G007 High Resolution Graphics Pack

ZX Computing

Nick Pearce

THE GRAPHICS SOLUTION Nick Pearce looks at a couple of ways to get high resolution graphics on your ZX81. Owners of the ZX Spectrum will already be familiar with the delights of high resolution graphics. However, ZX81 owners (excepting those with the necessary hardware add-ons) have hitherto been denied that facility, although the excellent results sometimes obtained by enterprising programmers belie the limited graphics set available. High Resolution is a piece of software which goes some way towards remedying this deficiency enabling 256 by 192 resolution displays to be constructed. User-defined characters (lower case alphabet, chess pieces, space invaders, etc) and smooth curves are available using this software on your trusty ZX81 and 16K RAM Pack. The cassette contains three programs: the high resolution toolkit itself, and two demonstration programs. Toolkit is held in a REM statement and occupies about 0.75K of RAM. The Hi-res display file is about eight times as large as normal and is held above RAM-top, which must be lowered with the appropriate POKE command before LOADing - easily forgotten as I found to my cost! The displays are generated using eight commands obtained through USR calls. The PRINT command prints in mini-characters; these are the same width (eight pixels) but one eighth the height of normal ZX81 characters and can be any one of 128 dot patterns. (For truly addressable graphics there would need to be 256 dot patterns, but the 128 available should be adequate for most practical purposes.) For Hi-res printing the screen is divided into 32 columns and 192 lines, and the procedure is to POKE the column number, line number and mini-character code into assigned memory locations from which they can be printed onto the screen. The method is a little tedious (it is particularly frustrating trying to find the right dot pattern for the required characters) but the results are worth the effort. Hi-res characters can be moved around the screen and so games featuring high resolution graphics are possible (movement is slow in BASIC, but could obviously be speeded up using machine code). The PLOT command gives access to the complete 256 by 192 pixels. Plotting is obtained in a similar fashion to printing; the column and line coordinates are POKEd, followed by a USR call to plot the screen pixel. An instruction booklet is included with the package. This explains the various Hi-res commands and lists the mini-characters available and their codes - it also gives some examples of how high resolution graphics can be used and incorporated in BASIC programs. I felt the booklet could have been more comprehensive; the inexperienced programmer may find it a little inadequate. I did not find the High Resolution package a particularly easy program to use, relying as it does on POKE commands and USR cells. However, experienced machine code buffs should not have any difficulty using it effectively. Computer Rentals are to be congratulated for producing this high resolution software for the ZX81. Not perfect, but a commendable achievement. High Resolution is priced at £5.95 from Computer Rentals. [redacted]. G007 HIGH RESOLUTION GRAPHICS PACK - NOTTINGDALE TECHNOLOGY CENTR Th G007 Is a very powerful piece of hardware for the ZX81. It provides true high resolution graphics which, together with a comprehensive range of graphics commands, gives features usually found only on quite advanced machines - such as line drawing and textured area filling. The G007 commands are easy to use and have been achieved by extending the functions of some of the normal BASIC statements. Particularly versatile is the new PLOT command which is in the form PLOT n,x,y. The coordinates x and y specify a position on the 256 by 192 Hi-res screen; n is a new parameter which is used to select any one of the 115 separate functions. PLOT ON... To give an idea of the procedure and the facilities available, some examples are: PLOT 34,x,y draws a coarse dotted line from the previous plot position to co-ordinates x,y; PLOT 102,x,y draws a chain dotted line to coordinates x,y relative to the previous plot position; and PLOT 42,x,y fills the triangle between x,y and the two previous plot positions in black. User-defined characters are also easily obtained. The G007 allows the 32 characters of the ZX81 from inverse 4 to inverse Z to be readily re-defined (the old inverse video characters can still be obtained since the Hi-res print mode allows characters to be printed in inverse video). To re-define a character, the eight binary numbers representing each row of eight pixels have to be worked out; these are then POKEd into the appropriate locations in the 'character table' in RAM. The normal low resolution mode of the ZX81 is still available with the G007 in use, and the ZX81 may be freely switched between the two modes without losing the contents of either. The Hi-res display file takes about 6.4K of RAM. The Hi-res display can be copied onto the printer, and programs and displays can be SAVEd on cassette. The unit comes with a comprehensive and very well, written manual which also gives a number of example programs. The G007 itself comes in an attractive black plastic case measuring about 17cm by 3am by 6.5cm and is contoured to fit snugly between the ZX81 and the 16K RAM Pack. POWERFUL This is a very powerful high resolution graphics pack. The commands have been well thought out and it is a pleasure to use. Once you have used it for a few programs you will wonder how you ever managed without it. The problem for the ZX81 owner is considering hardware of this sort is whether to expand or to upgrade to obtain the desired facilities. Those who select the former option should find the G007 an excellent investment. The G007 High Resolution Graphics Pack costs £32 excluding VAT (plus 75 pence P&P) from Notting Dale Technology Centre Ltd. TFL (ZX81), [redacted].

A sample screen illustration using Notting Dale Technology Centre's Graphics Pack.

An example screen dump using the G007 High Resolution Graphics Pack.

The G007 High Resolution Graphics Pack from Notting Dale Technology Centre.

Sinclair User

Stephen Adams

NEW COMPANY GOES HI-RES A high-resolution graphics pack designed to work on a ZX-81 with at least 8K of memory is the G007 produced by the Nottingdale Technology Centre. By extending certain commands in Basic such as SLOW, FAST, CLS and PLOT it gives the ZX-81 a 256 x 192 dot screen - it is slightly bigger but to keep the calculations simple it is limited to that. The extra number at the from of the commands gives access to the extra commands, i.e., CLS 3 inverts the whole screen without clearing it. The routines available allow the plotting of individual pixels on the screen, drawing lines, triangles and parts of circles, as well as shading them. PRINTing may be done to any pixel on the screen as the PRINTing corresponds to the graphics pointer. That enables you to print a character, number or letter at any place on the hi-res screen. The SLOW command determines whether it is printed in black or white and what the background will be. The use of the hi-res screen is enhanced further by the fact that the edit line is constantly on the screen, so INPUT and commands can be given without having to switch backwards and forwards between screens. Both the Sinclair screen and the hi-res version are separate and so clearing one will not elTect the other. Both screens can be SAVEd, LOADed and COI'Yed from Basic. The hi-res screen is stored as the last program line - line G007 - and can be deleted only by a USR routine. The Sinclair Basic will not allow you to SAVE it as a named program, however, so LOAQ'm must be used to get it back. The program is stored in a 2K (2716) EPROM inside the unit and uses the internal memory of the ZX-81 - 1K or 2K - to store its system variables. All of those are described in the manual with the unit, so that the machine code programmer can also use them. There are three example programs, only one of which failed to work. The device goes directly on to the back of the ZX-81, as it has to decode the internal memory into using the 8K-12K section of memory on the ZX-81. That means it could be incompatible with some ZX-81 RAM packs or add-ons. Using it is very easy, as one soon becomes used to adding the extra numbers - they are all fully syntax-checked too - and the display is rock steady. Perhaps the next project for the group will be a colour board, as it would make it a very cheap BBC machine, but using only 6K of memory for the screen. To order the device, send £37.55 to Nottingdale Technology Centre Ltd, TFL (ZX-81), [redacted].