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Written By David Griffin


Cover Art
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Opening Screen
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Game Screenshot

Scrambler

David Griffin's teletext Scrambler has the speed of machine code but is as easy to enter as Basic

A mountainous wasteland in magenta; the surface is littered with mystery bases, fuel dumps, loaded and unloaded missiles. As you race under the radar, your ship must destroy targets to gain points. Keep a watchful eye on your fuel: bombing or shooting fuel dumps will increase your fuel supply. You have to make sure your fuel tank is full before attempting the next sector.

This is the scenario that greets you in the first screen of Scrambler. The screen changes colour from magenta to red, as you enter the cave. The path of your attacking ship is blocked by bouncing fizzers. These evil creatures just bounce up and down whilst emitting a curious sound to help send you insane. Either try to shoot them down, or try to avoid them with some nifty finger work. A full tank of fuel is almost used up in this phase.

After vast fuel consumption in the cave you will be anxious to replenish your supply in this green-coloured rocky terrain. Fuel dumps and mystery bases occupy the ground, whilst fireball comets occupy the air space. The comets are indestructible, so the only way to survive is to dodge them.

The screen turns blue as the deserted city approaches. This sector has all the hazards of the first one, with the enemy missiles in deep silos. The silhouette of the city at nightfall provides the background for all the action, the missiles coming fast and furious.

The fifth screen consists of large caverns joined by narrow passages being blocked by fuel dumps. Clever use of the boosters and retro rockets is the only way to survive this terrain.

A final colour change from yellow to cyan signals the start of the final sector, the Base. Flying over the futuristic skyline will bring you to the nerve centre of the enemy planet. A well-timed bomb on this headquarters will alter the military situation in favour of the human race.

When the sixth screen has been completed a bonus of 2,000 will be added to your score, and you are returned to the start for an even faster game.

I have written this game in Mode 7 - teletext - for several reasons, firstly it is easier to write routines for right to left scrolling in this mode, there is more memory to work with than when using a high-resolution display and accessing the screen in machine code can be achieved with more speed and less difficulty than is the case with other modes.

The game is written using only one colour for each screen. To cbange the colour in teletext mode a control character is necessary. This would involve an extra gap before and after each part of the display requiring a different shade. This would mean added bulk to the already chunky display.

To get Scrambler into your machine you must do the following: type in listing 1, Save this using:

SAVE "SCRAMBLER"

Type in listing 2, Save using

SAVE"SCRAMB"

To play the game CHAIN in the first program, and allow this one to Load and start the game itself.

Listing 1 is the initialising program. It contains all the necessary assembler, and it creates the data for the reproduction of the terrain. I have stored the information to draw the ground of the planet out of the way in memory so that the game can use the same planet each time the game is played. This also speeds up the game because the routines to print the relief do not have to mess around with random numbers and complex cbecking routines.

Listing 2 is the game and is loaded by the header program described above. The listings are long and will take plenty of time and energy to type in. If you feel you do not have either the stamina or patience for such an epic, I will supply the game on cassette. Send 3 to David Griffin, 31 Apsley Road, Oldbury, Warley, West Midlands B68 0QY.