SPACE FIGHTER version II¢------------------------¢¢Written by John Foskett¢¢Written in Turbo Basic for Compiling¢¢¢¢ --------------------------------------¢ AN ALIEN RACE IS INVADING PLANET EARTH¢ YOU CAN AND YOU MUST STOP THEM¢ --------------------------------------¢¢THE ALIENS OBJECTIVE¢¢The aliens objective is simple, to take over the Earth and to destroy all life forms.¢¢THE ALIEN FLEET¢¢The evil alien fleet comprises of several different types of space craft, all based upon their highly successful circular design. The design that gave birth to the rumours of flying saucers. The alien space craft are of the latest design and are extremely fast, highly manouverable and have the capability to hyperwarp. The aliens have also a means of bypassing the visible light spectrum enabling their space vehicles to have the advantage of invisibility. Each of their space craft is fitted with their deadly accurate, high powered laser. It is the only weapon they have and the only weapon they need. The most feared weapon in the universe.¢¢YOUR MISSION¢¢Your mission is simple, to defend planet Earth and destroy the evil alien fleet.¢ You have been sent into space to board a space stations defence cockpit from where you must defend the Earth. In the cockpit, you have been provided with many first class, hi-tech weapon and defence systems which you must use to defend the Earth.¢*¢YOUR DISPLAY SYSTEMS¢--------------------¢¢THE DISPLAY PANEL¢¢The main display panel below your viewing window is designed as a head up display which superimposes data into the field of view. Therefore the panel appears transparent such that a target may be shot at through the panel. The display panel gives all the necessary information regarding the main weapons and defence systems.¢¢THE ANALYSIS DISPLAY¢¢The analysis display is located at the top of your viewing window again as a head up display. ¢*¢YOUR WEAPONS AND DEFENCE SYSTEMS¢--------------------------------¢¢THE LASER CANNON <LAS>¢¢(use joystick inserted into port 1)¢¢The laser cannon is controlled by using a joystick and is fired using the trigger in the normal way. The laser cannon may also be fired by using the "autofire" system. The joystick is used to control the position of the aiming cursor which must be positioned on top of a target to achieve a strike. As an aid to its location, the aiming cursor continually switches between green and purple. The laser cannon uses 25 energy units for each shot, whether or not a target is hit. A target will not always be destroyed when hit by the laser, it may be damaged, neutralised or may even self destruct.¢ Any CONSOLE key may be pressed in conjunction with the joystick to give rapid (x2) cursor movement.¢ The ARROW keys are used to provide instant movement of the cursor to any of its extremities. To achieve this the cursor must reside in the opposite half of the screen and the joystick must be central.¢ The "H" key is used to "home" the cursor to its initial starting position between its indicating marks. This can only be achieved if the cursor resides anywhere outside the paralysing corner marks and the joystick is central.¢ All instant cursor movement uses 10 energy units.¢¢THE WANDERING FORCE FIELD MINES <MIN>¢¢The wandering force field mine is a highly explosive device launched into space to trap unsuspecting alien space craft. Only one mine can be used at a time which is launched by using the "M" key. Once a mine is launched, it is indicated on the display panel using the "<" marker and will remain in space wandering around until it is struck by a target. Launching a mine requires 20 energy units. The wandering force field mine looks like faint glistening cloud moving in space.¢¢THE HOMING TORPEDOS <TOR>¢¢Homing torpedos are radar guided explosive devices which are programmed to seek out a target, lock onto it and destroy it. A torpedo is launched by pressing the "T" key and can be seen to emerge from below the display panel, travelling out into space on its way to its target. Only one homing torpedo can be used at a time, which is indicated on the display panel using "<" mark as before. Launching a torpedo uses 500 energy units. If a target is destroyed by another means, such as by striking a mine then the torpedo will seek out the next target and destroy that. Thus a torpedo always guarantees a strike and is never wasted.¢ A homing torpedo can even seek out an invisible target by following its radar image, although it must wait for it to reappear before destroying it.¢¢THE PARALYSER <PAR>¢¢This is a device that must be used in conjuction with another weapon since it cannot destroy a target itself. The paralyser is a very effective way of jamming the targets control systems to make it an easier target to strike with the laser cannon. The paralyser uses 300 energy units every time it is used against a target and once activated the target will remain out of control until it is destroyed. The paralyser can only be operated against a target within the field indicated by the corner marks and provided that it is within range. The paralyser is operated by the "P" key and is indicated by the "<" mark on the display panel as before.¢¢THE FORCE FIELD SHIELDS <SHI>¢¢The force field shields are used for protection against the aliens fire power. They may be switched on or off at any time by pressing the "S" key. When used, the shields are continually consuming energy, so they must be used with care. Space takes on a reddish hue when the shields are used. Operation of the shields is indicated on the display panel using the "<" mark as before as well as display panel data showing in red. The shields automatically turn off in the event of insufficient levels of energy. Using the shields does not give complete protection against alien fire power, but greatly reduces the chances of a hit. You can of course use all of your own weaponry through the shields.¢¢AUTOFIRE <AUT>¢¢The autofire facility is designed for use in conjuction with the laser cannon. It enables full concentration to be used "chasing" a target without having to worry about firing the laser. The autofire facility is operated by pressing the "A" key and uses 25 energy units each time. Once operated, it is indicated on the display panel using the "<" mark as before and will remain active until a strike is achieved with the laser cannon. Using autofire, the laser is fired by cursor contact with a target and naturally a strike will only be achieved if the cursor remains "on target" in the usual way.¢¢COMMUNICATIONS <COM>¢¢All messages from your on-board computers is displayed on a single line within the display panel. This facility keeps you informed at all times. At any time the "C" key may be pressed to show again the last message displayed at the cost of two energy units for each time. Should the communications system become damaged by a hit from alien fire, then garbage or a blank display may result.¢¢THE GRID X/Y METER¢¢This meter provides a digital read out of a targets position in space by the use of co-ordinates. Your view into space is divided into ten sectors in both the X and Y axes, the sectors are labelled from "0 to 9", where X=0 is extreme left and Y=0 is extreme top.¢¢THE RADAR SCANNER¢¢The radar scanner allows a target to be tracked at all times even when it is out of view or when invisible. The position of the radar scanners "blip" represents a targets position in your field of view.¢¢THE ALTIMETER AND RANGE METER¢¢This is a dual purpose instrument to the right of the radar scanner which contains two markers. The red marker is the altimeter and the blue marker, the range meter. ¢ The altimeter tracks a target in the vertical plane only, its marker can be seen to follow the radar scanners Y axis.¢ The range meter displays a targets distance in space, where the top of the scale is the most distant.¢¢ENERGY LEVEL <EN>¢¢This records the total amount of energy remaining.¢¢HITS <HIT>¢¢This records the total number of strikes or hits achieved.¢¢HITS RECEIVED <REC>¢¢This is the total number of hits received from alien fire power.¢¢ELAPSED TIME <SEC>¢¢This is the time in seconds that has elapsed between the time of your last hit and the time of your previous hit.¢¢TARGET ANALYSIS¢¢Your on-board computers have been pre-programmed to analyse all possible targets and to display all information instantly in three catagories which are as follows....¢¢1. CLASSIFICATION <CL>¢¢The classification of alien space attack vehicles is dependent upon its design and a letter of the alphabet is alocated to each type.¢¢2. RATE OF FIRE <RT>¢¢This is the rate of fire of alien space attack vehicles. It is based upon a scale of "0 to 9" where 9 is the highest rate of fire.¢¢3. ACCURACY OF FIRE <AC>¢¢This is the accuracy of fire of alien space attack vehicles. Again it is based upon a scale of "0 to 9" where 9 is the most accurate.¢*¢PROGRAMMING DETAILS¢-------------------¢¢THE SCREEN¢¢The screen used is mode 15 without a text window (mode 31). All text being printed using Turbo's "TEXT" command.¢¢PLAYER MISSILE GRAPHICS¢¢All four players are used in the program, together with two missiles combined to form a fifth player, they are as follows....¢¢Player 0 -- Laser cannon cursor¢Player 1 -- Alien space craft¢Player 2 -- Wandering force field mine¢Player 3 -- Homing torpedo¢Missile 0 - Radar scanner marker¢Missile 1 - Altimeter marker¢¢The player and missile shapes are stored in strings and moved into the respective player/missile stripes via Turbo's "MOVE" command thus....¢¢MOVE ADR(X$),PMBASE+1024,LEN(X$)¢¢(where 1024 is player 0 and X$ is the string concerned)¢¢INTERRUPTS¢¢A VBI routine is used to control the colour pulsation of the alien space craft, the laser cannon cursor, the homing torpedos and the glistening of the wandering force field mine. It also disables the attract mode.¢ A small DLI routine is used which alters two colour registers to provide extra colours on screen for the display panel area.¢ Both interrupt routines are stored in page six with the DLI following the VBI.¢¢COMPILER PROBLEMS¢¢When executing the initialising routine at the end of the listing using either EXEC <LABEL> or GOSUB xxxx, the compiled program seems to "lose sight" of the return address from the stack when encountering ENDPROC or RETURN. To get over this problem, two GO# <LABEL> commands are used instead.¢ Only integers can be used in the SOUND commands of a compiled program, unlike BASIC. Hence the use of INT(X) in the two explosion routines.¢ Although the compiler will compile the SOUND statement, it results in an error when run. A FOR-NEXT loop is used instead to turn all sounds off.¢*¢ED: The Compiled version of 'Space Fighter II' appears in this issue of TGR. If you wish to receive a copy of the Turbo BASIC file then send me a disk and a SAE.¢
