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Written By David Griffiths


Cover Art
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Loading Screen
Click Here To Enlarge Opening Screen

Opening Screen
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Game Screenshot

Loona Rescue

Save the refugees from their home planet by dropping in a landing pod. David Griffin and the BBC micro take you on a rescue mission.

Life on the father planet became unpleasant - pollution, wars and crime were rife. A selection of upright and intelligent citizens were chosen by the supreme government. Their mission - to set up a colony on a new planet in the outer reaches of the galaxy. The project was successful; life on the colonial planet was peaceful for many generations.

Neighbouring colonies observed their lifestyle and became envious of treasures and riches. The inevitable happened - the neighbours invaded, destroying all and pillaging anything of value. The colony was helpless and so the executive commanders ordered evacuation.

A fleet of motherships was launched with the majority of the population. The problem was with the members of the colony in the least accessible parts of the planet. It was decided that the best way to evacuate these humanoids was to drop small landing pods from the mothership to collect them individually and ferry them up to the evacuation craft.

The task is a difficult one due to orbiting meteors and asteroids just above the atmosphere and the invading forces placed mines in stationary orbits around the planet. Only the best pilots are suitable for this demanding mission. You, as an officer of the rescue services, have been called upon to supervise the rescue of these men.

The program in this article was written for the 32K BBC, and although designed on a 1.2 OS, Basic I machine, should work on all other cassette-based systems except where the Tube is used.

The game is a mixture of machine code and Basic. The machine code is employed to execute the more time-consuming routines of moving the mothership and meteors. These are driven by events - see User Guide - and use direct accessing of the screen memory - which is why the program will not work with second processors - for fast motion of multicolour characters.

For smooth animation, the machine code is called at the start of every television field pulse. This is enabled by *FX 14,4 and disabled by *FX 13,4, the event indirecting through &220 - that is, the memory location of the start of my event handling routine is stored in locations &220 and &221 - see Line 1580 of program 5.

The reason I chose to use events is that the necessary moving characters will do so apparently automatically, leaving the Basic program running at almost normal speed to handle the setting up of the screen and the general working of the game.

Type In Five Programs

To get the final version of the game onto cassette it is necessary to type in five programs.

The first is the header for the game proper. Program 2 contains the data for the graphic characters of the mothership and meteors, and the procedure for storing that data in memory. Care should be taken when typing the data statements. If characters look strange it will probably be due to typing errors in this section.

Program 3 contains the assembler for the machine-code routines. Program 4 holds the definitions of the characters used in the game. Program 5 is the game itself and, due to its length, will be prone to typing errors. It may be helpful to replace line 20 with:

20 ON ERROR MODE 7:REPORT:PRINT "at line";ERL:END

when developing the program, to trap any errors.

The following procedure should be adopted to obtain the program correctly and to store it on cassette.

  1. Type in program 1 and save it on tape by SAVE "LOONA.RESq" (RETURN) (RETURN)
  2. Type in program 2 and RUN it.
  3. Type in program 3 and RUN it.
  4. Type in program 4 and RUN it.
  5. Save the above information with, *SAVE "LOONA.1" 900 D00 (RETURN) (RETURN)
  6. Type in program 5 and save it on tape SAVE "LOONA.2" (RETURN) (RETURN) Although it is not necessary to save programs 2, 3 and 4 on the final cassette, it would be wise to save each program on some other cassette, and then it will be possible to check each of these as well as program 5 for typing errors, if the game does not work.

You will probably have noticed that the character definitions are in one of the temporary programs and the VDU 23 stored in one of the final programs taken care of with the *SAVE in procedure 5 above. I have made use of the fact that the definitions are stored in the computer's memory between locations &C00 and &D00, and so are loaded directly into memory.

For lazy people or those who would rather just play the game than enjoy the frills of title pages, tunes or high score tables, it is possible to type in a shorter version.

Omit lines 20 to 120 from program 1 and the following lines should be left out from program 5:

100 230 to 250
2230 to 2380
2450 to 2480
2500 to 2660
2680 to 2790
2850 to 2940

insert:
230 GOTO 30

For even lazier people the complete program is available for cassette. Send 4, or 3 and a blank cassette and SAE to David Griffin, 31 Apsley Road, Oldbury, Warley, West Midlands B68 0QY. Alternatively, for those lazy people who are lucky or rich enough to own a modem, the game is available on Prestel via the pages of Viewfax 258.