1、BRITISH STANDARD BS ISO/IEC 7942-2:1997 Information technology Computer graphics and image processing Graphical Kernel System (GKS) Part2: NDC Metafile ICS 35.140BSISO/IEC7942-2:1997 This BritishStandard, having been prepared under the directionof the DISC Board, waspublished under the authorityof t
2、he Standards Boardand comes into effect on 15November1997 BSI05-2000 ISBN 0 580 28572 3 National foreword This BritishStandard reproduces verbatim ISO/IEC7942-2:1997 and implements it as the UK national standard. The UK participation in its preparation was entrusted to Technical Committee IST/31, Co
3、mputer graphics and image processing, which has the responsibility to: aid enquirers to understand the text; present to the responsible international/European committee any enquiries on the interpretation, or proposals for change, and keep the UK interests informed; monitor related international and
4、 European developments and promulgate them in the UK. A list of organizations represented on this committee can be obtained on request to its secretary. Cross-references The BritishStandards which implement international or European publications referred to in this document may be found in the BSI S
5、tandards Catalogue under the section entitled “International Standards Correspondence Index”, or by using the “Find” facility of the BSI Standards Electronic Catalogue. A British Standard does not purport to include all the necessary provisions of a contract. Users of British Standards are responsib
6、le for their correct application. Compliance with a British Standard does not of itself confer immunity from legal obligations. Summary of pages This document comprises a front cover, an inside front cover, pagesi andii, theISO/IEC title page, pages ii to vi, pages1 to45 and a back cover. This stand
7、ard has been updated (see copyright date) and may have had amendments incorporated. This will be indicated in the amendment table on the inside front cover. Amendments issued since publication Amd. No. Date CommentsBSISO/IEC7942-2:1997 BSI 05-2000 i Contents Page National foreword Inside front cover
8、 Foreword v Text of ISO/IEC7942-2 1ii blankBSISO/IEC7942-2:1997 ii BSI 05-2000 Contents Page Foreword v Introduction 1 1 Scope 1 2 Normative references 1 3 Definitions 1 4 Concepts 1 4.1 The structure of a GKS-94NDC metafile 1 4.2 Metafile elements 2 4.3 Delimiter elements 2 4.4 Metafile descriptor
9、elements 2 4.4.1 Elements used 2 4.4.2 Functional capability 2 4.4.3 NDC-SET 2 4.5 Control elements 3 4.6 Graphical primitive elements 3 4.7 Attribute elements 4 4.8 Application structure elements 5 4.9 Metafile states 7 5 Abstract specification of new elements 7 5.1 Data type definitions and abbrev
10、iations 7 5.2 Delimiter elements 7 5.3 Metafile descriptor elements 7 5.4 Control elements 7 5.5 Graphical primitive elements 8 5.6 Attribute elements 8 5.7 Metafile defaults 8 6 Mapping from NDC picture to NDC metafile 9 6.1 Introduction 9 6.2 Output primitives 9 6.2.1 SET OF POLYLINE 9 6.2.2 SET O
11、F NURB 9 6.2.3 SET OF CONIC SECTION 9 6.2.4 POLYMARKER 9 6.2.5 SET OF FILL AREA 10 6.2.6 SET OF ELLIPTIC SECTOR 10 6.2.7 SET OF ELLIPTIC SEGMENT 10 6.2.8 SET OF ELLIPTIC DISC 10 6.2.9 SET OF CLOSED NURB 11 6.2.10 TEXT 11 6.2.11 CELL ARRAY 11 6.2.12 DESIGN PRIMITIVE 11 6.2.13 GENERALIZED DRAWING PRIM
12、ITIVE 12 6.3 Output attributes 13 6.3.1 SCISSOR SET 13 6.3.2 TEXT UP VECTOR and TEXT SKEW ANGLE 13 6.3.3 CHARACTER FONT AND PRECISION 13 6.3.4 COLOUR SPECIFIER 13 7 The Character Encoding of the GKS-94NDC Metafile 14 7.1 Notational conventions 14 7.2 Method of encoding opcodes 14BSISO/IEC7942-2:1997
13、 BSI 05-2000 iii Page 7.2.1 Introduction 14 7.2.2 Opcode assignments 14 7.3 Method of encoding parameters 15 7.4 Representation of new elements 15 7.4.1 Introduction 15 7.4.2 Delimiter elements 15 7.4.3 Metafile descriptor elements 15 7.4.4 Control elements 15 7.4.5 Graphical primitive elements 16 7
14、.4.6 Attribute elements 16 7.4.7 Application structure elements 17 8 The Binary Encoding of the GKS-94NDC Metafile 19 8.1 Overall structure 19 8.2 Primitive data forms 19 8.3 Representation of abstract parameter types 19 8.4 Representation of each element 19 8.4.1 Introduction 19 8.4.2 Delimiter ele
15、ments 19 8.4.3 Metafile descriptor elements 19 8.4.4 Control elements 20 8.4.5 Graphical primitive elements 20 8.4.6 Attribute elements 21 8.4.7 Structure attribute elements 21 9 The Clear Text Encoding of the GKS-94NDC Metafile 23 9.1 Notational conventions 23 9.2 Encoding parameter types 23 9.3 Fo
16、rming names 23 9.3.1 Introduction 23 9.3.2 Words deleted 23 9.3.3 Words used unabbreviated 23 9.3.4 Abbreviations 23 9.3.5 The derived names of new elements 24 9.4 Encoding the NDC Metafile elements 24 9.4.1 Introduction 24 9.4.2 Encoding delimiter elements 24 9.4.3 Encoding metafile descriptor elem
17、ents 24 9.4.4 Encoding control elements 24 9.4.5 Encoding graphical primitive elements 24 9.4.6 Encoding attribute elements 25 9.4.7 Encoding of application structure elements 25 Annex A (normative) Formal grammar 28 A.1 Introduction 28 A.2 Notation 28 A.3 Detailed grammar 28 A.3.1 Metafile structur
18、e 28 A.3.2 Metafile descriptor elements 28 A.3.3 Picture descriptor elements 29 A.3.4 Control elements 29BS ISO/IEC7942-2:1997 iv BSI 05-2000 Page A.3.5 Graphical elements 30 A.3.6 Attribute elements 36 A.3.7 Terminal symbols 41 Annex B (normative) New element list 45 B.1 Introduction 45 B.2 Delimit
19、er elements 45 B.3 Metafile descriptor elements 45 B.4 Control elements 45 B.5 Graphical primitive elements 45 B.6 Attribute elements 45 Figure 1 General form of metafile 1 Figure 2 General form of pictures 1 Table 1 Opcodes for metafile elements 14 Descriptors: Data processing, graphic data process
20、ing, image processing, computer software, artificial languages, advanced language, GKS, metafiles.BS ISO/IEC7942-2:1997 BSI 05-2000 v Foreword ISO (the International Organization for Standardization) and IEC (theInternational Electrotechnical Commission) form the specialized system for worldwide sta
21、ndardization. National bodies that are members of ISO or IEC participate in the development of International Standards through technical committees established by the respective organization to deal with particular fields of technical activity. ISO and IEC technical committees collaborate in fields
22、of mutual interest. Other international organizations, governmental and non-governmental, in liaison with ISO and IEC, also take part in the work. In the field of information technology, ISO and IEC have established a joint technical committee, ISO/IEC JTC1. Draft International Standards adopted by
23、the joint technical committee are circulated to national bodies for voting. Publication as an International Standard requires approval by at least75%of the national bodies casting a vote. International Standard ISO/IEC7942-2 was prepared by Joint Technical Committee ISO/IEC JTC1, Information technol
24、ogy, Subcommittee SC24, Computer graphics and image processing. ISO/IEC7942 consists of the following parts, under the general title Information technology Computer graphics and image processing Graphical Kernel System (GKS): Part1: Functional description; Part2: NDC metafile; Part3: Audit trail; Pa
25、rt4: Picture part archive. Annex A and Annex B form an integral part of this part of ISO/IEC7942.vi blankBS ISO/IEC7942-2:1997 BSI 05-2000 1 Introduction The NDC metafile provides a file format and encodings suitable for the storage and retrieval of picture information. The file format consists of a
26、 set of elements that can be used to describe pictures in a way that is compatible between systems of different architectures and devices of differing capabilities and design. This part of ISO/IEC7942 extends the provisions of ISO/IEC8632:1992/Amd.2:1995. 1 Scope This part of ISO/IEC7942 provides a
27、file format and encodings for the storage and retrieval of GKS-94Normalized Device Coordinate (NDC) pictures. It is an extension of the Computer Graphics Metafile, Version4 defined by ISO/IEC8632:1992/Amd.2:1995 (all parts). 2 Normative references The following standards contain provisions which, th
28、rough reference in this text, constitute provisions of this part of ISO/IEC7942. 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 ISO/IEC7942 are encouraged to investigate the possibility of applying
29、 the most recent editions of the standards indicated below. Members of IEC and ISO maintain registers of currently valid International Standards. ISO/IEC7942-1:1994, Information technology Computer graphics and image processing Graphical Kernel System (GKS) Part1: Functional description. ISO/IEC8632
30、:1992/Amd.2:1995, Information technology Computer graphics Metafile for transfer and storage of picture description information (all parts). 3 Definitions For the purposes of this part of ISO/IEC7942, the definitions given in ISO/IEC7942-1 and ISO/IEC8632-1/Amd.2 apply. 4 Concepts 4.1 The structure
31、of a GKS-94NDC metafile The structure of a GKS-94NDC Metafile follows the Computer Graphics Metafile (CGM) standard (ISO/IEC8632-1:1992). It is shown inFigure 1. MF is used as an abbreviation for METAFILE. A Computer Graphics Metafile is a collection of elements from the standardized set. The BEGIN
32、NDC METAFILE element is followed by the METAFILE DESCRIPTOR (MD). After this the pictures follow, each logically independent of each other. Finally the Metafile is ended with an END METAFILE element. Apart from the BEGIN NDC METAFILE, END METAFILE and Metafile Descriptor elements, the metafile is pa
33、rtitioned into pictures. All pictures are mutually independent. A picture consists of a BEGIN PICTURE element, a PICTURE DESCRIPTOR (PD) element, a BEGIN PICTURE BODY element, an arbitrary number of control, graphical and attribute elements and finally an END PICTURE element (seeFigure 2). PIC is us
34、ed as an abbreviation for PICTURE and BEGIN BODY for BEGIN PICTURE BODY. BEGIN NDC MF MD . END MF Figure 1 General form of metafile BEGIN PIC PD BEGIN BODY . END PIC Figure 2 General form of picturesBS ISO/IEC7942-2:1997 2 BSI 05-2000 4.2 Metafile elements Elements in CGM Version4are used for the ma
35、pping of NDC picture to NDC metafile wherever possible. However, some new elements are introduced to provide functionality required by the NDC metafile which cannot be described within CGM Version4. The new CGM elements are marked by daggers () in the tables in this section. The scope of some CGM Ve
36、rsion4elements has been extended. These elements are marked with a double dagger (?). 4.3 Delimiter elements The NDC metafile includes the following delimiter elements: In NDC metafiles, primitives of the same type may be grouped together to form a set of primitives. The primitives to be included in
37、 the set of primitives being defined are delimited by application structure elements as described in6.2. Application structure elements are also used in the representation of the design primitive (see6.2.12) and the SCISSOR SET primitive attribute (see6.3.1). 4.4 Metafile descriptor elements 4.4.1 E
38、lements used The NDC metafile includes the following metafile descriptor elements: The METAFILE ELEMENT LIST lists at least those standardized elements that occur in the metafile. 4.4.2 Functional capability Following the provisions of ISO/IEC8632-1:1992/Amd.2:1995, the contents of the Computer Grap
39、hics Metafile are defined by the METAFILE ELEMENT LIST element. These shall contain a list of the non-mandatory elements that are utilized in the metafile. Several shorthand names for CGM elements are also provided for use with the METAFILE ELEMENT LIST. The NDC metafile set is designated NDC-SET. T
40、hese shorthand names shall not be considered macro names, nor shall they be construed to be levels of conformance. 4.4.3 NDC-SET The NDC-SET includes the elements which can appear in the NDC Metafile. The elements which are not marked by daggers belong to the CGM Version-4set. The value ranges of so
41、me of the parameters of some CGM elements have been extended. These elements are marked by double daggers. The elements included in the NDC-metafile are: BEGIN NDC METAFILE BEGIN PICTURE BODY END METAFILE BEGIN APPLICATION STRUCTURE BEGIN PICTURE BEGIN APPLICATION STRUCTURE BODY END PICTURE END APPL
42、ICATION STRUCTURE METAFILE VERSION METAFILE ELEMENT LIST VDC TYPE MAXIMUM VDC EXTENT MAXIMUM COLOUR INDEXBS ISO/IEC7942-2:1997 BSI 05-2000 3 4.5 Control elements In GKS-94CLIP INDICATOR and CLIP RECTANGLE elements are the parts of the definition of an output primitive attribute, scissor set. The new
43、 control elements SCISSOR IDENTIFIER and SHIELD INDICATOR are used to provide the mapping of the GKS-94SCISSOR SET attribute (see4.7). 4.6 Graphical primitive elements Graphical primitive elements are those elements that describe the visual components of a picture. Their coordinate arguments, if any
44、, are specified in VDC units. The mapping of GKS-94output primitives to CGM elements is shown in the table below. An extension to CGM was needed to provide this mapping. The new CGM elements are marked by asterisks. Each GKS-94output primitive marked by an asterisk (*) is mapped to a set of the corr
45、esponding CGM elements delimited by BEGIN APPLICATION STRUCTURE and END APPLICATION STRUCTURE elements. The DESIGN primitive is more complicated and its mapping to the CGM elements is described in clause6. GKS elements CGM element CLIP INDICATOR CLIP RECTANGLE CLIP INDICATOR CLIP RECTANGLE SCISSOR I
46、DENTIFIER SHIELD INDICATOR BS ISO/IEC7942-2:1997 4 BSI 05-2000 The CELL ARRAY primitive is mapped to a set of elements which define the way in which the colour values used in the following CELL ARRAY element are defined. The CONIC SECTION element specifies a conic section defined by a3 3matrix (whic
47、h specifies the conic) and two points which define the start and end points of the conic section. The last parameter of the conic section definition is a sense flag which indicates whether it is the clockwise or anti-clockwise section that is required when the conic is closed. The ELLIPTIC DISC elem
48、ent is defined by a3 3matrix which defines the ellipse. 4.7 Attribute elements The mapping of GKS-94output primitive attributes to CGM elements is shown in the table below. An extension to ISO/IEC8632-1:1992/Amd.2:1995 was needed to provide this mapping. The new or revised CGM elements are marked by
49、 asterisks. The GKS-94SCISSOR SET attribute is stored in the NDC Metafile using several elements as explained in6.3.1. GKS elements CGM element SET OF POLYLINE* SET OF NURB* SET OF CONIC SECTION* POLYMARKER SET OF FILL AREA* SET OF ELLIPTIC SECTOR* SET OF ELLIPTIC SEGMENT* SET OF ELLIPTIC DISC* SET OF CLOSED NURB* TEXT CELL ARRAY DESIGN GENERALIZED DRAWING PRIMITIVE POLYLINE NON-UNIFORM RATIONAL B-SPLINE CONIC SECTION POLYMARKER POLYGON CONIC SECTION CONIC SECTION ELLIPTIC DISC NON-UNIFORM RATIONAL B-SPLINE TEXT CO
