8
Definitions
ambient light
A light source that enters into the reflectance calculation independently of
the orientation of the area being illuminated of the location of the eye.
ambient reflection coefficient
The fraction of ambient light reflected from an area.
area primitive
Any of the output primitives : fill area, fill area set, cell array, fill area
set with data, cell array PLUS, set of fill area set with data, triangle strip
with data, triangle set with data, quadrilateral mesh with data, non uniform
B-spline surface and non uniform B spline surface with data. In addition, some
generalized drawing primitives may have this classification.
attenuation coefficient
A parameter in an expression that models the decrease in intensity of light as
a function of the distance from a light source to an illuminated object. Such
expressions are typically used to simulate the light attenuating effects of
different media, e.g., fog, water and air.
back face
any facet of an area primitive whose geometric normal when transformed to NPC
has a negative Z component.
bundle table entry
A single entry in a bundle table. Each entry contains one value for each aspect
which applies to the corresponding output primitive. This set is workstation
dependant.
color mapping
The conversion of direct colors in the rendering pipeline to other colors
before they are displayed on the workstation.
cell array
output primitive consisting of a parallelogram of equal sized cells, each of
which is a parallelogram and has a single color.
centralized structure store(CSS)
The conceptual workstation independent storage area for structure networks.
character base vector
An aspect of text which defines the direction of the baseline of a character.
It id a two-dimensional vector in the text plane specified in the "text"
structure element.
character body
The rectangle defining the horizontal and vertical limits of an individual
character.
character expansion factor
An aspect of text which specifies the deviation of character width from the
defined nominal value of a given font on a given workstation.
character height
An aspect of text of which specifies the nominal value for the height of an
upper case character.
character set
A registered interpretation for entries in the character code table (see ISO
2022).
character spacing
An aspect of text which specifies the fraction of the font nominal value for
character height to be added between adjacent character bodies in a string.
character up vector
An aspect of text which defines the principal up direction of the text string.
It is a two-dimensional vector in the plane specified in the "text" structure
element.
character width
An aspect of text which specifies the nominal value of the width of a
character. The actual width depend on the width to height ratio specified by
the designer of the font to which the character belongs.
child structure
A structure specified in a structure reference.
choice device
A logical input device providing a non-negative integer defining one of a set
of alternatives.
CIE
Abbreviation for the Commission Internationale de l'Eclairage. Used to refer to
the CIE universal color definition system used as a color model.
CIELUV
Abbreviation for the CIE 1976 ("LUV") color space.
clipping
Removing parts of output primitives which lie outside a specified volume. The
exact effect of clipping some output primitives may be implementation or
workstation dependent.
color index
An index used to access an entry in a color table.
color model
Characterization of a color space in terms of explicit parameters.
color space
Geometric representation of colors in space, usually of three dimensions.
color spline
The parametric curve or surface in color space (or homogeneous color space)
defining the color distribution over an output primitive.
color system
A color coordinate system.
color table
A workstation dependent table, in which the entries specify the values defining
a particular color.
composite modelling transformation
A transformation applied to output primitives produced during structure
traversal. It is defined as the concatenation of the local modelling
transformation and global modelling transformations such that the local
modelling transformation is the first transformation to be applied.
conflict resolution flag
During the process of structure archiving from the CSS or structure retrieval
from an archive, naming conflicts may occur between structures on the archive
file and structures in the CSS. The conflict resolution flag indicates how
these conflicts will be resolved.
connection identifier
An implementation specific means of defining the connection to one or more
physical entities which constitutes a single workstation.
concentration exponent
A parameter of a spot light source that specifies the relative decrease of
light as the angle of the light deviates from the centreline of the light
source's cone of influence.
cone of influence
A conceptual cone that represents the influence of light from a spot light
source. The cone of influence is defined by the light source's position,
direction and spread angle.
data mapping
The conversion of application-specific data or color to intrinsic color.
data record
A compound data type, the content of which is defined by the context within
which it is used. For example, the content of the data records used in the
input device initialization functions may vary depending upon the particular
prompt and echo type specified in the invocation of the initialization
function.
deferral mode
The deferral mode for a workstation is part of the display update state and
specifies when changes to posted structure networks and the workstation state
list shall be reflected in the displayed image.
depth cueing
An effect in which the colors of points on an output primitive are combined
with a specified depth cue color. The degree of combination is dependent on the
depth (NPC Z) of the points.
depth cue mode
A field in each entry of the depth cue table of the workstation state list that
indicates whether or not depth cueing be performed.
depth cue table
A table in the workstation state list that contains information used to control
depth cueing.
descendant structure
A child structure or the descendant of a child structure.
device coordinates (DC)
A device dependent part of a PHIGS, DC units are metres on a device capable of
producing a precisely scaled image, and appropriate workstation dependant units
otherwise.
device driver
The device dependent part of a PHIGS implementation that supports a physical
graphics device. The device driver generates device dependent output and
handles device dependent interaction.
device space
The space defined by the addressable points of a display device. (Taken from
ISO 7942 and ISO 8805).
diffuse reflection
An approximation of the light reflected equally in all directions from an area.
Diffusely reflected light, in the absence of any specularly reflected light,
gives an area a dull, matte appearance that is independent of the viewing
direction.
diffuse reflection coefficient
The fraction of light from non ambient light sources diffusely reflecting from
an area.
direct color specification
A non-indexed method of specifying color where the components of the color,
i.e., coordinates in color space, are specified together with the color model
in which those components are expressed.
directional light
A light that enters into reflectance calculation dependent on the orientation
of the area being illuminated, but independent of the area's position.
Directional light sources are used to simulate light sources relatively far
from the area being lit.
display device
A graphics device on which images can be represented. A display device is one
possible component of a workstation.
display priority
The priority assigned to a structure network when it is posted. It is used to
discriminate between output primitives when they are mapped to the same display
space location.
display space
That portion of device space corresponding to the volume available for
displaying images.
display surface
The physical area on a display device onto which PHIGS images may be placed.
display update state
Determines how and when the display surface is modified to reflect changes in
the centralized structure store and the workstation state list. An application
selects the display update state to take into account the capabilities of a
workstation and the requirements of the application program. The display update
state consists of the two workstation dependent aspects of deferral mode and
modification mode.
echo
The immediate notification to the operator of the current measure of a logical
input device.
echo area; echo volume
An area or volume, defined in device coordinates, which may be used for the
display of a prompt or echo.
echo type
A parameter of device initialization which selects the echo technique for a
particular logical input device.
edge
The set of boundaries of the polygons defined in the fill area set output
primitive.
edge flag
An aspect on fill area set which enables or disables the display of edges.
edgetype
An aspect of fill area set which indicates the style of the edges.
edge visibility flag
An indicator that is part of the specification of some output primitives, such
as fill area set with data, that controls whether an individual edge is
visible. This indicator is only used during traversal when the edge flag aspect
is ON.
edge visibility flag
An indicator that is part of the specification of some output primitives, such
as fill area set with data, that controls whether an individual edge is
visible. This indicator is only used during traversal when the edge flag aspect
is ON.
edgewidth scale factor
An aspect of fill area set which indicates the relative width of the image of
an edge. The edgewidth scale factor is applied to a workstation dependent
nominal value.
edit mode
Determines whether a new structure element will replace the structure element
at the element pointer or will be inserted into the open structure after the
element pointer.
element pointer
A pointer used during structure editing, the value of which identifies the
position in the open structure at which element deletion and creation will
occur.
element position
A number associated with a structure element which indicates the element's
position within a structure.
element reference list
A list of references which define the hierarchy within one branch of a
structure network. Each reference consists of a structure identifier and an
element position within that structure. If the list contains N pairs, then the
first N-1 pairs identify EXECUTE STRUCTURE elements. The jth such element
references the structure named in the (j-1)st list element. The deepest element
of the list may identify any type of structure element.
element type
The identifying classification of a structure element. For example, fill area,
label, application data, linewidth scale factor.
empty interior style
One possible representation of the interior of a fill area or fill set output
primitive. If the edges are not displayed, the image of a fill area set with
interior style empty is invisible. The image of a fill area output primitive
with interior style empty is always invisible.
escape
A function which provides access to implementation dependent or device
dependent features not concerned with the generation of graphical output.
event mode
An operating mode for a logical input device in which asynchronous input is
placed or the event queue as an event report when a trigger fires.
event queue
A time-ordered collection of event reports.
event report
An entry in the event queue which consists of a logical input value and
identification of the logical input device responsible.
exclusion set
The portion of a filter which defines those name set members which are not
eligible for a certain operation.
eye point
A point in WC that transforms to infinite positive Z in NPC (the homogeneous
point (0, 0, 1, 0)). This point in the reflectance calculation for determining
viewing-position-dependent effects of lighting.
face culling
The process of excluding back facing or front facing portions of area
primitives from rendering pipeline, and thus from being displayed.
facet
An interior segment of an area primitive. Each of an output primitive is
defined by a subset of the primitive's set of vertices ; the subset is
dependent on the individual primitive type, and in the case of parametric
surfaces, on the approximation of the surface.
facet data
Intrinsic color data or a normal vector specified with an area primitive.
facet normal
A normal vector associated with a facet of an primitive. A facet normal is
typically used for determining the reflectance normal.
fill area
An output primitive consisting of a single polygon.
fill area set
An output primitive consisting of a set of fill areas with or without edges.
fill area set with data
An output primitive consisting of a set of coplanar polygons. It is similar to
the fill area set output primitive in Part 1. The corresponding structure
element may include other information such as colors or normals that may be
used to color, light and shade the output primitive.
filter
The combination of the inclusion set and the exclusion set which identify
output primitives eligible or ineligible for a certain operation. PHIGS
supports filters for picking, highlighting, invisibility, and incremental
spatial search.
font
A set of character representations all of which share certain visual
characteristics.
front facing
An adjective used to describe a portion of an area primitive that has a
geometric normal which, when transformed to NPC, has a non-negative Z.
front plane
A plane parallel to the view plane which is specified as an N coordinate value
in the view reference coordinate system. Output primitives in front of the
front plane lie outside the view volume.(Taken from ISO 8805).
general color
A data type that allows both the direct and indirect specification of color.
General color specifies a color type and color values. The color type can
either indicate a color model, in which case the color values are coordinates
in the color space corresponding to that model, or it can indicate that the
color is being indirectly, in which case the single color values is an index
into the workstation-dependent color table.
generalized drawing primitive (GDP)
An output primitive which accesses implementation dependent and workstation
dependent geometric capabilities such as curve drawing.
generalized structure element (GSE)
A structure element which is used to access implementation dependent,
workstation dependent, or device dependent features during structure traversal.
It is a structure element which access attribute or control functionality, but
does not create an output primitive.
geometric normal
A unit length vector that indicates the orientation of portions of area
primitives.
geometry spline
The parametric curve of surface defining the geometry of a parametric output
primitive.
global modelling transformation
A component of the composite modelling transformation. When traversal of a
structure begins, it is set to the current composite modelling transformation
of the parent structure or if it is the posted structure, the default value in
the PHIGS description table.
hatch interior style
One possible representation of the interior of a fill area set or fill area
output primitive. The interior is filled with a pattern of parallel and/or
crossing hatch lines, selected from the workstation's hatch table.
hidden line/hidden surface removal (HLHSR)
Removal of those parts of output primitives which are obscured by other output
primitives.
highlighting
Emphasizing an output primitive by modifying its visual attributes in some
workstation dependent manner.
highlighting filter
A filter consisting of two name sets, the highlighting inclusion set and the
highlighting exclusion set, used to identify output primitives which are
eligible for highlighting.
HLS
An abbreviation of the Hue, Lightness, Saturation color model.
hollow interior style
One possible representation of the interior of a fill area or fill area set
output primitive. The image is the boundary line only, including any boundaries
created by clipping.
HSV
An abbreviation for the Hue, Saturation, Value color model.
image
The appearance of objects after rendering.
implicit regeneration
The complete recreation of the contents of a display surface such that it is
visually correct. This may occur when changes to the posted structure networks
or the workstation state list invalidate the displayed image. Such a
regeneration is not explicitly requested by the application program.
inclusion set
The portion of a filter which defines those name set members eligible for a
certain operation.
indirect color specification
A method of specifying color via an index into a workstation dependent color
table.
inheritance
The mechanism by which child structures obtain initial attribute settings from
their ancestor structures.
input class
The characterization of the functionality of a logical input device. There are
six classes of logical input device : locator, stroke, valuator, choice, pick,
and string.
input mode
One of the three possible methods of obtaining data from a logical input device
: REQUEST, SAMPLE, or EVENT.
inquire function
A mechanism for communicating to the application program data contained in a
state list or description table.
interior
The set of points which lie inside a fill area set. PHIGS provides a rule for
determining whether or not a given point is inside a fill area or fill area
set.
interior style
An aspect which indicates the style used to fill the interior of a fill area or
fill area set.
intrinsic color
The color of an output primitive that are independent of lighting, depth cueing
an color mapping.
invisibility
The state if an output primitive being hidden from view even when lying within
the display surface and not occluded by other output primitives.
invisible filter
A filter consisting of two name sets, the invisibility inclusion set and the
invisibility exclusion set, used to identify output primitives eligible for
invisibility.
intrinsic color data
Color or application-specific data associated with output primitives and
specified in the output primitive's structure element. Intrinsic color data,
when specified, is conditionally used to determine the intrinsic color of an
output primitive.
isoparametric curve
A curve on a parametric surface produced by evaluating the surface over the
range of one of its independent variables while holding its other independent
variable constant.
isotropic mapping
A transformation which preserves aspect ratio.
knot vector
A non decreasing sequence of real numbers that is part of the definition of
non-uniform B-splines. This vector consists of values for the independent
variables of the output primitive and is used in computing the B-spline basis
polynomials.
label
A structure element, consisting of an identifier, which can be used as a
place-marker to facilitate structure editing.
language binding
The expression of a functional specification in the syntax of a particular
programming language.
light source
An entry in a workstation light source table used to simulate a source of
light. All light sources have a color. Some light source types have aspects
such a position, direction, concentration exponent, spread angles and
attenuation.
light source direction
A unit vector that defines the orientation of oriented light sources.
light source state
A field in the traversal state list that selects which light sources in a
workstation light source table are active.
lighting
See reflectance calculation.
linetype
An aspect which indicates the style of the images of a polyline, such as solid,
dashed or dotted.
linewidth scale factor
An aspect which indicates the relative width or the image of a polyline. The
linewidth scale factor is applied to a workstation dependent nominal value.
local modelling transformation
A component of the composite modelling transformation. When traversal of a
structure begins, it is set to the identity transformation.
locator device
A logical input providing a position in world coordinates and an associated
view index.
logical input device
An abstraction of one or more physical input devices which delivers logical
input values to the application program.
marker
A glyph with a specifies appearance which is used to identify a location on a
display surface. The shape of a marker us not subject to transformation
marker size scale factor
An aspect which indicates the relative size of the image of a marker. The
marker size scale factor is applied to a workstation dependent nominal value.
marker type
An aspect which selects the type of glyph used for markers.
measure
A value which is determined by the values of one or more physical input devices
and a mapping from these values to a form required by one of the logical input
classes. (Taken from ISO 7942 and ISO 8805).
measure process
A process which comes into existence when a logical input device is enabled for
interaction. The current state of a measure process is the measure.
message
A string sent b the application program to a workstation principally for
communication with the operator.
metafile
A mechanism for retaining and transporting graphical data and control
information. A metafile contains a device independent description of one or
more pictures. (Taken from ISO 8632).
minimal simulation
The minimal required action which is necessary when a workstation does not have
the capability to render an output primitive as specified by the application.
modal
A type of change mechanism which extends its effect until another change
specification supersedes it. Attribute settings and control functions are modal
for a given structure and its descendant structures.
modelling coordinates
The device independent three-dimensional Cartesian coordinate system in which
graphical objects are defined by the application program using the PHIGS output
primitives
modelling transformation
See local modelling transformation, global modelling transformation, composite
modelling transformation.
modification mode
Part of the display update state. The modification mode governs what category
of visual effects shall be immediately achieved, and how they are achieved, on
a workstation.
name set
An output primitive attribute consisting of a set of classifications defining
the eligibility of output primitives for highlighting, invisibility, picking
and incremental spatial search.
nominal value
The workstation dependent base value for aspects of output primitives.
normal vector
A unit length vector, typically indicating the orientation of an object
([section] 6.2).
normalized projection coordinates (NPC)
The device independent three-dimensional Cartesian coordinate system in which
the composition of images is specified to the graphics system. The view
clipping limits and the workstation window are specified in NPC space.
operator
Person manipulating physical input devices so as to change the measures of
logical input devices and cause their triggers to fires. (Taken from ISO 7942
and ISO 8805).
output primitive
A fundamental graphical display entity representing a geometric shape.
parallel transformation
The transformation of an object in which parallel lines in the object appear
parallel in the resulting image without regard to relative distance or depth.
(Taken from ISO 8805).
parameter range
The parameter space over which a parametric curve or surface is
defined.
parameter range limits
Minimum and maximum parameter values, specified separately from any knot
values, that limit the parameter range over which parametric curves are
generated.
parametric output primitive
output primitives defined as a mapping from parameter space to modelling
coordinates. Parametric output primitives defined in GPHIGS PLUS are
non-uniform B-spline curve, non-uniform B-spline surface data.
parameter space
The coordinate system of the independent variable(s) of parametric curves and
surfaces, one dimensional for curves and two-dimensional for surfaces.
parent structure
A structure which contains one or more structure references.
pattern interior style
One possible representation of the interior of fill area set output primitive.
The interior is filled in with a two-dimensional pixel pattern selected from
the workstation's pattern table.
pattern table
The table of the pattern values defined on a workstation.
perspective transformation
The transformation of an object in which parallel lines in the object which
intersect the view plane appear to converge in the resulting image as a
function of relative distance or depth. (Taken from ISO 8805).
PHIGS
The programmer's Hierarchical Interactive Graphics System.
PHIGS description table
The data which represents the static workstation independent parameters of a
PHIGS system.
PHIGS state list
The data which represents the dynamic workstation independent parameters of a
PHIGS system.
PHIGS traversal state list
The data which represents the dynamic workstation independent parameters of a
PHIGS system during traversal of a structure network. When traversal begins the
PHIGS traversal state list values are set to the values defined in the PHIGS
description state.
physical input device
Hardware capable of generating input. A physical input device is either part of
a display device or a separate part of the workstation.
picking
An operator action of identifying an output primitive using a pick device.
pick device
A logical input device providing a pick path.
pick filter
A filter consisting of two name sets, the pick inclusion set and the pick
exclusion set used to identify output primitives which are eligible for
selection by a pick input operator.
pick identifier
A name associated with individual output primitives, and returned by a pick
device as a component of the pick path.
pick path
The element reference list representing a path to a picked output primitive
from its posted structure, consisting of the structure identifier, pick
identifier and element position for each level of hierarchy traversed.
polyline
An output primitive consisting of a connected sequence of straight lines
between specified points.
polyline set with data
An output primitive consisting of an unconnected set of polylines. The
corresponding structure element may include color information that may be used
to shade the primitive.
polymarker
An output primitive consisting of a set locations, each indicated by the same
type of marker.
positional light
A light source that enters into reflectance calculation dependent on the
orientation and position of an area being illuminated relative to the light
source.
post
To identify a structure network for display on a particular workstation.
projection reference point (PRP)
A point in view reference coordinate space which determines the direction of
projectors when the projection type is PARALLEL, or from which all projectors
emanate when the projection type is PERSPECTIVE.
projection type
The type of transformation to be used in view mapping, i.e., parallel
transformation or perspective transformation.
projection viewport
A rectangular parallelepiped in normalized projection coordinate space. In the
PHIGS view model, the view mapping transformation maps the contents of the view
volume into the projection viewport.
projector
A conceptual line which passes through a point of an object and intersects the
view plane.
prompt
Output to the operator indicating that a specific logical input device is
available.
pseudo color mapping
A color mapping method that uses a weighted average of the color coordinates to
produce an index into a table of colors.
pseudo-N color mapping
A color mapping method that uses each coordinate of a color as an index into
one of a number of separate list of color components. The combination of these
components define the color used for display.
quadrilateral mesh
An output primitive in which an array of quadrilaterals is specified by a two
dimensional array of points.
reflectance calculation
The computation of the effect of light sources on a portion of an output
primitive.
reflectance model
An aspect that selects the reflectance calculation and thereby specifies what
lighting effects may be displayed.
reflectance formulae
Formulae that model the light reflected by an area primitive.
reflectance normal
A vector, conceptually perpendicular to some portion of an area primitive, that
indicates the orientation of that portion. It typically influences the
reflectance calculation and is derived from vertex normals or other geometry of
the output primitive.
reflectance properties
An aspect of area primitives that indicates how a primitive reflects light.
rendering color model
The color model used for performing color interpolation within the rendering
pipeline.
rendering pipeline
A sequence of operations that performs data mapping, lighting, shading, depth
cueing, and color mapping of output primitives. Each of these operations is
considered a stage in the pipeline.
request mode
An operating mode for a logical input device in which PHIGS waits until the
operator activates the appropriate trigger where upon the measure is
returned.
RGB
An abbreviation for the Red, Green, Blue color model.
sample mode
An operating mode for a logical input device in which the measure of a logical
input device may be obtained immediately without waiting for a trigger.
set of fill area set with data
An output primitive in which a number of possibly non-coplanar fill area sets
are defined by indices into a single vertex list; The fill area are not
required to form a closed or connected surface.
shading
The interpolation portion of the rendering pipeline.
solid interior style
One possible representation of the interior of a fill area or fill area set
output primitive. The interior is filled with a uniform color.
specular color
The color of specular highlights on an area primitive.
specular exponent
A non-negative number indicating the shininess of an area. The higher the
specular exponent, the shinier the area. A specular exponent of 0 indicates a
minimum relative degree of shininess.
specular reflection
An approximation of the unequal reflection of light in different directions
from an area primitives. The intensity of specular reflections, unlike diffuse
reflections, is dependent on the viewing angle of the observer.
specular reflection coefficient
The fraction of non-ambient light contributing to specular reflection.
spot light
A light source that enters into the reflectance calculation dependent on the
orientation and relative position of the area being illuminated. Light from
such a source is restricted to a semi-infinite cone of influence and its
intensity is possibly modified as its deviates from the centreline of this
cone. (See concentration exponent).
spread angle
An angle that determines the shape of the cone of influence of a spot light
source. Spread angles is the angle between the spot light source direction
vector and the limit of the cone of influence measured at the position of the
spot light source.
string
An ordered collection of character codes.
string device
A logical input device providing a string.
stroke device
A logical input device providing a sequence of points in world coordinates, and
associated view index.
structure
A linear sequence of structure elements.
structure archiving
The process of storing structures and structure networks in an archive file for
subsequent structure retrieval.
structure editing
The modification of structure, including its initial creation
structure element
The fundamental unit of data in the centralized structure store, a sequence of
which is collected to form a structure. Structure elements include elements
causing the generation of output primitives, attribute selections, labels,
application data, NAME SET specifications, transformation selections and
structure references.
structure identifier
A unique application specified name used to reference a structure.
structure network
A collection of structures arranged with the topology of an acyclic directed
graph, where structures are thought of as nodes and execute structure elements
are thought of as connections from the parents structure et the child
structure.
structure reference
The invocation of one structure from within another by an execute structure
element or the invocation of a structure by posting.
structure retrieval
The process of copying structured from an archive file to the centralized
structure store.
structure state list
The data which represents information about each structure in the centralized
structure store.
text
An output primitive consisting of a character string drawn at a specified
position on a specified text plane.
text alignment
An aspect of text which specifies the mode of justification. This aspect has
horizontal and vertical components.
text direction vectors
Two vectors, specified as part of the "text" structure element, which, together
with the text position, define the text plane.
text extent
A parallelogram defining the minimum area which completely encloses the
character bodies in a string.
text front
An aspect of text which indicates certain visual properties of a character,
such as typeface.
text local coordinate system
The local coordinate system for text output primitives within which all
geometric text attributes are measured.
text path
An aspect of text which controls the relative positioning of successive
characters in a string.
text plane
The plane in which a text output primitive appears.
text position
A point, specified as part of the "text" structure element, which, together
with the text direction vectors, determine the text plane. It also determines,
together with text alignment, the location of the string.
text precision
An aspect of text which selects the fidelity with the drawing of a text output
primitive matches the appearance selected by an application program.
transformation pipeline
The ordered sequence of transformations which convert modelling coordinates to
device coordinates.
traversal
The process of stepping through a structure network, elaborating each structure
element by generating an output primitive or changing the state list.
traversal state list
See PHIGS traversal state list.
triangle set
An output primitive in which a number of, possibly unrelated, triangular facets
are defined by indices into a single vertex list.
triangle strip
An output primitive in which N - 2 triangles are defined by N
points.
trigger
A physical input device or set of devices that an operator can use to indicate
significant moments in time.
trigger process
A process which notifies an associated logical input device when a trigger is
fired. The trigger process only exists when a device is in EVENT, or in REQUEST
mode with a request pending.
trimmed surface
A non uniform B-spline surface whose specification contains a set of trimming
loops that limit the range of the independent variables over which the surface
is evaluated. (See also trimming loop).
trimming curve
A parametric curve in the parameter space of the surface to which it applies.
Trimming curves are combined to form trimming loops which limit the parameter
range over which a parametric surface is evaluated.
trimming loop
A sequence of connected and similarly oriented trimming curves that form a
closed path. Trimming loops are used to limit the parameter range over which a
parametric surface is evaluated.
unpost
To remote the identification of a structure for display on a particular
workstation.
valuator device
A logical input device providing a real number.
vertex color
A general color associated with each vertex of some types of output primitives.
Examples of such output primitives are polyline set with data and fill area set
with data. This color may be used within the rendering pipeline to color and
shade the primitive.
vertex data
geometric, intrinsic color or vertex normal data specified at vertices of
certain output primitives. This data specifies the geometry of an output
primitive and, depending on various attribute settings, is used to influence
the appearance of a primitive.
vertex normal
A normal vector optionally supplied with the vertex data of some area
primitives.
view index
An output primitive attribute that selects the view representation applied to
output primitives and geometric attributes during structure traversal.
view mapping matrix
A 4*4 matrix which specifies the transformation of points from view reference
coordinates to normalized projection coordinates.
view orientation matrix
A 4*4 matrix which specifies the conversion of points from world coordinates to
view reference coordinates.
view plane
A plane parallel to the U.V plane in view reference coordinate space (VRC). It
is specified as an N coordinate value in VRC.
view plane normal
A vector in world coordinates, relative to the view reference point, which
defines the N coordinate axis of the view reference coordinate system.
view reference coordinate (VRC) system
A device independent three-dimensional Cartesian coordinate system in which the
parameters for the view mapping transformation are specified. The axes of the
view reference coordinate system are called the U.V and N axes. The position
and orientation of this coordinate system, relative to world coordinates, are
defined by the view reference point, the view plane normal and the view up
vector.
view reference point
A point in world coordinates which defines the view reference coordinate system
origin.
view representation
A single entry in the view table. it consists of the view orientation matrix,
the view mapping matrix, the view clipping limits and a set of clipping
indicators.
view table
The table of view representations defined on a workstation. Its entries are
reference by the view index attribute.
view transformation input priority
Determines the order in which view table entries are tested when selecting the
inverse viewing transformation to be applied to locator and stroke input.
view up vector
A vector defined in world coordinate space. The view reference coordinate
system V coordinate axis is defined as an orthogonal projection of the view up
vector onto the plane through the view reference point and perpendicular to the
view plane normal. Vectors which are parallel to the view up vector in world
coordinate space will appear vertical in the final image.
view volume
The view volume is determined by the view window defined in the view plane, the
front plane, the back plane, and projectors through the corners of the view
window. If the projection type is PERSPECTIVE, the projectors all pass through
the projection reference point, the view volume is therefore a frustum. If the
projection type is PARALLEL, the projectors are parallel to the vector joining
the projection reference point to the centre of the view window, the view
volume in this case is a parallelepiped. In two dimensional application
programs, the view volume reduces to the view window. (Taken from ISO 8805).
view window
A rectangle in the view plane. Projectors passing through the corners of the
view window define the left, right, bottom and top surfaces of the view
volume.
visual correct
The display on a workstation is visually correct when it corresponds exactly to
the state of centralized structure store and the workstation state list.
with-data primitives
Any of the output primitives : fill area set with data, set of fill area set
with data, triangle set with data, triangle strip with data, quadrilateral mesh
with data and non-uniform B-spline surface with data. In addition, some
generalized drawing primitives may have this classification.
workstation
PHIGS is based on the concept of abstract graphical resources, which provide
the logical interface through which the application program controls physical
devices. A workstation consists of zero or one display space and zero or more
logical input devices.
workstation category
A property of a workstation which indicates whether it can perform graphics
input only, graphics output only, or both.
workstation description table
The data which represents capabilities for a particular workstation type.
workstation identifier
A unique application specified name used to identify a particular
workstation.
workstation state list
The data which represents dynamic information for a particular workstation.
workstation transformation
A transformation which maps the contents of the workstation window into the
workstation viewport, preserving aspect ratio in X and Y, but not necessary in
Z.
workstation type
A type or class of actual workstation, sharing common characteristics and a
single workstation description table.
workstation viewport
A rectangular parallelepiped in device coordinate space. All graphics output
appears within this volume.
workstation window
A rectangular parallelepiped in normalized projection coordinate space. Its
contents are mapped by the workstation transformation into the workstation
viewport. (Taken from ISO 8805).
world coordinates (WC)
The device independent three-dimensional Cartesian system used by the
application program to organize modelled objects for display. The effect of
applying the composite modelling transformation to modelling coordinates is to
produce world coordinates.
G5G - GPHIGS USER GUIDE