faceted, # csmooth = smoothly interpolated but unlighted. linewidth 1 # lines, points, and edges are 1 pixel wide. patchdice 10 10 # subdivide Bezier patches this finely in u and v material { # Here's a material definition; # it could also be read from a file as in # "material < file.mat" ka 1.0 # ambient reflection coefficient. ambient .3 .5 .3 # ambient color (red, green, blue components) # The ambient contribution to the shading is # the product of ka, the ambient color, # and the color of the ambient light. kd 0.8 # diffuse-reflection coefficient. diffuse .9 1 .4 # diffuse color. # (In "shading constant" mode, the surface # is colored with the diffuse color.) ks 1.0 # specular reflection coefficient. specular 1 1 1 # specular (highlight) color. shininess 25 # specular exponent; larger values give # sharper highlights. backdiffuse .7 .5 0 # back-face color for two-sided surfaces # If defined, this field determines the diffuse # color for the back side of a surface. # It's implemented by the software shader, and # by hardware shading on GL systems which support # two-sided lighting, and under Open GL. alpha 1.0 # opacity; 0 = transparent (invisible), 1 = opaque. # Ignored when transparency is disabled. edgecolor 1 1 0 # line & edge color normalcolor 0 0 0 # color for surface-normal vectors } lighting { # Lighting model ambient .3 .3 .3 # ambient light replacelights # "Use only the following lights to # illuminate the objects under this # appearance." # Without "replacelights", any lights listed # are added to those already in the scene. # Now a collection of sample lights: light { color 1 .7 .6 # light color position 1 0 .5 0 # light position [distant light] # given in homogeneous coordinates. # With fourth component = 0, # this means a light coming from # direction (1,0,.5). } light { # Another light. color 1 1 1 position 0 0 .5 1 # light at finite position ... location camera # specified in camera coordinates. # (Since the camera looks toward -Z, # this example places the light # .5 unit behind the eye.) # Possible "location" keywords: # global light position is in world (well, universe) coordinates # This is the default if no location specified. # camera position is in the camera's coordinate system # local position is in the coordinate system where # the appearance was defined } } # end lighting model texture { clamp st # or "s" or "t" or "none" file lump.tiff # file supplying texture-map image alphafile mask.pgm.Z # file supplying transparency-mask image apply blend # or "modulate" or "decal" transform 1 0 0 0 # surface (s,t,0,1) * tfm -> texture coords 0 1 0 0 0 0 1 0 .5 0 0 1 background 1 0 0 1 # relevant for "apply blend" } } # end appearance
There are rules for inheritance of appearance attributes when several are imposed at different levels in the hierarchy.
For example, Geomview installs a backstop appearance which provides default values for most parameters; its control panels install other appearances which supply new values for a few attributes; user-supplied geometry may also contain appearances.
The general rule is that the child's appearance (the one closest to the geometric primitives) wins. Further, appearance controls with "override" status (e.g. *+face or material { *diffuse 1 1 0 }) win over those without it.
Geomview's appearance controls use the "override" feature so as to be effective even if user-supplied objects contain their own appearance settings. However, if a user-supplied object contains an appearance field with override status set, that property will be immune to Geomview's controls.
Some platforms support texture-mapped objects.
(On those which don't, attempts to use texture mapping are silently
ignored.) A texture is specified as part of an appearance structure,
as in See section Appearances. Briefly, one provides a texture image,
which is considered to lie in a square in (s,t)
parameter space in
the range 0 <= s <= 1, 0 <= t <= 1. Then one provides a geometric primitive,
with each vertex tagged with (s,t)
texture coordinates. If texturing
is enabled, the appropriate portion of the texture image is pasted onto
each face of the textured object.
There is (currently) no provision for inheritance of part of a texture
structure; if the texture
keyword is mentioned in an appearance,
it supplants any other texture specification.
The appearance attribute texturing
controls whether textures are
used; there's no performance penalty for having texture { ... } fields
defined when texturing is off.
The available fields are:
clamp none -or- s -or- t -or- st Determines the meaning of texture coordinates outside the range 0..1. Withclamp none
, the default, coordinates are interpreted modulo 1, so (s,t) = (1.25,0), (.25,0), and (-.75,0) all refer to the same point in texture space. Withs
ort
orst
, either or both of s- or t-coordinates less than 0 or greater than 1 are clamped to 1 or 0, respectively. file filename alphafile filename Specifies image file(s) containing the texture. Thefile
file's image specifies color or lightness information; thealphafile
if present, specifies a transparency ("alpha") mask; where the mask is zero, pixels are simply not drawn. Several image file formats are available; the file type must be indicated by the last few characters of the file name: .ppm or .ppm.Z or .ppm.gz 24-bit 3-color image in PPM format .pgm or .pgm.Z or .pgm.gz 8-bit grayscale image in PGM format .sgi or .sgi.Z or .sgi.gz 8-bit, 24-bit, or 32-bit SGI image .tiff 8-bit or 24-bit TIFF image .gif GIF image (Though 4-channel TIFF images are possible, and could represent both color and transparency information in one image, that's not supported in geomview at present.) For this feature to work, some programs must be available in geomview's search path: zcat for .Z files gzip for .gz files tifftopnm for .tiff files giftoppm for .gif files If analphafile
image is supplied, it must be the same size as thefile
image. apply modulate -or- blend -or- decal Indicates how the texture image is applied to the surface. Here the "surface color" means the color that surface would have in the absence of texture mapping. Withmodulate
, the default, the texture color (or lightness, if textured by a gray-scale image) is multiplied by the surface color. Withblend
, texture blends between thebackground
color and the surface color. Thefile
parameter must specify a gray-scale image. Where the texture image is 0, the surface color is unaffected; where it's 1, the surface is painted in the color given bybackground
; and color is interpolated for intermediate values. Withdecal
, thefile
parameter must specify a 3-color image. If analphafile
parameter is present, its value interpolates between the surface color (where alpha=0) and the texture color (where alpha=1). Lighting does not affect the texture color indecal
mode; effectively the texture is constant-shaded. background R G B A Specifies a 4-component color, with R, G, B, and A floating-point numbers normally in the range 0..1, used whenapply blend
is selected. transformtransformation-matrix
Expects a list of 16 numbers, or one of the other ways of representing a transformation (: handlename
or< filename
). The 4x4 transformation matrix is applied to texture coordinates, in the sense of a 4-component row vector (s,t,0,1) multiplied on the left of the matrix, to produce new coordinates (s',t') which actually index the texture.
The conventional suffix for a QUAD
file is `.quad'.
The file syntax is
[C][N][4]QUAD -or- [C][N][4]POLY # Key word vertex vertex vertex vertex # 4*N vertices for some N vertex vertex vertex vertex ...
The leading key word is [C][N][4]QUAD
or [C][N][4]POLY
,
where the optional C
and N
prefixes indicate that each vertex
includes colors and normals respectively. That is, these files
begin with one of the words
QUAD
CQUAD
NQUAD
CNQUAD
POLY
CPOLY
NPOLY
CNPOLY
(but not NCQUAD
or NCPOLY
). QUAD
and POLY
are synonymous; both forms are allowed just for compatibility with
ChapReyes.
Following the key word is an arbitrary number of groups of four vertices, each group describing a quadrilateral. See the Vertex syntax above. The object ends at end-of-file, or with a closebrace if incorporated into an object reference (see above).
A QUAD BINARY
file format is accepted; See section Binary format. The
first word of binary data must be a 32-bit integer giving the number of
quads in the object; following that is a series of 32-bit floats,
arranged just as in the ASCII format.
The conventional suffix for a MESH
file is `.mesh'.
The file syntax is
[U][C][N][Z][4][u][v][n]MESH # Key word [Ndim] # Space dimension, present only if nMESH Nu Nv # Mesh grid dimensions # Nu*Nv vertices, in format specified # by initial key word vertex(u=0,v=0) vertex(1,0) ... vertex(Nu-1,0) vertex(0,1) ... vertex(Nu-1,1) ... vertex(0,Nv-1) ... vertex(Nu-1,Nv-1)
The key word is [U][C][N][Z][4][u][v][n]MESH
.
The optional prefix characters mean:
S
and T
texture
parameters for that vertex; the third should be specified as zero.
Z
and
4
cannot both be present.
Note that the order of prefix characters is significant; a colored,
u-wrapped mesh is a CuMESH
not a uCMESH
.
Following the mesh header are integers Nu and Nv, the dimensions of the mesh.
Then follow Nu*Nv vertices, each in the form given by the header. They appear in v-major order, i.e. if we name each vertex by (u,v) then the vertices appear in the order
(0,0) (1,0) (2,0) (3,0) ... (Nu-1,0) (0,1) (1,1) (2,1) (3,1) ... (Nu-1,1) ... (0,Nv-1) ... (Nu-1,Nv-1)
A MESH BINARY
format is accepted; See section Binary format. The
values of Nu and Nv are 32-bit integers; all other values
are 32-bit floats.
The conventional file suffixes for Bezier surface files are `.bbp' or `.bez'. A file with either suffix may contain either type of patch.
Syntax:
[ST]BBP -or- [C]BEZ<Nu><Nv><Nd>[_ST] # Nu, Nv are u- and v-direction # polynomial degrees in range 1..6 # Nd = dimension: 3->3-D, 4->4-D (rational) # (The '<' and '>' do not appear in the input.) # Nu,Nv,Nd are each a single decimal digit. # BBP form implies Nu=Nv=Nd=3 so BBP = BEZ333. # Any number of patches follow the header # (Nu+1)*(Nv+1) patch control points # each 3 or 4 floats according to header vertex(u=0,v=0) vertex(1,0) ... vertex(Nu,0) vertex(0,1) ... vertex(Nu,1) ... vertex(0,Nv) ... vertex(Nu,Nv) # ST texture coordinates if mentioned in headerS
(u=0,v=0)T
(0,0)S
(0,Nv)T
(0,Nv)S
(Nu,0)T
(Nu,0)S
(Nu,Nv)T
(Nu,Nv) # 4-component float (0..1) R G B A colors # for each patch corner if mentioned in headerRGBA
(0,0)RGBA
(0,Nv)RGBA
(Nu,0)RGBA
(Nu,Nv)
These formats represent collections of Bezier surface patches, of degrees up to 6, and with 3-D or 4-D (rational) vertices.
The header keyword has the forms [ST]BBP
or
[C]BEZ<Nu><Nv><Nd>[_ST]
(the '<' and '>' are
not part of the keyword.
The ST
prefix on BBP
, or _ST
suffix on
BEZuvn
, indicates that each patch includes four pairs of
floating-point texture-space coordinates, one for each corner of the
patch.
The C
prefix on BEZuvn
indicates a colored patch,
including four sets of four-component floating-point colors (red, green,
blue, and alpha) in the range 0..1, one color for each corner.
Nu and Nv, each a single digit in the range 1..6, are the patch's polynomial degree in the u and v direction respectively.
Nd is the number of components in each patch vertex, and must be
either 3
for 3-D or 4
for homogeneous coordinates, that
is, rational patches.
BBP
patches are bicubic patches with 3-D vertices, so BBP
= BEZ333
and STBBP
= BEZ333_ST
.
Any number of patches follow the header. Each patch comprises a series of patch vertices, followed by optional (s,t) texture coordinates, followed by optional (r,g,b,a) colors.
Each patch has (Nu+1)*(Nv+1) vertices in v-major order, so that if we designate a vertex by its control point indices (u,v) the order is
(0,0) (1,0) (2,0) ... (Nu,0) (0,1) (1,1) (2,1) ... (Nu,1) ... (0,Nv) ... (Nu,Nv)with each vertex containing either 3 or 4 floating-point numbers as specified by the header. If the header calls for ST coordinates, four pairs of floating-point numbers follow: the texture-space coordinates for the (0,0), (Nu,0), (0,Nv), and (Nu,Nv) corners of the patch, respectively.
If the header calls for colors, four four-component (red, green, blue, alpha) floating-point colors follow, one for each patch corner.
The series of patches ends at end-of-file, or with a closebrace if incorporated in an object reference.
The conventional suffix for OFF
files is `.off'.
Syntax:
[ST][C][N][4][n]OFF # Header keyword [Ndim] # Space dimension of vertices, present only if nOFF NVertices NFaces NEdges # NEdges not used or checked x[0] y[0] z[0] # Vertices, possibly with normals, # colors, and/or texture coordinates, in that order, # if the prefixesN
,C
,ST
# are present. # If 4OFF, each vertex has 4 components, # including a final homogeneous component. # If nOFF, each vertex has Ndim components. # If 4nOFF, each vertex has Ndim+1 components. ... x[NVertices-1] y[NVertices-1] z[NVertices-1] # Faces # Nv = # vertices on this face # v[0] ... v[Nv-1]: vertex indices # in range 0..NVertices-1 Nv v[0] v[1] ... v[Nv-1] colorspec ... # colorspec continues past v[Nv-1] # to end-of-line; may be 0 to 4 numbers # nothing: default # integer: colormap index # 3 or 4 integers: RGB[A] values 0..255 # 3 or 4 floats: RGB[A] values 0..1
OFF
files (name for "object file format") represent collections
of planar polygons with possibly shared vertices, a convenient way to
describe polyhedra. The polygons may be concave but there's no
provision for polygons containing holes.
An OFF
file may begin with the keyword OFF
; it's
recommended but optional, as many existing files lack this keyword.
Three ASCII integers follow: NVertices, NFaces, and NEdges. Thse are the number of vertices, faces, and edges, respectively. Current software does not use nor check NEdges; it needn't be correct but must be present.
The vertex coordinates follow: dimension * Nvertices
floating-point values. They're implicitly numbered 0 through
NVertices-1. dimension is either 3 (default) or 4 (specified by
the key character 4
directly before OFF
in the keyword).
Following these are the face descriptions, typically written with one line per face. Each has the form
N Vert1 Vert2 ... VertN [color]Here N is the number of vertices on this face, and Vert1 through VertN are indices into the list of vertices (in the range 0..NVertices-1).
The optional color may take several forms. Line breaks are significant here: the color description begins after VertN and ends with the end of the line (or the next # comment). A color may be:
For the one-integer case, the colormap is currently read from the file `cmap.fmap' in Geomview's `data' directory. Some better mechanism for supplying a colormap is likely someday.
The meaning of "default color" varies. If no face of the object has a color, all inherit the environment's default material color. If some but not all faces have colors, the default is gray (R,G,B,A=.666).
A [ST][C][N][n]OFF BINARY
format is accepted; See section Binary format. It
resembles the ASCII format in almost the way you'd expect, with 32-bit
integers for all counters and vertex indices and 32-bit floats for
vertex positions (and texture coordinates or vertex colors or normals if
COFF
/NOFF
/CNOFF
/STCNOFF
/etc. format).
Exception: each face's vertex indices are followed by an integer indicating how many color components accompany it. Face color components must be floats, not integer values. Thus a colorless triangular face might be represented as
int int int int int 3 17 5 9 0
while the same face colored red might be
int int int int int float float float float 3 17 5 9 4 1.0 0.0 0.0 1.0
The conventional suffix for VECT
files is `.vect'.
Syntax:
[4]VECT NPolylines NVertices NColors Nv[0] ... Nv[NPolylines-1] # number of vertices # in each polyline Nc[0] ... Nc[NPolylines-1] # number of colors supplied # in each polyline Vert[0] ... Vert[NVertices-1] # All the vertices # (3*NVertices floats) Color[0] ... Color[NColors-1] # All the colors # (4*NColors floats, RGBA)
VECT
objects represent lists of polylines (strings of connected
line segments, possibly closed). A degenerate polyline can be used to
represent a point.
A VECT
file begins with the key word VECT
or 4VECT
and three integers: NLines, NVertices, and NColors.
Here NLines is the number of polylines in the file,
NVertices the total number of vertices, and NColors the
number of colors as explained below.
Next come NLines integers
Nv[0] Nv[1] Nv[2] ... Nv[NLines-1]
giving the number of vertices in each polyline. A negative number indicates a closed polyline; 1 denotes a single-pixel point. The sum (of absolute values) of the Nv[i] must equal NVertices.
Next come NLines more integers Nc[i]: the number of colors in each polyline. Normally one of three values:
The sum of the Nc[i] must equal NColors.
Next come NVertices groups of 3 or 4 floating-point numbers: the coordinates of all the vertices. If the keyword is 4VECT then there are 4 values per vertex. The first abs(Nv[0]) of them form the first polyline, the next abs(Nv[1]) form the second and so on.
Finally NColors groups of 4 floating-point numbers give red, green, blue and alpha (opacity) values. The first Nc[0] of them apply to the first polyline, and so on.
A VECT BINARY format is accepted; See section Binary format. The binary format exactly follows the ASCII format, with 32-bit ints where integers appear, and 32-bit floats where real values appear.
SKEL
files represent collections of points and polylines, with
shared vertices.
The conventional suffix for SKEL
files is `.skel'.
Syntax:
[4][n]SKEL [NDim] # Vertex dimension, present only if nSKEL NVertices NPolylines x[0] y[0] z[0] # Vertices # (if nSKEL, each vertex has NDim components) ... x[NVertices-1] y[NVertices-1] z[NVertices-1] # Polylines # Nv = # vertices on this polyline (1 = point) # v[0] ... v[Nv-1]: vertex indices # in range 0..NVertices-1 Nv v[0] v[1] ... v[Nv-1] [colorspec] ... # colorspec continues past v[Nv-1] # to end-of-line; may be nothing, or 3 or 4 numbers. # nothing: default color # 3 or 4 floats: RGB[A] values 0..1
The syntax resembles that of OFF
files, with a table of vertices
followed by a sequence of polyline descriptions, each referring to vertices
by index in the table. Each polyline has an optional color.
For nSKEL
objects, each vertex has NDim components.
For 4nSKEL
objects, each vertex has NDim+1 components;
the final component is the homogeneous divisor.
No BINARY
format is implemented as yet for SKEL
objects.
The conventional suffix for SPHERE
files is `.sph'.
SPHERE Radius Xcenter Ycenter Zcenter
Sphere objects are drawn using rational Bezier patches, which are diced into
meshes; their smoothness, and the time taken to draw them, depends on the
setting of the dicing level, 10x10 by default.
From Geomview, the Appearance panel, the <N>ad
keyboard command, or
a dice nu nv
Appearance attribute sets this.
The conventional suffix for a INST
file is `.inst'.
There is no INST BINARY format.
An INST
applies a 4x4 transformation to another OOGL object. It
begins with INST
followed by these sections which may appear in
any order:
geom oogl-objectspecifies the OOGL object to be instantiated. See section Embedded objects and external-object references, for the syntax of an oogl-object. The keyword
unit
is a
synonym for geom
.
transform ["{"] 4x4 transform
["}"]
specifies a single transformation matrix. Either the
matrix may appear literally as 16 numbers, or there may be
a reference to a "transform" object, i.e.
"<" file-containing-4x4-matrixor
":" symbol-representing-transform-object>Another way to specify the transformation is
transforms oogl-objectThe oogl-object must be a
TLIST
object (list of
transformations) object, or a LIST
whose members are ultimately
TLIST
objects. In effect, the transforms
keyword takes a
collection of 4x4 matrices and replicates the geom
object, making
one copy for each 4x4 matrix.
If no transform
nor transforms
keyword appears, no
transformation is applied (actually the identity is applied). You could
use this for, e.g., wrapping an appearance around an externally-supplied
object, though a single-membered LIST would do this more efficiently.
See section Transformation matrices, for the matrix format.
Two more INST fields are accepted: location
and origin
.
location [global or camera or ndc or screen or local]Normally an INST specifies a position relative to its parent object; the
location
field allows putting an object elsewhere.
location global
attaches the object to the global (a.k.a. universe)
coordinate system -- the same as that in which geomview's World objects,
alien geometry, and cameras are placed.
location camera
places the object relative to the camera.
(Thus if there are multiple views, it may appear in a different
spatial position in each view.) The center of the camera's view
is along its negative Z axis; positive X is rightward, positive Y upward.
Normally the units of camera space are the same as global coordinates.
When a camera is reset, the global origin is at (0,0,-3.0).
location ndc
places the object relative to the normalized unit
cube into which the camera's projection (perspective or orthographic)
maps the visible world. X, Y, and Z are each in the range from -1 to +1,
with Z = -1 the near and Z = +1 the far clipping plane, and X and Y
increasing rightward and upward respectively.
Thus something like
INST transform 1 0 0 0 0 1 0 0 0 0 1 0 -.9 -.9 -.999 1 location ndc geom < label.vectpastes
label.vect
onto the lower left corner of each window,
and in front of nearly everything else, assuming label.vect
's
contents lie in the positive quadrant of the X-Y plane.
It's tempting to use -1 rather than -.999 as the Z component of the
position, but that may put the object just nearer than the near clipping
plane and make it (partially) invisible, due to floating-point error.
location screen
places the object in screen coordinates.
The range of Z is still -1 through +1 as for ndc coordinates;
X and Y are measured in pixels, and range from (0,0) at the lower left
corner of the window, increasing rightward and upward.
location local
is the default; the object is positioned relative
to its parent.
origin [global or camera or ndc or screen or local] x y zThe
origin
field translates the contents of the INST to
place the origin at the specified point of the given coordinate system.
Unlike location
, it doesn't change the orientation, only the choice
of origin. Both location
and origin
can be used together.
So for example
{ INST location screen origin ndc 0 0 -.99 geom { < xyz.vect } transform { 100 0 0 0 0 100 0 0 0 0 -.009 0 0 0 0 1 } }
places xyz.vect's origin in the center of the window, just beyond the near clipping plane. The unit-length X and Y edges are scaled to be just 100 screen units -- pixels -- long, regardless of the size of the window.
Here are some examples of INST
files
INST unit < xyz.vect transform { 1 0 0 0 0 1 0 0 0 0 1 0 1 3 0 1 }
{ appearance { +edge material { edgecolor 1 1 0 } } INST geom < mysurface.quad }
{INST transform {: T} geom {<dodec.off}}
{ INST transforms { LIST { < some-matrices.prj } { < others.prj } { TLIST <still more of them> } } geom { # stuff replicated by all the above matrices ... } }
This one resembles the origin
example in the section above,
but makes the X and Y edges be 1/4 the size of the window (1/4, not 1/2,
since the range of ndc X and Y coordinates is -1 to +1).
{ INST location ndc geom { < xyz.vect } transform { .5 0 0 0 0 .5 0 0 0 0 -.009 0 0 0 -.99 1 } }
The conventional suffix for a LIST
file is `.list'.
A list of OOGL objects
Syntax:
LIST oogl-object oogl-object ...
Note that there's no explicit separation between the oogl-objects, so they should be enclosed in curly braces ({ }) for sanity. Likewise there's no explicit marker for the end of the list; unless appearing alone in a disk file, the whole construct should also be wrapped in braces, as in:
{ LIST { QUAD ... } { < xyz.quad } }
A LIST
with no elements, i.e. { LIST }
, is valid, and is
the easiest way to create an empty object. For example, to remove a
symbol's definition you might write
{ define somesymbol { LIST } }
The conventional suffix for a TLIST
file is `.grp' ("group")
or or `.prj' ("projective" matrices).
Collection of 4x4 matrices, used in the transforms
section of and
INST
object.
Syntax:
TLIST # key word <4x4 matrix (16 floats)> ... # Any number of 4x4 matrices
TLIST
s are used only within the transforms
clause of an
INST
object. They cause the INST
s geom
object to
be instantiated once under each of the transforms in the TLIST
.
The effect is like that of a LIST
of INST
s each with a
single transform, and all referring to the same object, but is more
efficient.
Be aware that a TLIST
is a kind of geometry object, distinct from a
transform
object. Some contexts expect one type of object,
some the other. For example in
INST transform { : myT } geom { ... }myT must be a transform object, which might have been created with the gcl
(read transform { define myT 1 0 0 1 ... })while in
INST transforms { : myTs } geom { ... } or INST transforms { LIST {: myTs} {< more.prj} } geom { ... }myTs must be a geometry object, defined e.g. with
(read geometry { define myTs { TLIST 1 0 0 1 ... } })
A TLIST BINARY
format is accepted. Binary data begins with a
32-bit integer giving the number of transformations, followed by that
number of 4x4 matrices in 32-bit floating-point format. The order of
matrix elements is the same as in the ASCII format.
This format is obsolete, but is still accepted. It combined the
functions of INST
and TLIST
, taking a series of
transformations and a single Geom (unit
) object, and replicating
the object under each transformation.
GROUP ... < matrices > ... unit { oogl-object }
is still accepted and effectively translated into
INST transforms { TLIST ... <matrices> ... } unit { oogl-object }
This format is for discrete groups, such as appear in the theory of manifolds or in symmetry patterns. This format has its own man page. See discgrp(5).
The COMMENT object is a mechanism for encoding arbitrary data within an OOGL object. It can be used to keep track of data or pass data back and forth between external modules.
Syntax:
COMMENT # key word name type # individual name and type specifier { ... } # arbitrary data
The data, which must be enclosed by curly braces, can include anything except unbalanced curly braces. The type field can be used to identify data of interest to a particular program through naming conventions.
COMMENT
objects are intended to be associated with other objects
through inclusion in a LIST
object. (See section LIST Files.) The "#" OOGL
comment syntax does not suffice for data exchange since these comments
are stripped when an OOGL object is read in to Geomview. The
COMMENT
object is preserved when loaded into Geomview and is
written out intact.
Here is an example associating a WorldWide Web URL with a piece of geometry:
{ LIST { < Tetrahedron} {COMMENT GCHomepage HREF { http://www.geom.umn.edu/ }} }
A binary COMMENT
format is accepted. Its format is not consistent
with the other OOGL binary formats. See section Binary format. The
name
and type
are followed by
N Byte1 Byte2 ... ByteNinstead of data enclosed in curly braces.
The syntax of these objects is given in the form used in See section Embedded objects and external-object references, where "quoted" items should appear literally but without quotes, square bracketed ([ ]) items are optional, and | separates alternative choices.
Where a single 4x4 matrix is expected -- as in the
INST
transform
field, the camera's camtoworld
transform
and the Geomview xform*
commands -- use a transform object.
Note that a transform is distinct from a TLIST
, which is a type
of geometry. TLIST
s can contain one or more 4x4 transformations;
"transform" objects must have exactly one.
Why have both? In many places -- e.g. camera positioning -- it's only meaningful to have a single transform. Using a separate object type enforces this.
Syntax for a transform object is
<transform> ::= [ "{" ] (curly brace, generally needed to make the end of the object unambiguous.) [ "transform" ] (optional keyword; unnecessary if the type is determined by the context, which it usually is.) [ "define" <name> ] (defines a transform named <name>, setting its value from the stuff which follows) <sixteen floating-point numbers> (interpreted as a 4x4 homogeneous transform given row by row, intended to apply to a row vector multiplied on its LEFT, so that e.g. Euclidean translations appear in the bottom row) | "<" <filename> (meaning: read transform from that file) | ":" <name> (meaning: use variable <name>, defined elsewhere; if undefined the initial value is the identity transform) [ "}" ] (matching curly brace)
The whole should be enclosed in { braces }. Braces are not essential if exactly one of the above items is present, so e.g. a 4x4 array of floats standing alone may but needn't have braces.
Some examples, in contexts where they might be used:
# Example 1: A gcl command to define a transform # called "fred" (read transform { transform define fred 1 0 0 0 0 1 0 0 0 0 1 0 -3 0 1 1 } )
# Example 2: A camera object using transform # "fred" for camera positioning # Given the definition above, this puts the camera at # (-3, 0, 1), looking toward -Z. { camera halfyfield 1 aspect 1.33 camtoworld { : fred } }
A camera object specifies the following properties of a camera:
halfyfield = tan( Y_axis_angular_field / 2 )
while for an orthographic one it's simply:
halfyfield = Y_axis_linear_field / 2
This odd-seeming definition is (a) easy to calculate with and (b) well-defined in both orthographic and perspective views.
The syntax for a camera is:
<camera> ::= [ "camera" ] (optional keyword) [ "{" ] (opening brace, generally required) [ "define" <name> ] "<" <filename> | ":" <name> | (or any number of the following, in any order...) "perspective" {"0" | "1"} (default 1) (otherwise orthographic) "stereo" {"0" | "1"} (default 0) (otherwise mono) "worldtocam" <transform> (see transform syntax above) "camtoworld" <transform> (no point in specifying both camtoworld and worldtocam; one is constrained to be the inverse of the other) "halfyfield" <half-linear-Y-field-at-unit-distance> (default tan 40/2 degrees) "fov" (angular field-of-view if perspective, linear field-of-view otherwise. Measured in whichever direction is smaller, given the aspect ratio. When aspect ratio changes -- e.g. when a window is reshaped -- "fov" is preserved.) "frameaspect" <aspect-ratio> (X/Y) (default 1.333) "near" <near-clipping-distance> (default 0.1) "far" <far-clipping-distance> (default 10.0) "focus" <focus-distance> (default 3.0) [ "}" ] (matching closebrace)
A window object specifies size, position, and other window-system related information about a window in a device-independent way.
The syntax for a window object is:
window ::= [ "window" ] (optional keyword) [ "{" ] (curly brace, often required) (any of the following, in any order) "size" <xsize> <ysize> (size of the window) "position" <xmin> <xmax> <ymin> <ymax> (position & size) "noborder" (specifies the window should have no window border) "pixelaspect" <aspect> (specifies the true visual aspect ratio of a pixel in this window in the sense xsize/ysize, normally 1.0. For stereo hardware which stretches the display vertically by a factor of 2, "pixelaspect 0.5" might do. The value is used when computing the projection of a camera associated with this window.) [ "}" ] (matching closebrace)
Window objects are used in the Geomview window
and
ui-panel
commands to set default properties for future windows or
to change those of an existing window.
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