Escape by Nick Shcherbyna

  
+----------------- PUR-80 BASIC GAME for Mattel Aquarius -----------
| (c) 2021 Nick Shcherbyna (Lviv, UA)     computer.history.lviv@gmail.com |
+-------------------------------------------------------------------
| Instructions /                                                                                                                     |
| You are an alien imprisoned in the underground concentration camp known 
| as HANGAR-18.  There are five levels with six floors each, patrolled by 
| bots.  You have to avoid sentinels, otherwise mission will restart from 
| scratch.  Fortunately bots are a bit dumb.  Run as fast as possible and 
| climb up on the ladders using [O]-left, [P]-right, [A]-up and [Z]-down. 
|                                                                         
| Use real hardware or VirtualAquarius emulator:                          
|                              https://www.zophar.net/download_file/32834 
|                                                                         
| Use either Util->Paste to copy the BASIC source from file, or CLOAD the 
| tape image using File->Play Cassette File... Then RUN the game program. 
|                                                                         
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| Source Code Explained /                                                 
|-----------------------                                                  
|                                                                         
| Variables:                                                              
| (X, Y) - Alien coordinates                                              
| Z      - Alien address in VRAM                                          
| B      - Saved character in place of alien                              
| C      - Character below of alien                                       
| (U, V) - Sentinel coordinates                                           
| W      - Sentinel address in VRAM                                       
| D      - Saved character in place of sentinel                           
| E      - Character below of sentinel                                    
| H      - Ladder character code                                          
| M      - Floor character code                                           
| S      - Current level minus 1                                          
| K      - Shifted keycode                                                
| R      - Random value                                                   
| A$     - Beep character                                                 
|                                                                         
| Lines:                                                                  
| 0 Init VRAM address (bottom right), randomize if (re)start, iterate all 
|   screen characters.                                                    
| 1 Init variables for procedural generation: L for ladder, F for floor.  
| 2 Calculate character and display it. Init alien and bot coordinates.   
| 3 Calculate bot VRAM addr. Check for game over condition and restart.   
| 4 Calculate alien VRAM addr. Put alien sprite, poll keyboard.           
| 5 Determine new alien position. Check whether level is completed.       
| 6 finalize new alien position. Start dealing with sentinel.             
| 7 Put sentinel sprite, determine new vertical position.                 
| 8 Determine new horizontal position. Delay, restore characters in place 
|   of sprites.                                                           
| 9 Display message, end game if all levels completed.                    
|                                                                         
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| Source Code Listing /                                                   
|---------------------                                                    
| Note: Microsoft BASIC in Mattel Aquarius limits line of code to just 72 
|       characters, so the program below is effectively PUR-72 ;-)        
|         111111111122222222223333333333444444444455555555556666666666777 
|123456789012345678901234567890123456789012345678901234567890123456789012 
|         |         |         |         |         |         |         |   
|0A=13248:FORY=0TO24:FORX=1TO38:Z=YAND3:R=RND(2*(S=0)+X+Y):L=PEEK(A+X+40) 
|1H=172:M=134:L=Z=1ANDL=MANDC<>HANDR<.2ORZ<>1ANDL=H:F=Z=LAND(C=32ORR<.98) 
|2C=32-102*(Y=0ORF)-140*L:POKEA+X,C:NEXTX:A=A-40:NEXTY:U=38:V=4:X=1:Y=6*V 
|3W=A+40*V+U:A$=CHR$(7):IFX=UANDY=VTHENPOKEW,209:?A$;A$;A$;CHR$(11);:RUN! 
|4Z=A+40*Y+X:B=PEEK(Z):C=PEEK(Z+40):POKEZ,146+(X+YAND1):K=PEEK(14346)-111 
|5X=X+(X>1ANDK=0ANDC>32)-(X<38ANDK=1ANDC>32):Y=Y+(B=HANDK=-14):IFY=0THEN9 
|6Y=Y-(C=32ORC=HANDK=11)::D=PEEK(W)::E=PEEK(W+40)::F=14+5*(U+VAND-(E>32)) 
|7POKEW,F-11*(E=32):L=(V<YANDE<>MORE=32)-(V>YANDD=H):REM(c)NickShcherbyna 
|8U=U+(L=0)*SGN(U-X):V=V-L:FORI=5*STO50:NEXT:POKEZ,B:POKEW,D:GOTO3ESCAPE! 
|9S=S+1:?CHR$(11);"CONGRATS! Level";S;"/5 completed!";A$;A$;A$:IFS<5THEN0 
|                                                                         
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