Supply Blaster is an arcade-type game
for 1 or 2 players. It is written in BASIC and uses redefined
characters in Graphics 17 with a machine code transfer of half a
character set from ROM to RAM and machine code Display List Interrupts
(D.L.I's) which, among other things, splits the background into dark
blue cloud level, lighter blue open sky and ground.
Initially there are choices of the
number of players and of the limit of supplies which must be prevented
from landing and remaining intact on the ground. A player's game ends
either when he has lost all his ships or when the preselected number
of supplies is on the ground.
A player starts with three ships and
the number of ships left at any given time, including the one
currently in play, is shown at the top middle of the screen. Player
1's score is indicated at the top left and, if playing, Player 2's
score at the top right. A high-score stands at the bottom left and the
number of supplies landed and still intact is at the bottom right.
A new ship is set up on the ground to
the extreme left and the object of the game is to score as many points
as possible by moving the ship, with a joystick, in any horizontal or
vertical direction and preventing supplies, which drop from random
points at cloud level, from landing on the ground and building up to
the preselected number. This is done by positioning the ship under a
descending box and firing up at it by pressing the joystick button.
The Player's score is increased for each supply box hit with the
number of points increasing proportionately to both the height of the
box when hit and the height of the Player's ship.
A fuel line is built in just below
ground level and this runs out by a 20th each time a shot is fired.
When the last shot has been used an alarm sounds and a flashing arrow
at the extreme left of the fuel line indicates that the Player must
return his ship to the starting point in order to re-arm and be able
to carry on with the battle. This operation needs to be performed as
rapidly as possible because supplies are still falling and, if the
Players ship is not available and armed, they will of course land!
Just to make life a little more
difficult, random enemy missiles appear from either side of the screen
above certain scores, vertically level with the Player's ship. These
will automatically readjust their aim to any change in the Player's
vertical position and the only way to avoid being hit and destroyed is
to move down behind one or more landed supply boxes so that the
missile impacts with one of those instead. It will be seen that it is
not a bad idea to let a few boxes land, especially near the edges of
the screen.
A second obstacle presents itself,
depending on the supplies limit selected, when an occasional enemy
ship appears from either side of the screen at varying heights. These
chase across the screen towards the horizontal position of a Player's
ship, and if the Player does not shoot quickly enough, they will fire
a laser beam which will destroy the Player's ship. As the game
progresses, these become more difficult to hit as they first begin to
dodge the Player's line of fire and then later combine this strategy
with that of coming down the screen towards him.
Thirdly, after the loss of a ship and
providing a Player has passed a certain score depending on the level
of play, the cloud level drops, thereby making it more difficult to
cover the width of the screen to hit supply boxes which drop from a
lower position.
Just to be fair, guided missiles and
enemy ships will not be launched whilst the player's ship is in the
left-hand column of the screen, which obviously includes the re-arming
process, but remember, it is no good staying there for too long
because further supplies cannot be prevented from landing in the main
play area. A missile will, however, continue on its way if already
launched from the right hand side of the screen. An enemy ship, if
already on screen, will still align itself above the Player's ship and
fire at him, unless he has commenced re-arming, in which case it will
hover until he is re-armed, then it is matter of who can fire first!
The preselected last supply box trying
to land is indicated by a different colour and warning sound as it
descends.
If you fancy your chances of going up
the screen to meet or even pass an enemy ship, just try it!
SCORING:
Points
are scored for shooting a supply box.
A players score is also increased by 250 points for each enemy ship
destroyed. An extra ship is credited at a score of 10,000 points or
more.
Ships can be lost by
Being
hit by descending supplies
Being hit by enemy missiles
Being shot or hit by enemy ships
VARIABLES
| L( |
positions of each
Player's intact landed supplies. |
| S( |
Player(s) score(s). |
| D( |
number of each
Player's supplies down on the ground. |
| X( |
checks for extra
ships. |
| G( |
number of each
Player's ships left. |
| CL( |
Each player's current
cloud level. |
| N |
Number of players. |
| X |
Horizontal position of
player's ship. |
| Y |
Vertical position of
player's ship. |
| X1 |
difference in player's
ship's horizontal movement. |
| Y1 |
difference in player's
ship's vertical movement. |
| E |
fuel level. |
| R |
re-fuelling
(re-arming) level. |
| EO |
selection of enemy
object type. |
| T |
type of enemy object
subroutine line. |
| H |
high score. |
| P |
Player (0 for Player
1, 1 for Player 2). |
| S |
joystick. |
| J |
random selection of
enemy hor. position. |
| K |
random selection of
enemy vert. position. |
| B |
colour of enemy supply
box or initial colour of enemy ship. |
| BO |
normal supply box
character/colour. |
| F |
character/colour of
Player's ship shot |
| DI |
difference in hor.
direction of enemy missile/ship. |
| M |
character/colour of
enemy missile. |
| W |
waiting factor before
enemy ship fires |
| Z |
character/colour of
enemy ship's laser beam. |
| A |
factor to synchronise
refuelling alarm or sound of refuelling operation with explosion
of landed supplies if supplies hit by an incoming missile at the
same time. |
| S4 |
Setcolor 4 memory
location 712. |
| NC |
normal colour of sky. |
| VO |
Voice 0
distortion/volume memory location. |
| V1 |
Voice 1
distortion/volume memory location. |
| V2 |
Voice 2
distortion/volume memory location. |
| V3 |
Voice 3
distortion/volume memory location. |
| FL |
extreme left fuel line
memory location. |
| SK |
DLI machine code
location for sky colour. |
| SL |
Supplies limit
selected. |
| SP |
top left screen memory
location. |
| SC |
Antic enable/disable
location 559 |
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