1、INCITS/ISO/IEC 9636-2-1991 (R1997)(formerly ANSI/ISO/IEC 9636-2-1991 (R1997) for Information Technology -Computer Graphics -Interfacing Techniques forDialogues with Graphical Devices (CGI) -Functional Specification -Part 2: ControlANSI/ISO/IEC 9636-2-l 991 Redesignation of ANSI X3.161 (never publish
2、ed) American National Standard for Information Technology - Computer Graphics - Interfacing Techniques for Dialogues with Graphical Devices (CGI)- Functional Specification - Part 2: Control Secretariat Computer and Business Equipment Manufacturers Association Approved August 6,1992 American National
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9、1 West 42nd Street, New York, New York 10036Copyright 1991 by Information Technology Industry Council (ITI)All rights reserved.These materials are subject to copyright claims of International Standardization Organization (ISO),International Electrotechnical Commission (IEC), American National Standa
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11、 1250 Eye Street NW, Washington, DC20005.Printed in the United States of AmericaContents Page Foreword . Introduction . 1 S-pe 2 Normative references . 3 Concepts . 3.1 Introduction . 3.2 Virtual Device management . 33.1 Device control 3.23 Drawing surface . 3.2.3 Deferral mode . 33.4 Serial synchro
12、nous interface . 33 CoLY*.Y BNI: requires that the Viiual Device complete the display of an image “Before the Next Interaction”, that is, before the next interaction with a Logical Input Device gets underway; If an interaction is already underway (i.e. some LID is initialized for events) then BNI is
13、 equivalent to ASAP, ASAP: requires that the Virtual Device complete the display of an image “As Soon As Possible”. Note that none of these values requires an implementation to delay the display of an image. On the other hand, for hard-copy devices, the CGI does not require a page to be printed per
14、function. Explicit control of deferral is provided by the EXECUTE DEPERRED ACTIONS function which ensures that any pending actions are completed (such as rendering any buffered output so that the operator can see it). The CGI requires that any soliciting function immediately following EXECUTE DEPERR
15、ED ACTIONS will not return data until all pending actions ate performed and the drawing surface is up to date. NOTE-Some implementations, such as buffered one-way output devices, may be unable to support Deferral Mode ASAP. 33.4 Serial synchronous interface The CGI is a serial synchronous interface.
16、 There are no asynchronous signals over the interface to report events (whether from input interactions or from environmental changes) or the occurrence of errors. The CGI is therefore able to guarantee synchronization of its soliciting functions, including DEQUEUE ERROR REPORTS, with preceding func
17、tion executions. Invocation of DEQUEUE ERROR REPORTS will return all errors detected as a result of the execution of the preceding functions provided the error queue has not overflowed. This synchronous interface does not preclude implementations that have many parallel processes within them. Deferr
18、al allows for this potential parallelism within the implementation and the function EXECUTE DEFERRED ACTIONS provides a client with some degree of control of this parallelism. 3.3 Coordinate space concepts 33.1 The Virtual Device coordinate system Coordinate data across the CGI is specified in Virtu
19、al Device Coordinates (VDCs), except where a direct reference is made to the drawing or display surface. VDC space is an abstract space described in more detail below. The subset of VDC space specified by the finite VDC extent is mapped to a portion of the physical device drawing surface specified b
20、y the device viewport. here are two ways for a CGI client to ensure isotropic mapping from VDC space to the display surface: by asking the CGI to enForce it, or by using a VDC extent whose aspect ratio matches the visual aspect ratio of the selected device viewport. Entries in the Output Device Desc
21、ription Table provide the information that enables the client to ensure isotropy without resorting to implicit CGI mechanisms. 4 ISO/IEC 9636-2 : 1991 (E) Coordinate space concepts Concepts Furthermore, the CGI allows viewport specifications to cause the entire image to be mirrored relative to the n
22、ormal orientation, in either axes. The Device Viewport Mirroring entry in the Control Description Table provides information on the support of this mirroring capability. 3.32 Device coordinates The drawing surface and display surface are addressed by means of a Cartesian coordinate system. The Displ
23、ay Surface Bottom-Left Comer and Display Surface Upper-Right comer entries in the Output Device Description Table specify this physical device coordinate system. Although the graphic object pipeline model recognizes an abstract DC space with real coordinates, the only form in which device coordinate
24、s are passed across the CGI is as integers. If the implementation uses raster techniques, then the units of DCs correspond to single pixel displacements. 3.33 Device viewport The - in physical device coordinates, which requires either inquiry or prior knowledge of the device. The device viewport is
25、specified in terms of two points (on the diilay surface) at diagonally opposite corners of the rectangle. The order in which the points are specified is significant. The WC-to-Device Mapping entry in the Control State List may force isotropic mapping. If the current VDC extent, device viewport, and
26、device viewport mapping would not lead to an isotropic mapping, the VDC extent is mapped onto a subset of the specified device viewport. This subset is defined by shrinking either the vertical or horizontal dimension of the current device viewport, as needed, to reach the required aspect ratio. This
27、 smaller effective device viewport is used to define the coordinate mapping from VDC to the devices coordinates. The placement of the effective viewport rectangle within the original one can be specified. This placement can be one of LEFT, RIGHT, or CENTRED when the shrinking is horizontal, and TOP,
28、 BOTTOM or CENTRED when the shrinking is vertical. These meanings are relative to the display surface. (See figure 1.) 3.3.4 VDC space and range Graphics output functions are used to define virtual images. The coordinate data given as parameters to these functions (that is, points in the virtual ima
29、ge) are specified as absolute two-dimensional Virtual Device Coordinates (WCs). VDC space is a two-dimensional Cartesian coordinate space of infinite precision and infinite extent. Only a subset of VDC space, the VDC range, is realizable by the CGI client. The VDC range comprises all coordinates rep
30、resentable in the format specified by the declared VDC type and limited by any applicable precision; thus, the VDC range is not directly set by the client. The VDC range is a finite discrete subset of VDC space (i.e. it does not provide a continuous range of values). VDC space can be addressed with
31、either integer or real coordinate data, determined by the VDC Type entry in the Control State List and controlled by the VDC TYPE function. The granularity and realizable extent of the VDC range is affected by either the VDC INTEGER PRECISION REQUIREMENT function or the VDC REAL PRECISION REQUIREMEN
32、TS function, depending on the VDC Type. The Control Description Table indicates which of integer and real types am supporWl for WCs. Refer to 3.5.1 for further information on precision control. 3.3.5 VDC extent The VDC extent is the portion of VDC space that is to be mapped onto the effective device
33、 viewport on the drawing surface of the Virtual Device. The extent is set by specifying the addresses (in VDC space) of two opposite comers of a rectangular region. Values outside the VDC extent are permitted in CGI functions. 5 ._._ g _I_-. _ - I -_- _. _L_ ._.w_i_ . -. ISO/IEC 9636-2 : 1991 Q Conc
34、epts Coordinate space concepts VDC Extent VDC-to-Device Mapping VDC Extent = (0, 0), (32676.32676) Isotropy = FORCED Horizontal Alignment = LEFT Vettical Alignment = BOTTOM Specification Mode of Current Device Viewport = FRACIION OF DISPLAY SURFACE Metric Scale Factor of Current Device Viewport = 1
35、.O Requested Device Viewport = (0.0.0.0). (1 .O. 1 .O) Effective Device Viewpott = (0.0,O.O). (0X566.1.0) Display Surface Effective Device Viewport Figure 1 - An example VDC-to-Device Mapping. The values of the coordinates for either dimension may be either increasing or decreasing from the first to
36、 the second corner. In this way, the sense of the coordinate system of VDC space relative to the dmwing surface is established (see ligure 2). The transformation which maps VDC points to the drawing surface is called the VDC-to-Device Mapping. The VDC-to-Device Mapping maps the fmt point specifying
37、the VDC extent onto the comer of the effective device viewport corresponding to the fust point specifying the device viewport, and similarly for the second point. The mapping is linear in each dimension, but is not necessarily isotropic (e.g. a circle in VDC may not appear round to the viewer). If t
38、he values of the device viewport mapping entries do not force isotropy, an isotropic transformation can still be assured if the numerical aspect ratio of VDC extent matches ihe physical (not necessarily numerical) aspect ratio of the device viewport. Angular directions are defined as follows: positi
39、ve 90-degrees is defined to be the right angle from the positive x-axis to the positive y-axis (see figure 2). Whether changes to the VDC-to-Device Mapping take place immediately, can be simulated, or lead to an implicit regeneration, is determined by the Dynamic Modification Accepted For VDC-to-Dev
40、ice Mapping entry in the Output Device Description Table. The terminology used in the description of primitives and attributes refers to increasing coordinates from the fast to the second corner relative to the device viewport. If a coordinate system is chosen with decreasing coordinates from the fi
41、rst to the second corner in one of x or y, the rendered objects shall be mirrored. If decreasing in both x and y. the rendered objects shall be rotated by an angle of 1800. 3.3.6 VDC tailoring The ability to specify the VDC range and the VDC extent provides the flexibility to configure the Virtual D
42、evice coordinate space to match various needs. It may be configured as an abstract, normalized coordinate range for maximum device independence. It may also be configured to match the address range and resolution of some target device (e.g. in order to avoid abasing problems or increase performance)
43、. If the Virtual Device coordinate space is configured to match the address range and resolution of a raster device, it may be necessary to know whether or not the pixels lie on or between the coordinates. Where pixels lie relative to the coordinates is indicated by an entry in the Output Device Des
44、cription Table. The preferred behaviour is that coordinates lie between pixels. Coordinate space concepts SecMIdpoint ISO/IEC 9636-2 : 1991 (E) Concepts of Device Viewpoxt c +90 I- I INCREASING X -B-m-B- First point of Device Viewport VDC extent (0.0,O.O). (1.0.0.75) Second point of Device Viewport
45、A i INCREASING I Y I I INCREASING X ImBB-ss-s- b _ First point of Device Viewport VDC extent (0.0,8.5), (11.0.0.0) Figure 2 - VDC extent establishes the reference directions relative to the drawing surface. 7 _ -_-. d- A_ .-.-.D”L-c. . .-u- -c-* .-_-. -,_Lij-k-. *-i-aiLA_l_ ISO/IEC 9636-2 : 1991 (E)
46、 Concepts Coordinate space concepts 33.7 Drawing surface clipping Drawing surface clipping conceptually occurs in abstract DC space before the final physical rendering step. The Drawing Surface Clip Indicator and Drawing Surface Clip Rectangle entries in the Control State List provide control over a
47、ny other non-standard functions shall be called ESCAPE. No other constraint on the functional intent or content of data passed by the ESCAPE mechanism will be imposed. For example, ISO/IEC 9636 does not preclude the data record of an ESCAPE from containing a transformable point list. There are two E
48、scape Functions defined in ISOiIEC 9636: - ESCAPE provides communication of non-standard device-dependent or system-dependent data from the client to the Virtual Device; - GET ESCAPE provides for the implementation of non-standard device-dependent or system-dependent soliciting functions, such as in
49、quiry or retrieval, by providing a return parameter (data record). 3.53 External functions External functions communicate information not directly related to the generation of a graphic image. The MESSAGE function specifies a string of characters used to communicate information to an opemtor. This function can be used to provide special device-dependent information necessary to manage the device. Control over the position and appearance of the character string is not provided. 3.6 Inquiry concepts Inquiry functions, as defined in clause 6, provide the c
