SUB-HUNT
Games Computing, Issue Oct. 1984 - Pages 82 to 87
By I & B Billups.

Note: Program only works under Issue 2 keyboard emulation (IN commands on program to read keyboard). It can be easily adapted to work on rest of ZX models/boards by changing IN parameters in lines 200 and 240.



"Sub-Hunt" is an arcade type game that will Run on the 16K ZX Spectrum. It has full arcade features including high score table and extended play.

The idea of the game is to destroy the submarines by lining up the greater-than sign at the side of the screen with the submarine and then dropping your depth charge. The depth charge will explode at the height set by the greater-than sign. Use keys 'Q' and 'Z' to move the greater-than sign up and down the side of the screen respectively. Key 'I' will drop a depth charge.

At the top of the screen is PRINTed two scores. Your score and the high score. If your score is greater than the high score, your score will go white. When you hit a submarine you will be
given points; the deeper the submarine is the more points you will get. You will get double points if you hit the submarine in the centre.

At the side of the screen is a fuel scale that will gradually go down. When the fuel runs out the game will end, unless you have achieved extended play. Extended play is awarded at 5000 points. When your score reaches 5000 "extended play" will be PRINTed on the screen momentarily, and when your fuel runs out "extended play" will again be PRINTed and you will be given twice as much fuel as you had when you reached 5000 points; once into an extended play your fuel will be PRINTed in
red.

Occasionally a white submarine will appear at the bottom of the screen. This is a bonus 'Ghost Sub' and it is worth 1000 points or even 2000 if you can hit it in the centre. If you press key 'M' your ship will thrust but you will use up a lot more fuel.

When the game starts, a tune will be played. A different tune will be played at the end of the game.

When the game has finished, providing your score is greater than and you are in the top ten scores, you will be asked to enter your initials. The letters will rotate in alphabetical order, forwards or backwards, when you press keys 'Q' or 'I'. When the correct letter is selected, press key 'M' and go on to the next letter. When you have entered all three initials, the high score table will be displayed. The initials that you have just entered will appear on the table in white.

Another game will start after 1 second or when any key is pressed.


RUNdown

Lines		Action
Pre-game routine

130-150 	Clear the screen and fill
		it with cyan (5) water
		and the blue (1) fuel
		scale.
170-180		Initialize all variables
		that require re-setting
		before each game.
		Other variables are set
		during the initialisation
		routine (line 1000 onwards).

Main game loop
190		PRINT cursor (>) at correct position and
		PRINT spaces above and below it to erase its
		last image.
200		Allow cursor's position to be altered by keys
		'Q' and 'Z'. Note that whenever necessary, IN
		has been used instead of INKEY$ (see chapter
		23 of manual) so that one or more keys can
		be read simultaneously.
210		PRINT boat followed by 2 spaces to erase its last image.
220		PRINT submarine followed by a space to
		erase its last image, if submarine is at
		maximum depth (20) then PRINT it in white (7).
230		If a depth charge is in the water then GOTO
		the relevant sub-routine (336-380, see next
		section). Note that this routine returns to line
		250, thus not allowing 290 two depth charges in
		the water at the same time.
240		Allow a new depth charge to be dropped. (key 'I').
250		Increment variables 'tf' and if player wishes to
		abort game then GOTO 390, the after game
		routine.
260		If 'tf' is now greater than or equal to 3 then
		reset it to 0, erase the top part of the fuel
		scale and decrement the 320 variable 't' (fuel remaining.)
265		If extended play has just been achieved
		then call routine at line 720 to indicate this to the
		player and LET the variable 'Z' equal the
		amount of fuel you have remaining (t). 
270 		If fuel has run out, extended play has not
		yet been used, and score is over or equal to
		5000 points then call the routine to line 720
		again and GOTO 680, which gives extended play.
275		If fuel has run out then GOTO 390, the after game routine.
280		Move submarine and boat and check if hold (key 'H') is pressed.
290		If thrust (key 'M') is pressed then move boat
		another step and decrease fuel by another 2 steps.
300		If the submarine has reached the far right of
		the screen, then erase it, reset it to the start of
		its path and give it a new, random height.
310		If the ship has reached the far left of the
		screen, then erase it, and reset it to the start
		of its path.
320		PRINT score and high score. If score is greater
		than high score, then PRINT it in white (7).
325		If this is the first time around the loop, then
		play introductory tune (line 560 ) before continuing.
327		Return to the start of the loop (line 190).

Depth charge routine

330		Set all variables used by this section.
340		Increment the variable that controls the depth
		of the missile. PRINT relevant character (first
		character of a$) below a space to erase its last image.
350		Re-shuffle the characters of a$ to
		bring the next character needed to the front of
		the string.
360		If a depth charge has reached the bottom of
		the screen or the height of the cursor then erase it.
370		Check for hits, award scores. BEEP, erase any
		sunken submarines, reset them to the far
		left of the screen and give them a new random height.
380		Return from routine (line 250).

After game routines

390-400		Call depressing tune (line 570) and compare
		last score with the 10 held in the table in turn.
		If the score does not rank then GOTO 530.
410		Clear the screen.
420-422		PRINT instructions in teletype style. Note that
		in all such routines a key press will terminate
		the effect and simply PRINT (though without
		colour) the remaining text.
425-490		Form the arcade style entering of the initials.
		Line 430 PRINTs the letters, lines 440-460
		alter them according to key presses, line 470 is
		a simple delay loop, line 480 fixes an initial,
		moving to the next, and line 490 returns to line
		430 completing the cycle.
500		Shift all the scores in the table below the
		latest one down 1 position in the table,
		discarding the lowest score.
510-520		Place latest score and initials in the table at
		the correct point.
530		Tow on words 'todays greatest' behind the
		ship, which then chugs off.
540		PRINT scores (preceeded by 0's if
		necessary) and initials of top 10 players.
		PRINT latest score initials in white.
550		PAUSE (10 seconds), clear the screen and
		start a new game.

Game tunes

560		Play before game 'cheery' tune.
570		Play after game 'depressing' tune.

Instructions

580-590		Tow on words 'sub hunt' behind the
		submarine (line 580) which then chugs off
		(line 590).
620-660		PRINT the first sheet of instructions in teletype
		style.
670-675		Wait for a key press then PRINT the second
		sheet of instructions in teletype style. Wait for
		a key press then clear the screen and RETURN (line 1170).

Extended play routine

680-710 	Decrease extremely large figure (z).
681		Increase extremely small figure (z).
685		Redraw fuel scale to the required height.
690-700		Reset variables.
710		GOTO 280.

PRINT 'EXTENDED PLAY' routine

720		Set PAPER colour to cyan (5)
730-780		PRINT and erase the words 'EXTENDED PLAY' five times.
790		Set PAPER colour back to green (4)
800		RETURN.

Initialise
1010		Set screen colours.
1020-1040	Create graphics. Note that my method of
		creating graphics is shorter than the usual
		ones used.
1050-1110	Data for U.D.G's.
1130-1160	Initialise strings containing instructions.
1165		Initialise graphic strings and the arrays which
		hold the high scores and initials. If instructions
		are required then GOTO the subroutine at line 580.


GRAPHICS
Lines		Graphic

130		29 inverse spaces, 1 space, 1 inverse space
210		Graphics A,B,C and 2 spaces.
220		1 space and Graphics D,E,F.
530		Graphics A,B,C and 1 space,
		Graphics B,C and 1 space,
		Graphic C and one space,
		1 space.
590		1 space and Graphics D,E,F,
		1 space and Graphics D,E,
		1 space and Graphic D,
		1 space
1165		Graphics A,B,C,G and 8 spaces,
		12 spaces and Graphics G,D,E,F.

VARIABLES

a		Used for defining graphics.
a$		String containing the four stages of the rotating bomb.
c(x)		Three element array containing the character
		codes of the three letters being entered as initials
		minus 65.
d		'x' co-ordinate of depth charge.
dc		'y' co-ordinate of depth charge.
d(x)		Eleven element array containing the 11 highest
		scores.
d$(x,y)		Eleven by 3 element array containing the initials of
		the 11 high scorers.
ef		Flag to show if extended play has been awarded
		(1 = yes)
e$		High score table title
f		Flag to show if depth charge has been dropped.
f		Control variable of delay loop (independent of its
		other use).
f$		Instructions title.
g		First set of instructions.
hc		Height of cursor.
hs		Height of submarine.
h$		Second set of instructions.
i$		Terminator of first screen of instructions.
j$		Second screen of instructions.
k$		Terminator of instructions.
l$		High score instructions title.
m$		High score instructions.
n		General purpose control variable.
n		Position of latest score in table.
pb		'x' co-ordinate of boat.
pf		Flag to show if 'EXTENDED PLAY'
		message has been shown.
ps		'x' co-ordinate of submarine.
s		Score of current player.
sf		Flag to show if this is the
		first revolution of the main
		loop.
t		Fuel remaining: Also corresponds to the 'y' coordinate
		of the next points of the fuel scale to be erased.
tf		Counter of number of times the main loop has
		been executed: used in decreasing the players fuel.
z		Value of 't' when extended play achieved.


(CC) 2021, TAP and info created by Ignacio Prini (Spain)