Computer graphics allows the user to communicate with a computer in pictorial, as well as textual, ways. In many cases, there are just facilities for the display of data in pictorial form rather than numeric form, as with graphs, histograms, maps and drawings. In other cases, graphical input is also possible.
The information here in part A of the Guide is really for complete newcomers to computer graphics, since it deals with some characteristics of graphics devices which may be new (in the rest of this chapter), with the types of graphics device supported by RAL (chapter A2) and with the graphics packages provided at RAL (chapter A3). The last chapter in this introductory part is a glossary which defines various terms that are common in computer graphics work (chapter A4).
Computer graphics devices normally have facilities for drawing lines and/or points as well as text - in fact some do not have direct facilities for drawing text. Lines are called lines or vectors; points are more usually called pixels (a squashed form of 'picture element'). If a device can draw proper straight lines, it is often called a vector or calligraphic device. If it can only produce visible output at predefined points, it is called a raster device: the most common example of this in common experience is a standard colour television. On such devices, lines cannot be produced exactly straight because output is limited to the pixel positions.
On all graphics devices in common use, the end points of vectors, the starting point for text and the positions at which pixels can be visible are all constrained to be on a regular, rectangular grid called the raster. On some devices, where there are a small number of lines making up the grid (ie the addressability of the grid is very coarse) this can be a problem when doing precise work such as viewing proofs of a document; in other situations the coarseness may not be a problem. For some plotters (particularly drum plotters) the possible range of values in at least one direction may be very large, but for most devices there are limits in both directions.
Users who are looking at using computer graphics should appreciate that different equipment (and in some cases different software packages) is appropriate for different applications. The addressability of the device is only one criterion; the visible resolution, physical size of the output, speed at which the device can produce different types of output, number of colours or shades of grey and cost of materials all have to be taken into account when choosing the best method.
This chapter deals with the types of graphics device supported on the Rutherford Central Computer system by the graphics systems described in this manual. It does not describe the devices in any great detail, since the full information on them is given in chapter H2; rather it compares the various devices so that users can be aware of the features of each and choose the device that best suits their purpose.
There are three major types of graphics device available to RAL users:
A fourth type of device, the hard-copy unit, does not have a real existence of its own and so is described with the terminals to which it can attach.
There are several different models in this range, including 4006, 4010, 4012 or 4013, 4014 or 4015 and 4016. They all work in the same way and are broadly compatible, although very different in size and resolution.
The basic principle used is that any picture written to the screen is stored, on the screen, until the whole screen is cleared. The displays are vector devices, so straight lines are not broken onto raster lines. The form of screen makes it all but impossible to support any different brightness levels or grey scales; the output is bright green on a dark green background.
As well as vectors, the displays provide high speed text output in a single font; on 4006 and 4010 displays this is upper case only; on the others full ASCII including lower case is provided.
Hardcopy units are available that plug into the display and produce an image by 'reading back' the picture stored on the screen; the image produced is black on white.
Storage tube displays are particularly suitable for work where a large number of vectors are being displayed and when the user is happy for the picture to be built up slowly. Because all interaction from the keyboard is also displayed on the screen and is not scrolled or erasable, it is not so useful for interactive work.
The major distinctions between the models are as follows model is used as the basis:
There is range of Sigma terminals, all of which are raster terminals. Some are black and white systems (S5600, S5671), some are capable of grey scale (S5672/3/4, S5470) and others are colour displays (S5664, S5680). Apart from the S5664, which uses an ordinary text screen for a keyboard and text display and has a separate colour monitor, all the displays are self-contained.
The terminals have a wider range of graphics facilities than Tektronix storage tubes, including multiple characters sizes, facilities for filling areas, more linestyles and definable symbols stored in the terminal. These are available to the user when the terminal is in 'native' mode; in addition all the terminals except the S5600 can be switched to react to Tektronix code.
All the terminals have lower case text for both input and output and have a graphics cursor for input of position information from the terminal.
Hardcopy devices, made by Tektronix, are available to record screen images.
The fact that, in native mode, interaction with the user can use the scrolling text memory means that these terminals are more suitable for applications than storage tubes; the net speed of the terminals in native mode for operations that are also possible on Tektronix terminals is about the same in most cases.
The models are as follows:
Support of these is currently exactly as for Tektronix storage tubes.
These terminals are not supported from the IBM or VAX systems but are supported from the ICF graphics systems. Support from the IBM systems in the future is unlikely because of communications problems.
These terminals are dedicated, high capability colour raster terminals, attached to the Starlink VAX systems for image processing. They are currently supported by GKS 6.2 only.
These are supported by the graphics system on the ICF systems and by GKS 6.2 on the Starlink VAX computers. Support from IBM systems is unlikely because of communications problems.
These are currently supported by GKS 6.2 on the Starlink computers but support from the IBM systems is planned by Summer 1982.
These are supported only by the ICF graphics systems and are only connected to the ICF computers. Usage from the IBM and VAX systems may be possible in the future by transferring files to an ICF computer.
This is currently only supported by GKS 6.2 on the Starlink computers, although connection to other systems via a raster-generator controller is being examined.
This is a very versatile film recorder, capable of working directly to 16mm or 35mm film, black and white or colour, to 105mm microfiche or to 12 inch wide hardcopy paper. It has high speed facilities for text and vectors.
Its addressability is 16384 * 16384 although a slightly reduced section of this area is used on all cameras except microfiche. The resolution on hardcopy paper is around 4 or 5 rasters, or about 1/300 inch. It registers each frame very accurately, allowing successive frames of film to be viewed without any jitter.
Its precision and speed make it useful for all forms of output where quality and resolution are more important than speed of delivery, since all output is subject to delay when being sent to the user. With some additional routines available at RAL, it is suitable for the production of arbitrarily complex documents, as well as large volume outputs.
Further details of its capabilities are given chapter H2.
Rutherford has provided graphics systems of one sort or another since 1967, initially for in-house special users, but now for all users supported on the Rutherford computers. As a result of there having been no standard graphics system (in the same way as Fortran is a standard scientific computer language), a variety of graphics systems have been developed and acquired by the laboratory over the years. In some cases a new system has superceded a previous one; in many cases a new one has just been added to the list of those supported.
Since 1978 there has been a project to rationalize the graphics systems available on at least the Central Computer System. This manual describes the graphics systems that are available on it. Each of the systems described is available on some other system or systems: SMOG is available on the BCRG VAX 11/780; GINO-F is available on all ICF machines and GKS (version 6.2) is available on the Starlink VAX 11/780's.
Since the beginning of 1982 it has been likely that an international standard for computer graphics, called GKS, will be adopted. Staff at RAL have been heavily involved in the development of GKS and RAL is committed to providing GKS on all systems supported by RAL. The initial release of RAL GKS will be in January 1983, on VAX and PERQ; IBM, GEC and Prime systems will follow. This manual has been written at a time when GKS (version 6.2, before standardization) is available on the Starlink VAX systems, but in such a way that GKS can be merged into the manual, as part C, when the system is released.
SMOG was written in 1974/5 at the Atlas Laboratory. It was a simplified version of SPROGS, which had been running on the ICL 1906A for some years. The main aim of SMOG was to provide a simple means of access to the facilities of the FR80, together with preview facilities on terminals and pen plotters.
Since 1975, SMOG has been implemented on the RAL IBM systems and become the most heavily used system there. It still shows traces of its ancestry, but has had facilities added to it to make it useful under CMS when programming directly to user graphics terminals. More recently, it has had routines added to it to access additional facilities for complex text output now available on the FR80 - see chapter D10.
On the IBM systems, a large number of high level routines, for drawing graphs, histograms and maps, for producing contour diagrams and for curve fitting, have been available above SMOG; physically they were held in the same library. These routines are described separately in this Guide - the whole of part D is devoted to them.
SMOG is a reasonably small system, good for 2-D output and graph drawing. It has facilities for driving all the supported features of the FR80 and for controlling graphics devices when online. It has no facilities for manipulating graphics data structures, nor any for producing multiple different views of objects; its 3-D facilities are rudimentary and at present GINO-F should be used for this type of work.
This is a package that is widely available in the UK; it has facilities for defining 2-D and 3-D objects and manipulating them and so is much used for architectural and engineering work.
There is a library of graph-drawing routines (GINO-GRAF) available above GINO-F on the IBM systems; on the ICF systems other GINO packages are also available.
A full description of GINO-F is given in the GINO-F documentation which is not included in this Guide since it would otherwise double the size of the Guide. A brief description and details of how to use GINO-F on RAL systems is given in chapter G1.
This package was written in about 1970 at Rutherford. It has very restricted facilities, only covering things that were possible on a Tektronix 4010 type of device. Originally the MUGWUMP package only provided access to the MUGWUMP filestore, but this is no longer true. Support for the MUGWUMP package is now frozen - users are encouraged to use SMOG or GINO-F at present rather than MUGWUMP.
The MUGWUMP filestore allows users of batch programs under MVT to create picture files in a common graphics dataset and view them from ELECTRIC; this facility will not be provided once ELECTRIC has ceased to be provided. An equivalent system output of picture files to a common filestore - is available under CMS. This system is available to all graphics packages, not just MUGWUMP.
It is worth noting that from Easter 1983 onwards, users will find that the greatest support effort will go into GKS; thus support of new devices may only be provided from GKS and new high level packages will be implemented calling GKS, not SMOG or GINO-F.
GKS provides, within a single integrated package, access to vector and raster systems, has a highly organized and comprehensive range of input devices and allows programs to inquire about - and hence adjust to the actual characteristics of the graphics devices being used.
As it is likely that GKS becomes an international standard, a large body of software, in the form of both packages and complete application programs, is likely to be based on GKS. In addition, terminal manufacturers are likely to provide terminals with facilities that match the requirements of GKS rather than each defining their own 'standards'.
A full list of these and a description of each is given in chapter G3.
