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./" ./" DO NOT EDIT THIS FILE DIRECTLY! It is generated automatically ./" from the Geomview manual. Make changes in the manual, not here. ./" .TH OOGL 5 "Mon Nov 15 21:35:41 CST 1993" "Geometry Center" .SH NAME OOGL \- File formats for OOGL geometric objects .SH NOTE The material in this manual page also appears in the Geomview manual. .SH DESCRIPTION .nf .na OOGL File Formats ***************** 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. Conventions =========== Syntax Common to All OOGL File Formats -------------------------------------- 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; *Note 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. File Names ---------- 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. Vertices -------- 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 `X Y Z' (3-D floating-point vertex coordinates) or `X Y Z W' (4-D floating-point vertex coordinates) optionally followed by `NX NY NZ' (normalized 3-D surface-normal if present) optionally followed by `R G B A' (4-component floating-point color if present, each component in range 0..1. The A (alpha) component represents opacity: 0 transparent, 1 opaque.) Values are separated by white space, and line breaks are immaterial. Surface normal directions ------------------------- 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. Transformation matrices ----------------------- 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. Binary format ------------- 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' and `OFF' file formats. Details are given in the individual file format descriptions. *Note QUAD::, and *Note OFF::. 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. Embedded objects and external-object references ----------------------------------------------- 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 2 is 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. Appearances ----------- 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", selects "override" status for that attribute. appearance { +face # draw faces of polygons -edge # don't draw edges of polygons -transparent # don't attempt transparency (not implemented) +normal # do draw surface-normal vectors normscale .25 # ... with length .25 in object coordinates +evert # do evert polygon normals where needed so as # to always face the camera shading smooth # or "shading constant" or "shading flat". # smooth = Gouraud shading; flat = faceted. linewidth 3 # lines & edges are 3 pixels wide. 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. alpha 1.0 # opacity; 0 = transparent (invisible) # when transparency is enabled. 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 # are added to those already in the scene. # Now a collection of real 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 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 } # 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. So setting an appearance attribute in an object's definition will prevent the viewer controls from affecting that object's display. Object File Formats =================== `QUAD': collection of quadrilaterals ------------------------------------ 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; *Note 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. `MESH': rectangularly-connected mesh ------------------------------------ The conventional suffix for a `MESH' file is `.mesh'. The file syntax is [C][N][Z][4][U][u][v]MESH # Key word NU NV # Mesh 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 `[C][N][Z][4][U][u][v]MESH'. The optional prefix characters mean: `C' Each vertex (see Vertices above) includes a 4-component color. `N' Each vertex includes a surface normal vector. `Z' Of the 3 vertex position values, only the Z component is present; X and Y are omitted, and assumed to equal the mesh (u,v) coordinate so X ranges from 0 .. (Nu-1), Y from 0 .. (Nv-1) where Nu and Nv are the mesh dimensions -- see below. `4' Vertices are 4D, each consists of 4 floating values. `Z' and `4' cannot both be present. `U' Each vertex includes a 3-component texture space parameter. This is not yet implemented and should not be used. `u' The mesh is wrapped in the u-direction, so the (0,v)'th vertex is connected to the (NU-1,v)'th for all v. `v' The mesh is wrapped in the v-direction, so the (u,0)'th vertex is connected to the (u,NV-1)'th for all u. Thus a u-wrapped or v-wrapped mesh is topologically a cylinder, while a uv-wrapped mesh is a torus. 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; *Note Binary format::. The values of NU and NV are 32-bit integers; all other values are 32-bit floats. Bezier Surfaces --------------- 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 header `S'(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 header `RGBA'(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. OFF Files --------- The conventional suffix for `OFF' files is `.off'. Syntax: [C][N][4]OFF # Header keyword (optional) NVERTICES NFACES NEDGES # NEdges not used or checked X[0] Y[0] Z[0] # Vertices, possibly with colors # and/or normals if `COFF' or `NOFF' ... 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: nothing the default color one integer index into "the" colormap; see below three or four integers RGB and possibly alpha values in the range 0..255 three or four floating-point numbers RGB and possibly alpha values in the range 0..1 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 `[C][N]OFF BINARY' format is accepted; *Note 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 vertex colors or normals if `COFF'/`NOFF'/`CNOFF' 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 VECT Files ---------- 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: 0 No color is specified for this polyline. It's drawn in the same color as the previous polyline. 1 A single color is specified. The entire polyline is drawn in that color. abs(NV[I]) Each vertex has a color. Either each segment is drawn in the corresponding color, or the colors are smoothly interpolated along the line segments, depending on the implementation. 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; *Note 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. INST Files ---------- The conventional suffix for a `INST' file is `.inst'. 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-OBJECT specifies the OOGL object to be instantiated. *Note 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-matrix or ":" symbol-representing-"transform"-object> Another way to specify the transformation is transforms OOGL-OBJECT The 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). This might be useful, e.g., for wrapping an appearance around an externally-supplied object. *Note Transformation matrices::, for the matrix format. There is no INST BINARY format. INST Examples ............. 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 ... } } LIST Files ---------- 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 } } TLIST Files ----------- 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. GROUP Files ----------- 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 } DISCGRP Files ------------- 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). Non-geometric objects ===================== The syntax of these objects is given in the form used in *Note References::, where "quoted" items should appear literally but without quotes, square bracketed ([ ]) items are optional, and | separates alternative choices. Transform Objects ----------------- 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 } } cameras ------- A camera object specifies the following properties of a camera: position and orientation specified by either a camera-to-world or world-to-camera transformation; this transformation does not include the projection, so it's typically just a combination of translation and rotation. Specified as a transform object, typically a 4x4 matrix. "focus" distance Intended to suggest a typical distance from the camera to the object of interest; used for default camera positioning (the camera is placed at (X,Y,Z) = (0,0,focus) when reset) and for adjusting field-of-view when switching between perspective and orthographic views. window aspect ratio True aspect ratio in the sense <Xsize>/<Ysize>. This normally should agree with the aspect ratio of the camera's window. Geomview normally adjusts the aspect ratio of its cameras to match their associated windows. near and far clipping plane distances Note that both must be strictly greater than zero. Very large <far>/<near> distance ratios cause Z-buffering to behave badly; part of an object may be visible even if somewhat more distant than another. field of view Specified in either of two forms. `fov ' is the field of view -- in degrees if perspective, or linear distance if orthographic -- in the *shorter* direction. `halfyfield ' is half the projected Y-axis field, in world coordinates (not angle!), at unit distance from the camera. For a perspective camera, halfyfield is related to angular field: 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) Info file: geomview, -*-Text-*- produced by texinfo-format-buffer from file: geomview.tex window ------ 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.