GRAVITY

The following article was printed in July 1991 of the magazine „8000 PLUS"

A labyrinth game programmed in BASIC

GRAVITY By Tim Granger, Cambridge

There are many PCW maze games, but most lack a purpose other than escape.

Gravity does not. Your task in the maze is to collect as many precious gems as you can. These are shown on screen by the letter 'O', and are collected by walking into them. You are the blob at the top left of the screen when the game begins, and you move by pressing the cursor keys. There are also small squares in the maze, representing blocks which may prevent you from entering a new corridor. You can get past them only if you have some gems, and each block destroyed costs one gem.

A real gem - Gravity's 'Outrageous' level

Look out for monsters too! They appear as a sort of cross shape, and if you touch them the game ends. A shot, costing three gems, will get rid of them. Move your playing piece in the monster's direction and press [SPACE].

When a maze is drawn, you may be locked in a room. To get out, shoot at one of the walls to turn it into a monster. Shoot him, and he becomes a block. Fortunately, you are given the seven gems needed to get through a wall at the start of the game.

Unlike conventional mazes, this one is drawn on a vertical axis, so here, up really does mean up. The most natural direction in which you can travel is down, and down is exactly where you go if you don't touch any of the other cursor keys. This tendency to fall towards the bottom of the screen is caused by gravity - hence game's name.

There are four levels of play, from 'Easy' to 'Outrageous'. Each skill level is divided into ten levels of increasing difficulty, monsters and blocks, and decreasing numbers of gems. Exit from the current level at bottom right hand corner of the maze. Pressing 'Q' will kill your character and end the game.

10 INPUT "Enter skill level, 1-4 (1=Easy) ",k                                        1564
20 h=1:sc=0:ge=7:e$=CHR$(27):DEF FNT$(x,y)=e$+"Y"+CHR$(32+x)+CHR$(31+y)              1CA9
30 DATA Easy,.5,8,10,5,Medium,1,10,16,10,Hard,1.5,10,25,15,
   Outrageous,2.5,14,30,25                                                           2002
40 DATA 6,5,6,6,6,9,7,11,8,13,8,13,7,10,6,9,5,7,4,8,31,6,30,1,0,-1,1,0,0,1,-1,0      1557
50 DATA 149,154,149,154,149,187,128,143                                              0C0D
60 DIM ad[4,2],pt$[32,65],i[4,4],n[10,3]                                             1290
70 FOR a=1 TO 4:READ t$[a]:FOR b=1 TO 4:READ i[a,b]:NEXT b,a:RANDOMIZE PEEK (64504!) 27E7
80 FOR a=1 TO 10:READ p,q:n[a,1]=3*p:n[a,2]=2*q:n[a,3]=2*a:NEXT a                    1E42
90 FOR a=1 TO 4:READ ch[a]:NEXT a:FOR a=1 TO 4:FOR b=1 TO 2:
   READ ad[a,b]:NEXT b,a                                                             2710
100 FOR a=1 TO 5:READ q:a$[a]=CHR$(q):NEXT a:FOR a=1 TO 3:
    READ p:s$[a]=CHR$(p):NEXT a                                                      2817

The program begins by defining the variables used for the level names, the shape of the walls and the objects. This data is read into arrays in lines 70 to 100

110 m=i[k,1]:xc=2*i[k,2]:sd=2*i[k,3]:p=i[k,4]:PRINT e$+"f"+e$+"0"                    1FD7
120 PRINT e$+"E":PRINT FNT$(30,0)t$[k];FNT$(30,15)"Level";h:w=0:
    GOSUB 400:GOSUB 410                                                              233A
130 v=0:FOR a=0 TO xc+2:FOR b=0 TO sd+2:pt$[a,b]=" ":NEXT b,a                        19F5
140 FOR a=1 TO 3:no=INT(xc*sd*m*n[h,a]/400):GOSUB 440:NEXT a                         1C31
150 FOR a=2 TO xc STEP 2:FOR b=2 TO sd STEP 2:z=0:GOSUB 420:NEXT b,a                 1F1B
160 FOR a=3 TO xc-1 STEP 2:FOR b=3 TO sd-1 STEP 2:z=1:GOSUB 420:NEXT b,a             2198
170 FOR a=2 TO sd STEP 2:pt$[1,a]=CHR$(154):pt$[xc+1,a]=CHR$(154):NEXT a             1F6C
180 FOR a=2 TO xc STEP 2:pt$[a,1]=CHR$(149):pt$[a,sd+1]=CHR$(149):NEXT a             1F92
190 pt$[2,2]=" ":pt$[2,3]=" ":pt$[3,2]=" ":FOR a=1 TO xc+1 STEP 2:
    FOR b=1 TO sd+1 STEP 2                                                           23CC
200 t=0:FOR c=1 TO 4:IF pt$[a+ad[c,1],b+ad[c,2]]<>" " THEN t=t+2^(4-c)               1D7F

The above section of code introduces you to each new level by displaying the number of gems you have. Lines 140 to 180 work out where the walls will be placed and the up facing arrow at the end of line 200 is produced by pressing [ALT] U

210 NEXT c:pt$[a,b]=CHR$(144+t):NEXT b,a                                             134F
220 FOR a=1 TO xc+1:FOR b=1 TO sd+1:PRINT pt$[a,b];:
    NEXT b:PRINT:NEXT a:x=2:y=2                                                      2A0D
230 PRINT FNT$(x,y)CHR$(188):IF x=xc AND y=sd THEN h=h+1:
    IF h<11 THEN 120 ELSE 340                                                        23B6
240 v=v+1:f$=INKEY$:IF INT(v/50)=v/50 THEN f$=CHR$(30)                               16CE
250 IF f$="" THEN 240 ELSE f=ASC(f$):IF d>0 THEN d1=d                                1642
260 d=0:FOR a=1 TO 4:IF ch[a]=f THEN d=5-a                                           11C6
270 NEXT a:IF f=113 OR f=81 THEN r=143:GOTO 310                                      1517
280 IF f=32 AND ge>2 THEN w=-3:GOSUB 400:i=x:j=y:GOSUB 350:
    GOTO 240 ELSE IF d=0 THEN 240                                                    2857
290 r=ASC(pt$[x+ad[d,1],y+ad[d,2]]):IF r=32 THEN 330                                 1848
300 IF r=187 THEN w=1:GOSUB 400:pt$[x+ad[d,1],y+ad[d,2]]=" ":GOTO 330                1E78

The program looks to the keyboard for input and moves your character in the direction of the cursor key you pressed. If you press Q, the game will end. This section also calculates how many gems you have.

310 IF r=143 THEN PRINT FNT$(30,35)"You're Dead!";e$+"e":END                         1A31
320 IF r=128 AND ge>0 THEN w=-1:GOSUB 400:pt$[x+ad[d,1],y+ad[d,2]]=" ":
    GOTO 330 ELSE 240                                                                26FE
330 PRINT FNT$(x,y)" ":x=x+ad[d,1]:y=y+ad[d,2]:GOTO 230                              1A1E
340 GOSUB 410:PRINT FNT$(30,35)"End of Skill Level";e$+"e":END                       1C83
350 PRINT FNT$(i,j)" ":PRINT FNT$(x,y)CHR$(188):i=i+ad[d1,1]:j=j+ad[d1,2]            1F91
360 r=ASC(pt$[i,j]):IF r=128 THEN PRINT FNT$(i,j)" ":pt$[i,j]=" ":RETURN             2265
370 IF r=149 OR r=154 THEN PRINT FNT$(i,j)CHR$(143):pt$[i,j]=CHR$(143):RETURN        2477
380 IF r=32 THEN PRINT FNT$(i,j)"+":GOTO 350                                         13F1
390 PRINT FNT$(i,j)CHR$(128):pt$[i,j]=CHR$(128):RETURN                               18A6
400 ge=ge+w:PRINT FNT$(30,60)"Gems:";ge;e$+"H":RETURN                                17A5

Line 310 kills your character if it runs into a monster and the rest of the section erases and re-displays your character when it moves and records which level you are on

This final piece of code displays your score so far (based on the number of gems you have) and randomly calculates the co-ordinates for the walls

[BASIC-Listing]