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Chapter 9 PAGE 1 STARTREK THE COMPUTER PROGRAM
CHAPTER 9
9.1 Shootback
Now that the Enterprise has been armed with offensive
weapons (Phasers and Photon Torpedoes), and has been provided
with shields, it is time to provide the enemy with a means to
protect and defend themselves. The Klingons are thus allowed to
take hostile action against the Enterprise and are also allowed
to move around inside the quadrant. The flowchart for the
SHOOTBACK subroutine which perform the hostile actions is shown
in figure 9.1 . It is invoked by the main loop if there are any
Klingons in the quadrant, or when the Enterprise moves in a
quadrant containing Klingons. The operation can take place in
any quadrant at any time, so the first thing to test is if the
Enterprise is docked at a Starbase. If it is, the Starbases's
shields protect the Enterprise so there is no need for any
further action in the subroutine. A loop then takes place in
which all eight elements in the Klingon Array are tested. If any
Klingon is active, namely it has a positive amount of energy, and
the "game over flag" is not set, signifying that the Enterprise
has been wiped out by previous Klingon action, then it may take
hostile action. If it does, it can either fire a photon torpedo
or use its phasers.
If it fires off a torpedo, the torpedo can either hit or
miss the Enterprise. if it hits the Enterprise, the sub-system
closest to the point of impact is damaged, if it misses, a
message to that effect is displayed.
If the Klingon has fired a phaser burst, the amount of
energy fired must be computed and deducted from the energy of the
enemy ship. The amount of energy impacting the shields of the
Enterprise must then be determined and subtracted from the amount
of energy that were in the shields. A test must then be
performed to determine if the Enterprise's shields have been
beaten down to zero. If they have, the game is over, the player
has lost so the game over flag is set signifying that event and
the loop is terminated because there is no point in letting the
remaining Klingons in the quadrant fire at a non existent ship.
If the Enterprise is still alive after the hit, the size of the
hit must be examined to see if it was massive enough to
momentarily overload the shields. If such an overload took
place, then one of the ship's sub-systems closest to the point of
impact is damaged.
Each Klingon gets a turn to take hostile action and may or
may not do so depending on how favorable a position it is on at
any time. Once all of them have had their chance, the computer
checks to see if the energy in the shields of the Enterprise is
low, and if it is, displays a message warning the player of that
fact, before the subroutine terminates.
A BASIC language version of the SHOOTBACK function is shown
in figure 9.2. It begins in line 600 with the usual REMark.
Copyright (c) Joe Kasser 1989
Chapter 9 PAGE 2 STARTREK THE COMPUTER PROGRAM
Line 610 examines the state of the condition flag 'C$' to see if
the Enterprise is docked. If it is, the program line counter is
advanced to line 680 bypassing the remainder of the subroutine.
The loop begins at line 620 using the 'FOR/NEXT' technique.
The amount of energy available to the Klingon stored in the K3(I)
array for each possible Klingon is tested. If it is equal to or
less than zero, the inside of the loop is bypassed and the
program counter advanced on to line 670. Also, there is a random
probability that the Klingon, even if it is active will not fire.
In that event, the program counter is also advanced to line 670
bypassing the rest of the loop. The function 'RND(Z)<.1*(I+Z)'
is used to determine the probability of the Klingon taking
hostile action. A random number is generated by the computer.
It is then compared with a number that increases for every
iteration of the loop as follows. The loop counter (I) ranges
from 0 to 7. Each time around, a constant value of one
represented by the parameter 'Z' is added to the loop counter and
the result is multiplied by 0.1. Each time the loop counter is
incremented, the probability that the Klingon will take hostile
action is reduced. For example, the limits are as follows
I PROBABILITY
0 0.1
1 0.2
2 0.3
3 0.4
4 0.5
5 0.6
6 0.7
7 0.8
thus the probability that the first Klingon will not fire is
10%, that the second in the quadrant will not fire is 20% etc.
This technique minimizes the probability that all the Klingons in
the quadrant will fire at the Enterprise so that the player
stands some chance when going into a quadrant containing seven
Klingons. It is "realistic" to expect that not all Klingons will
be in a position to fire at any one time.
The decision as to whether the Klingon fires a torpedo or
its phasers at the Enterprise is taken at the start of line 630.
A random number is generated and compared with the amount of
energy that the Klingon has, divided by five hundred. This
ensures that as the energy level of the Klingon gets lower the
probability of the Klingon Captain deciding to use photon
torpedoes increases and the probability of the Klingon using its
phasers decreases. This is logical because phaser bursts are
ineffectual at very low energy levels. Two "fallouts" from
using the 'IF RND(Z)>K3(I)/500 ' statement are that the Klingon
will never use its torpedoes when it has more than five hundred
units of energy, and, when you are trying to get it to surrender
by beating its shields down to zero slowly, it is liable to keep
firing torpedoes at you. These torpedoes however home in on the
Copyright (c) Joe Kasser 1989
Chapter 9 PAGE 3 STARTREK THE COMPUTER PROGRAM
energy in your shields, so that if you remember to keep your
shields at a minimum level, you should be able to dodge the enemy
torpedoes. If a torpedo is fired, the program flow continues
along line 630 and displays a message stating that a torpedo has
been detected. The program now has to determine if the torpedo
hit and if so, if any damage was caused. 'H' is thus used as a
temporary variable. It is first set to a random percentage of
the amount of energy in the shields of the Enterprise by the
statement 'H=RND(Z)*E1'. Since both the phaser and torpedo hit
sections of the subroutine use the same nested subroutine
starting at line 130 to process the hit and determine if any
damage occurred to the Enterprise, and this subroutine subtracts
the amount of the hit from the energy levels of the Enterprise,
that operation in line 140 must be compensated by adding the
amount of the hit to the energy levels before the nested
subroutine subtracts it so that the net result of the hit will
not effect the energy levels aboard the ship.
Line 630 then advances the program counter to line 660. The
phaser burst is processed in line 640. A random percentage of up
to forty percent of the energy aboard each Klingon is taken from
the Klingon by the statements
'H=K3(I)*.4*RND(Z) : K3(I)=K3(I)-H'
and then the amount of that energy that actually hits the
Enterprise is determined as a function of the distance between
the Klingon and the Enterprise by the statement 'H=H/(SQR((K1(I)-
S1)^2+(K2(I)-S2)^2))^.4' which utilizes basic geometry to
determine the distance based on the row and column co-ordinates
(remember, the square of the sum of the sides of a right triangle
is equal to .....). Line 650 then displays the amount of the
phaser hit, and both the phaser and torpedo hit routines come
together at line 660 which tells the player where the offensive
was launched from. Line 660 displays the point of origin message
even if the short range sensors are damaged, if you wanted to
inhibit that you'd have to modify the line to read
660 IF D(1)=0 THEN PRINT " from sector";K1(I)+Z;",";K2(I)+Z
665 GOSUB 130 : IF F9>0 THEN 680
and introduce a new line (665). Once the message has been
displayed the subroutine beginning at line 130 is called. This
subroutine processes the hit by subtracting the amount of the hit
from the shields of the Enterprise and determining if it was a
massive hit. If it was, then something aboard the ship is
damaged. After returning from the subroutine, the state of the
"end of game flag" (F9) is tested to determine if the Enterprise
was destroyed by the enemy. If it was, the program counter is
advanced forward to line 680 effectively terminating the
subroutine. This is an abnormal exit from the loop, but what is
the point of staying in the loop if the game is over. The
display generated by successive Klingons will be nonsense.
The loop terminates at line 670 when all the enemy ships
have had a turn to fire. The last statement on the line, checks
the state of the shields. If they contain less than one hundred
Copyright (c) Joe Kasser 1989
Chapter 9 PAGE 4 STARTREK THE COMPUTER PROGRAM
units of energy , the computer will display a warning message to
the player. The message contains the 'CHR$(7)' statement to also
provide an audible warning. Line 680 terminate the subroutine
with the usual 'RETURN' statement.
The flow of the SHOOTBACK subroutine may be easier to
understand if it was written in the form shown in figure 9.3 in a
cross between "flowchart" and BASIC.
The second part of the Klingon's defense capability is the
ability to move around. Many versions of the game do not feature
movement by the Klingons. The player thus plays against "sitting
ducks" which makes the game very easy. On the other hand
allowing the Klingons to move in between quadrants complicates
the programming because separate matrices or arrays would have to
be used to store both the actual contents of a quadrant at any
time, and the value the computer placed in it at the time that
the quadrant was scanned. If a Klingon moves out of one quadrant
into another, the arrays will then contain different values. You
may be interested in modifying the game later to add that
capability, letting the enemy slowly move towards the Enterprise
or towards the Starbases, or just move them at random, for they
too can travel at warp speed. That would certainly complicate
the game, because then the map records would not be of any use in
remembering where the Klingons are, but only serve to remember
where the bases are and which quadrants contain large numbers of
stars.
There are a number of algorithms that can be used for moving
Klingons around the quadrant. for example, they can be positioned
at random. They can be moved plus or minus a number of sectors
from their previous position. They can be moved towards the
Enterprise so that they seem to be slowly "coming in for the
kill".
Each algorithm requires a different implementation. The
simplest one to use is that shown in figure 9.4 which moves the
Klingons about at random. It can be argued that since they are
traveling at high speed, maneuvering both to attack and to avoid
the weapons fired by the Enterprise, their movement could appear
to be random.
The flowchart is basically one big loop. The state of each
possible enemy ship in the quadrant is tested. If it is found to
be alive, a random sector is chosen. If that sector is blank,
the Klingon is moved into it. If the sector is occupied by
anything, the Klingon stays where it is. An alternative approach
could be to try again for a blank sector, but why bother. The
sector it is occupying could just as easily show up as the chosen
random sector. This approach does have one side effect. The
more things that there are in the quadrant, the greater the
probability that the sector selected at random will be occupied
and thus the greater the probability that the Klingon will not
move. Each approach used in implementing most functions of the
game may also show up side effects that were not specified.
Copyright (c) Joe Kasser 1989
Chapter 9 PAGE 5 STARTREK THE COMPUTER PROGRAM
Sometimes these side effects work in your favor, sometimes they
don't matter and sometimes an alternative approach has to be
chosen because the side effects are detrimental to the program.
In our case, there can only be up to seven stars, up to seven
Klingons, one starbase and the Enterprise in any particular
quadrant. That means that out of sixty four sectors in the
quadrant, only sixteen can be occupied in the worst case. Nobody
should ever notice that there is a bias towards not moving the
Klingons as a function of the number of objects in a sector.
The BASIC language version of the flowchart could take the
form shown in figure 9.5 which starts at line 700 with the usual
REMark. The loop begins at line 710. The loop used takes the
form of a FOR/NEXT statement.
K3(I) is the flag that contains the state of the Klingon.
If the value stored in the element of the array associated with a
particular Klingon is positive, the Klingon is alive and well.
The test is performed using the statement 'IF K3(I)<=0 THEN 740'.
which causes the remainder of the subroutine to be bypassed if
the contents of the element are equal to or are less than zero.
In other words, if the Klingon is not active.
Line 720 calls the subroutine in line 50 to find a pair of
random numbers between 0 and 7. The last part of the line tests
a sector defined by those co-ordinates to see if it is blank. If
it is not blank, the program counter is advanced forward to line
740 bypassing the remainder of the subroutine.
Line 730 moves the Klingon. The contents of the sector
matrix represented by S(I,J) are set to one, effectively
emptying the sector by the statement 'S(K1(I),K2(I)) = Z'.
Remember, K1(I) and K2(I) represent the position of the Klingon
in the quadrant. The new position is set up by the pair of
statements 'K1(I) = X : K2(I) = Y' and lastly, the contents of
the sector array associated with the Klingon are set to show the
presence of the Klingon by the statement 'S(X,Y) = 4'. The loop
terminates in line 740 as does the subroutine once the loop is
over.
In this version of the game, the Klingons are moved before
they shoot back at the Enterprise. The MOVEKLINGON subroutine is
called before the SHOOTBACK subroutine allowing the Klingon to
shoot after it moved., The hit routine which displays the co-
ordinates occupied by the enemy ship when It fired on the
Enterprise is then up to date when is your turn to shoot. If the
Klingons shot first and then moved, you would not be able to
locate them by the 'hit' message but would have to request a full
short range sensor display each time you wanted to fire.
9.3 Resign
Now that the Klingons can fight back, you ought to be given
the option of resigning from the game. This way, when you are
playing it in its current configuration you can give up and start
Copyright (c) Joe Kasser 1989
Chapter 9 PAGE 6 STARTREK THE COMPUTER PROGRAM
again if you get too badly damaged.
A flowchart of a typical resign sequence is shown in figure
9.6. The flowchart begins by testing to see if any Klingons are
present in the quadrant. An attempt to resign in a battle
situation is teated as an attempt to surrender by the game
simulator. Since Klingons do not take prisoners, your surrender
is not accepted and they continue to try to destroy the
Enterprise.
If the simulator allows the player to resign, a verification
must be performed to make sure that the player realy intends to
resign and did not call the function by mistake. It is good
practice to always verify any critical operation in any program.
In this case, what could be more critical than ending the game.
If the player really did intend to resign, the 'end of game' flag
is set accordingly, if not the flowchart terminates.
9.4 Transporter and Shuttlecraft
The Transporter and the Shuttle allow you to possible obtain
energy and spare parts/materials without docking at a starbase.
You can use the computer to scan the quadrant you are in and
possibly locate sources of energy and materials or parts. You
cannot however stock up on parts to expedite future repairs, you
can only obtain parts to repair anything damaged at the time.
The Enterprise is a starship not a freighter. Should you mine a
lot of energy, and have an excess when you dock at a starbase,
the base will relieve you of the excess and send you on your way
with the standard amount.
The Transporter allows you to beam a landing party down to a
star system. The Shuttlecraft allows you to send a landing party
to the sustem. The transporter uses energy, the shuttlecraft
uses time. Once the landing party have reached their
destination, Mr Spok will notify you how much time the landing
party have to spend on the ground to achieve their aims.
The function of the landing party depends on where they are.
If they have been landed near a source of Dilithium crystals,
they will mine the cystals and then purify them using some
equipment that Mr Scott will lash together. Mr Spok will give
you an estimate of the amount of energy that you can expect to
receive from the cystals that can be mined in a day. You then
decide how long the mining operation lasts, they stay there for
that amount of time and then return.
If the landing party is on an inhabited planet, they will
make a quick estimate of the amount of parts and materials that
they can find so that the repairs to the Enterprise can be
expedited. You will again be asked to decide how much time the
landing party is to spend on the ground. They will stay there
for that amount of time, and then return.
The Transporter cannot be operated, or the Shuttle launched
Copyright (c) Joe Kasser 1989
Chapter 9 PAGE 7 STARTREK THE COMPUTER PROGRAM
if the shields are up. On board sub-system repair goes on while
the landing party are doing their thing. The flowchart for the
transporter is shown in figure 9.8.
Copyright (c) Joe Kasser 1989
