EN ISO/IEC 9592-4:1996

SLOVENSKI STANDARD
01-januar-1998
Information processing systems - Computer graphics - Programmer's Hierarchical
Interactive Graphics System (PHIGS) - Part 4: Plus Lumiere und Surfaces, PHIGS
PLUS (ISO/IEC 9592-4:1992, including Technical Corrigendum 1:1994)
Information processing systems - Computer graphics - Programmer's Hierarchical
Interactive Graphics System (PHIGS) - Part 4: Plus Lumiere und Surfaces, PHIGS PLUS
(ISO/IEC 9592-4:1992, including Technical Corrigendum 1:1994)
Systemes de traitement de l'information - Infographie - Interface de programmation du
systeme graphique hiérarchisé (PHIGS) - Partie 4: Plus Lumiere und Surfaces, PHIGS
PLUS (ISO/IEC 9592-4:1992, Rectificatif Technique 1:1994 inclus)
Ta slovenski standard je istoveten z: EN ISO/IEC 9592-4:1996
ICS:
35.140 5DþXQDOQLãNDJUDILND Computer graphics
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

ISO/IEC
I N TE R NAT1 O NA L
9592-4
STANDARD
First edition
1992-09-01
Information processing systems - Computer
graphics - Programmer% Hierarchical
Interactive Graphics System (PHIGS) --
Part 4:
Plus Lumière und Surfaces, PHIGS PLUS
Syst&mes de traitement de l’information -- lnfographie - lnterface de
programmation dlJ système graphique hiérûrchis4 (PH/GS) -
Partie 4: Plils Lumiére und Surfaces, PHlGS PLUS
Reference number
ISQ/IEC 9592-4: 1992( E)
ISO/IEC 9592-4:1992(E)
Contents Page
1 scope . 1
2 Normative references . 2
3 Definitions . 3
4 The PHIGS PLUS system . 7
4.1 About this part of ISO/IEC 9592 . 7
4.1.1 Specification and conformance . 7
4.1.2 Regismtion . 7
4.1.3 Notational conventions . 7
4.2 Overview and concepts . 8
4.2.1 Overview . 8
4.2.2 Concepts . .8
4.3 PHIGS PLUS structure elements . 10
4.3.1 Output primitive structure elements . 10
4.3.2 Attribute specification structure elements . 10
4.3.3 Structure element archive . 11
4.4 Output primitives . 12
4.4.1 General . 12
4.4.2 Polyline set with colour . 12
4.4.3 Fill area set with data . 12
4.4.4 Cell array PLUS . 13
4.4.5 Set of fill area set with data . 13
4.4.6 Triangle set with data . 13
4.4.7 Triangle strip with data . 13
4.4.8 Quadrilateral mesh with data . 14
4.4.9 Non-uniform B-spline curve . 14
4.4.10 Non-uniform B-spline curve with colour . 16
4.4.11 Non-uniform B-spline surface . 16
4.4.12 Surface trimming . 17
4.4.13 Non-uniform B-spline surface with data . 18
4.4.14 Area primitives and facets . 20
4.4.15 Modelling clip . 20
4.5 Output primitive attributes . 21
4.5.1 General colour specification . 21
4.5.2 Extended workstation state and description tables . . 22
4.5.3 PHIGS PLUS attributes applied to PHIGS output primitives . 23
4.5.3.1 General . 23
4.5.3.2 Polyline attributes . 25
4.5.3.3 Polymarker attributes . 25
4.5.3.4 Text attributes . 25
4.5.3.5 Annotation text attributes . 25
4.5.3.6 Fill area attributes . 26
4.5.3.7 Fill area set attributes . 26
Q ISOllEC 1992
All rights reserved . No part of this publication may be reproduced or utilized in any form
or by any means. electronic or mechanical. including photocopying and tnicrofilrn. without
permission in writing from the publisher .
ISOllEC Copyright Office Case Postale 56 * CH-1211 Genève 20 Switzerland
Printed in Switzerland
ii
ISO/IEC 9592-4:1992(E)
4.5.3.8 Cell array attributes . 26
4.5.3.9 Generalized drawing primitive attributes . 26
4.5.4 Attributes applied to PHIGS PLUS output primitives . 27
4.5.4.1 General . 27
4.5.4.2 Polyline set with colour attributes . 27
4.5.4.3 Fill area set with data attributes . 27
4.5.4.4 Cell array PLUS attributes . 27
4.5.4.5 Set of fill area set with data attributes . 27
4.5.4.6 Triangle set with data attributes . 27
4.5.4.7 Triangle strip with data attributes . 27
4.5.4.8 Quadrilateral mesh with data attributes . 27
4.5.4.9 Non-uniform B-spline curve attributes . 31
4.5.4.10 Non-uniform B-spline curve with colour attributes . 32
4.5.4.11 Non-uniform B-spline surface attributes . 33
4.5.4.12 Non-uniform B-spline surface with data attributes . 36
4.5.4.13 Individual edge control for PHIGS PLUS area primitives . 36
4.5.4.14 Reflectance properties . 36
4.5.5 Implicitly specified attributes . 37
4.5.5.1 General . 37
4.5.5.2 Facet normal . 37
4.5.5.3 Facet orientation . 38
4.5.5.4 Reflectance normal . 38
4.5.5.5 Intrinsic colour . 39
4.5.6 Facet culling . 40
4.5.7 Distinguishing facets by orientation . 40
4.5.8 Hidden line and hidden surface removal . 40
4.5.9 Stability . 40
4.6 The PHIGS PLUS rendering pipeline . 41
4.6.1 General . 41
4.6.1.1 Primitives affected by the rendering pipeline . 41
4.6.1.2 The effect of the interior style on lighting and shading . 41
4.6.1.3 Aspects and attributes used in the rendering pipeline . 42
4.6.2 Data mapping . 42
4.6.3 Lighting . 47
4.6.3.1 Reflectance calculation . 47
4.6.3.2 Light sources . 48
4.6.3.3 Workstation light sources . 48
4.6.4 Shading . 49
4.6.4.1 General . 49
4.6.4.2 Interpolation . 49
4.6.4.3 Colour interpolation . 49
4.6.4.4 Data interpolation . 50
4.6.4.5 Normal-vector interpolation . 50
4.6.4.6 Polyline shading . 50
4.6.4.7 Interior shading . 50
4.6.5 The rendering colour modcl . 53
4.6.6 Depth cueing . 54
4.6.7 Colour mapping . 55
4.7 Workstations . 57
iii
ISO/IEC 9592-4: 1992(E)
4.8 Graphical input . 58
4.9 Limitations . 59
4.9.1 General . 59
4.9.2 Non-planar geometry and data . 59
4.9.3 Relationship of shading method to geometry . 59
4.9.4 Normal-vector interpolation . 59
4.9.5 Effects of transformations . 59
4.9.6 Approximation criteria and data splines . 60
4.10 Minimum support criteria . 61
5 PHIGS PLUS Functional Specification . 65
5.1 Notational Conventions . 65
5.2 Output primitive functions . 65
5.3 Attribute specification functions . 82
5.3.1 Bundled attribute selection . 82
5.3.2 Individual attribute selection . 84
5.3.3 Aspect source flag setting . 99
5.3.4 Workstation attribute table definition . 100
5.4 inquiry functions . 112
5.4.1 Introduction . 112
5.4.2 Inquiry functions for workstation state list . 113
5.4.3 Inquiry functions for workstation description table . 123
5.4.4 Inquiry functions for structure content . 138
6 PHIGS PLUS data structures . 143
6.1 General . 143
6.2 Notation and Data Types . 143
6.3 PHIGS PLUS additions and replacements to the PHIGS description table . 144
6.4 PHIGS PLUS additions and replacements to the PHIGS traversa1 state list . 146
6.5 PHIGS PLUS additions and replacements to the PHIGS workstation state list . 148
6.6 PHIGS PLUS additions and replacements to the PHIGS workstation descriplion table . 151
Annex A Function lists . 155
A.l Alphabetic . 155
A.2 Order of appearance . 157
Annex B Error list . 161
B.l Implementation dependent . 161
B.2 Output attributes . 161
B.3 Output primitives . 161
Annex C Suggested reflectance formulae . 163
C.1 Variable definitions and their sources . 163
C.2 Reflectance formulae . 164
Annex D Allowable differences in PHIGS PLUS implementalions . 167
D.1 Introduction . 167
D.2 Workstation dependent differences . 167
Annex E Suggested depth cueing formulae . 169
E.l Linear colour interpolation . 169
E.2 Definitions . 169
E.3 Formulae . 169
Annex F Attribute table . 171
iv
ISOhEC 9592-4:1992(E)
r
%4
Foreword
IS0 (the International Organization for Standardization) and IEC (the
International Electrotechnical Commission) form the specialized system
for worldwide standardization. National bodies that are members of IS0
or IEC participate in the development of International Standards through
technical cornmittees established by the respective organization to deal
with particular fields of technical activity. IS0 and IEC technical com-
mittees collaborate in fields of mutual interest. Other international or-
ganizations, governmental and non-governmental, in liaison with IS0
and IEC, also take part in the work.
In the field of information technology, IS0 and IEC have established a
joint technical committee, ISO/IEC JTC 1. Drafi International Standards
adopted by the joint technical committee are circulated to national bod-
ies for voting.
Publication as an International Standard requires ap-
proval by at least 75 Oh of the national bodies casting a vote.
International Standard ISO/IEC 9592-4 was prepared by Joint Technical
Committee IÇOAEC JTC 1, lnformation technology.
ISO/IEC 9592 consists of the following parts, under the general title ln-
formation processing systems - Computer graphics - Programmer's
Hierarchical Interactive Graphics System (PHIGS):
-- Part 1: Filnctional description
-- Part 2: Archive file format
- Pari 3: Clear-fexf encoding of archive file
- Pari 4: Plus Lumière und Surfaces, PHlGS PLUS
Annex D forms an integral part of this part of iSO/IEC 9592. Annexes A,
B, C, E and F are for information only.

ISO/IEC 9592-4:1992(E)
In t reduction
ISO/IEC 9592-1 provides a set of functions for the definition, display and modification of 2D or 3D graphical data. It does
not provide support for simulating the effects of lighting, shading, and other properties that are important for the display
data. This part of ISODEC 9592 specifies a basic set of such functionality for use in conjunction with
of multi-dimensional
the functionality defined in ISODEC 9592-1 and its amendment 1.
To provide this support, PHIGS PLUS defines
a) output primitives specified by rational and non-rational B-spline curves and surfaces;
b) output primitives containing both geometric and non-geometric data in their definition;
c) attributes that control the application of lighting and shading to both the new primitives and the primitives specified
in ISO/IEC 9592-1;
d) a generalized mechanism for colour specification to allow non-indexed colour specification.

INTERNATIONAL STANDARD ISO/IEC 9592-4:1992(E)
Information processing systems-
Computer graphics-
Programmer’s Hierarchical Interactive Graphics System
(PH1GS)-
Part 4-Plus Lumière und Surfaces, PHIGS PLUS
1 Scope
This part of ISO/IEC 9592 specifies an additional set of functionality of the Programmer’s Hierarchical Interactive
Graphics System. This additional functionality is intended to satisfy basic application requirements in the areas of
lighting and shading and defines additional primitives and functionality for controlling the rendering of 3D objects. It
relies on the coexistence of the functions and functionality specified in ISO/IEC 9592-1, and is meant to extend that func-
tionality in the above areas.
It is the intent of this part of ISO/IEC 9592 to be compatible with ISODEC 9592-1 and its Amendment 1. That is, in a stan-
dard conforming PHIGS PLUS implementation all functions defined in ISO/IEC 9592-1 and not altered by ISO/IEC 9592-4
shall perform as specified in ISODEC 9592-1, and all functions defined in ISO/IEC 9592-1 but altered in ISO/IEC 9592-4
shall perform as specified in ISO/IEC 9592-1 and ISODEC 9592-4, and, an application functionally conforming to
ISO/IEC 9592-1 produces the same effect running on a standard conforming PHIGS PLUS implementation as it would
pmduce running on a standard conforming PI-IJGS ISOiIEC 9592-1 impleineiitation, cxcepiing such differences among
implementations as are allowed in ISODEC9592-1. If PHIGS PLUS functions are used, they should only cause the
extended effects specified in this part of ISO/IEC 9592.
This part of ISODEC 9592 defines a language indcpcndcnt extension to a graphics system for integration into a program-
ming language. PHIGS PLUS is embedded in a language layer obeying the particular conventions of the language. Such
language bindings are specified for IS0 or ISO/IEC languages in ISOflEC 9593.
ISOhEC 9592-4: 1992(E)
2 Normative references
The following standards contain provisions which, through reference in this text, constitute provisions of this part of
ISOAEC 9592. At the time of publication, the editions indicated were valid. All standards are subject to revision, and
parties to agreements based on this part of ISOAEC 9592 are encouraged to investigate the possibility of applying the
most recent editions of the standards indicated below. Members of IEC and IS0 maintain registers of currently valid
International Standards.
ISODEC 646: 1991, Information technology - IS0 7-bit coded character setfor information exchange.
ISOAEC 7942: 1985, Information processing systems - Computer graphics - Graphical Kernel System (GKS)
functional description.
ISO/IEC 863211987, Information processing systems - Computer graphics - Metafile for storage and transfer of
picture description information.
ISOiIEC 8805: 1988, Information processing systems - Computer graphics - Graphical Kernel System for Three
Dimensions (GKS-3D) functional description.
ISOAEC 9592-1 : 1989, Information processing systems - Computer graphics - Programmer's Hierarchical Interactive
Graphics System (PHIGS) - Part I: Functional description.
ISOAEC 9592-1 : 1989iAmd. 1: 1992, Information processing systems - Computer graphics - Programmer's Hierarchi-
cal Interactive Graphics System (PHIGS) - Part I: Functional description -Amendment 1.
ISOAEC 9592-2: 1989, Information processing systems - Computer graphics - Programmer's Hierarchical Interactive
Graphics System (PHIGS) - Part 2: Archive$ie format.
ISOIIEC 9592-2: 1989iAmd. 1: 1992, Information processing systems - Computer graphics - Programmer's
Hierarchical Interactive Graphics System (PHIGS) - Part 2: Archive file format -Amendment I.
ISO/IEC 9592-3 : 1989, Information processing systems - Computer graphics - Programmer's Hierarchical Interactive
Graphics System (PHIGS) - Part 3: Clear text encoding of archive file.
TSO/IEC 9592-3: 1989iAmd. 1: 1992, Information processing systems - Computer graphics - Programmer's Hierarchi-
cal Interactive Graphics System (PHIGS) - Part 3: Clear text encoding of archive file -Amendment 1.
ISODEC 9593 : 1990, Information processing systems - Computer graphics - Programmer's Hierarchical Interactive
Graphics System (PHIGS) language bindings.
ISOhEC 9592-4: 1992(E)
3 Definitions
For the purpose of this part of ISO/IEC 9592 the following definitions apply. This part of ISO/IEC 9592 also makes use of
the definitions in ISO/IEC 9592-1. (Terms used within definitions in this clause that are themselves defined in this clause
are italicized.)
3.1 ambient light source: A light source that contributes to the reflectance calculation independently of the orientation
or position of the area being illuminated or the location of the viewer’s eye.
3.2 ambient reflection coefficient: The fraction of ambient light reflected from an area.
3.3 area primitive: Any of the output primitives: fill area, fill area set, cell array,fill area set with data, cell array PLUS,
set offill area sets with data, triangle set with data, triangle strip 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,
3.4 attenuation coefficient: A coefficient that determines the decrease in intensity of light as a function of the distance
between a light source and an illuminated object.
3.5 back facing: A back-facing facet has a facet normal that, when transformed to NPC, has a negative 2 component.
See also front facing.
3.6 colour mapping: The conversion of direct colours in the rendering pipeline to other colours before they are
displayed on the workstation.
3.7 colour spline: The parametric curve or surface in colour space (or homogeneous colour space) defining the colour
distribution over an output primitive.
3.8 concentration exponent: A parameter of a spof light source that specifies the relative decrease of light as the angle
of the light diverges from the centreline of the light source’s cone of influence.
3.9 cone of influence: A conceptual cone that represents the influence of light from a spot light source. The cone of influ-
ence is defined by the light source’s position, direction and spread angle.
3.10 data mapping: The conversion of application-specific data or colour to intrinsic colour.
3.11 depth cueing: An effect in which the colours of points on an output primitive are combined with a specified depth
cue colour. The degree of combination is dependent on the depth (Z in normalized projection coordinates) of the points.
3.12 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 should be performed.
3.13 depth cue table: A table in the workstation state list that contains information used to control depth cueing.
3.14 diffuse reflection: An approximation of the light reflected equally in all directions from an area.
3.15 diffuse reflection coefficient: The fiaction of light from non-ambient light sources that is diffusely reflecting from
an area.
3.16 direct colour specification: A non-indexed mcthod of specifying colour where the components of the colour, i.e.,
coordinates in colour space, are specified together with the colour model in which those components are expressed.
3.17 directional light source: A light source that contributes to the reflectance calculation dependent on the orientation
of the area being illuminated but independent of the area’s position.
3.18 edge visibility flag: An indicator that is part of the specification of some output primitives, such asfill area set with
data, that controls whether an individual edge is visible.
3.19 eye point: A point in world coordinates that transforms to infinite positive Z in normalized projection coordinates.
This point is used in the reflectance calculation for determining viewing-position-dependent effects of lighting.
3.20 facet: An interior segment of an area primifive. Each facet of an output primitive is defined by a subset of the prim-
itive’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. Facets have an orientation in NPC described as back-facing orfront-facing.
ISO/IEC 9592-4 1992(E)
3.21 facet culling: The process of removing front-facing or back-facing facets of area primitives.
3.22 facet data: Intrinsic colour data or a normal vector specified with an area primitive.
3.23 facet normal A normal vector associated with a facet of an area primitive. Facet normals are used to determine the
orientation of a facet and in some cases for determining the reflectance normal.
3.24 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 defined in ISOLEC 9592-1. The corresponding structure element may include other information such as
colours or normais that are conditionally used to colour, light and shade the output primitive.
3.25 front facing: A front-facing facet has a facet normal that, when transformed to NPC, has a positive or zero Z
component. See also backfacing.
3.26 general colour: A data type that allows both the direct and indirect specification of colour. General colour specifies
a colour type together with a type-dependent colour value. The colour type can either indicate a colour model, in which
case the colour values are coordinates in the colour space corresponding to that model, or it can indicate that the colour
is being specified indirectly, in which case the single colour value is an index into the workstation-dependent colour
table.
3.27 geometry spline: The parametric curve or surface defining the geomciry of a parametric output primitive.
3.28 indirect colour specification: A method of specifying colour via an index into a workstation dependent colour
table.
3.29 intrinsic colour: The colour or colours of an output primitive that are independent of lighting, depth cueing and
colour mapping.
3.30 intrinsic colour data: Colour or application-specific data associated with output primitives and specified in the
output primitive’s structure element. Intrinsic colour data, whcn specified, is conditionally used to determine the intrinsic
colour of an output primitive.
3.31 isoparametric curve: A curve on a parametric surface produced by evaluating the surface over the range of one of
its independent variables while holding ils other independent variable constant.
3.32 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 of the independent variables and is used in computing the B-spline basis polynomials.
3.33 light source: A simulated source of light.
3.34 light source direction: A unit vector that defines the orientation of oriented light sources.
3.35 light source state: A field in the traversal state list that selects which light sources in a workstation light source table
are active.
3.36 lighting: See reflectance calculation.
3.37 normal vector: A unit length vector, typically indicating the orientation of afacet or object.
3.38 parameter range: The parameter space over which a parametric curve or surface is defined.
3.39 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.
3.40 parametric output primitive: Output primitives defined as a mapping from a parameter space to modelling coor-
dinates. Parametric output primitives defined in PHIGS PLUS are non-uniform B-spline curve, non-uniform B-spline
curve with colour, non-uniform B-spline surface and non-uniform B-spline surface with data.
3.41 parameter space: The coordinate system of the independent variable(s) of parametric curves and surfaces. The
parameter space is one-dimensional for curves and two-dimensional for surfaces.
3.42 polyline set with colour: An output primitive consisting of an unconnected set of polylines. The corresponding
that is conditionally used to shade the primitive.
structure element may include colour information
ISO/IEC 9592-4: 1992(E)
3.43 portion: A portion of an area primitive refers to one or morefacets of the primitive that are distinguished as a group
from its other facets by some property such as orientation or position relative to a trimming loop. The term can be applied
to groups of explicitly defined facets as well as the facets conceptually used to approximate a non-uniform B-spline
surface.
3.44 positional light source: A light source that contributes to the reflectance calculation dependent on the orientation
and position of an area being illuminated relative to the light source.
3.45 quadrilateral mesh: An output primitive in which an array of quadrilaterals is specified by a two-dimensional array
of vertices.
3.46 reflectance calculation: The computation of the effect of light sources on the colour of an area primitive’s facets.
3.47 reflectance model: An aspect that selects the rejectance calculation and thereby specifies which lighting effects
are to be displayed.
3.48 reflectance formulae: Formulae that model the light reflected by an area primitive.
3.49 reflectance normal: A vector used in the rejectance calculation and indicating the orientation of a primitive at a
point on the primitive. The vector is conceptually perpendicular to the surface of an object being represented by an area
primitive. It is derived from the vertex normals of the primitive, if specified, or thefacet normal.
3.50 reflectance properties: An aspect of area primitives that indicates how a primitive reflects light.
3.51 rendering colour model: The colour modcl used for performing colour intcrpolation during shading and depth
cueing.
3.52 rendering pipeline: A sequence of operations that performs data mapping, lighting, shading, depth cueing, and
colour mapping of output primitives. Each of these operations is considered a stage in the rendering pipeline.
3.53 rigid-body transformation: A modeling transformation composed of at most translation, rotation, and scaling
transformations, where translation transformations move every point of an object an equal distance in the same direction,
the rotation transformations maintain relative angles, and the scaling transformations apply equal scaling in all coordi-
nate dimensions.
3.54 set of fill area sets with data: An output primitivc in which a number of possibly non-coplanar fill area sets are
defined by indices into a single list of vertex data. The fill area sels are not requircd to form a closed or connected surface.
3.55 shading: The interpolation stage of the rendering pipeline.
3.56 specular colour: A reflectance property indicating the effcct of a primitive on the colour of specular reflections
from that primitive.
3.57 specular exponent: A non-negative numbcr indicating the shinincss of an area. The higher the specular exponent,
the shinier the area. A specular exponent of O indicates a minimum relative degree of shininess.
3.58 specular reflection: An approximation of the uncqual reflection of light in different directions from an areaprim-
itive, dependent on the relationship of the viewer to the primitive and the light source.
3.59 specular reflection coefficient: The fraction of non-ambient light contributing to specular rejection.
3.60 spot light source: A light source that contributes to the reflectance calculation dependent on the orientation and
relative position of the area being illuminatcd. Light from such a source is restricted to a semi-infinite cone of influence
and its intensity may decrease as it deviates from the centreline of this cone. (See concentration exponent and spread
angle.)
3.61 spread angle: An angle that dctermines the shape of the cone of influence of a spot light source. Spread angle is the
angle between the center of the cone of influence and the limit of the cone of influence measured at the position of the
spot light source.
3.62 triangle set: An output primitive in which a number of possibly unrelated triangular facets are defined by indices
into a single list of vertex data.
ISOIIEC 9592-4 1992(E)
3.63 triangle strip: An output primitive comprised of a group of adjacent triangles formed by connecting a list of
vertices such that the second and third vertices of each triangle are used as the first and second vertices of the next
triangle.
3.64 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.
3.65 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.
3.66 vertex colour: A general colour associated with each vertex of some output primitives. This colour is conditionally
used within the rendering pipeline to colour and shade the primitive.
3.67 vertex data: Geomewic, intrinsic colour data, or vertex normal data specified at vertices of certain output prim
...