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Nukey?


neotokeo2001

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The background color is saved at 2 points in Alien...though in the disassembly, only 1 point can be located by searching for COLUBK: the bonus round...when the foreground and background are both zeroed - BTW the maze is still there ;)

 

LFD55:
      LDA    $80                    ;3
      AND    #$20                   ;2
      BEQ    LFD8D                  ;2
      LDA    #$00                   ;2 black background during bonus stage
      STA    COLUBK                 ;3

 

 

To locate the other point, I just traced the SWCHB equate. In Alien, the colors will be changed to monochrome when B&W is selected (the way that it does this is by using an AND value to strip away bits IF B&W is selected)...

       TXS                           ;2 start with %11111111
      LDA    SWCHB                  ;4
      AND    #$08                   ;2 check B&W
      BNE    LF766                  ;2 if color, skip next line
      LDX    #$0D                   ;2 use %00001101 instead
LF766:
      TXA                           ;2 move that bit pattern to A
      LDY    #$00                   ;2
      BIT    $80                    ;3
      BVC    LF773                  ;2
      LDY    $BF                    ;3
      ORA    #$02                   ;2
      AND    #$F6                   ;2
LF773:
      STA    $9E                    ;3 save the bit pattern to $9E
      STY    $84                    ;3
      LDA    $E8                    ;3
      BNE    LF78F                  ;2
      LDX    #$08                   ;2
LF77D:
      LDA    LFE3C,X                ;4 get value from a table
      EOR    $84                    ;3
      AND    $9E                    ;3 strip away bits when B&W
      STA    $F5,X                  ;4
      CPX    #$07                   ;2
      BCC    LF78C                  ;2
      STA    VBLANK,X               ;4 when X = 7 or 8, save to the color registers

 

So all that really needs changing is the last 2 bytes in table LFE3C...

 

LFE3C:
      .byte $BE; |X XXXXX | $FE3C
      .byte $1E; |   XXXX | $FE3D
      .byte $5E; | X XXXX | $FE3E
      .byte $8E; |X   XXX | $FE3F
      .byte $4E; | X  XXX | $FE40
      .byte $1E; |   XXXX | $FE41
      .byte $8E; |X   XXX | $FE42
      .byte $60; | XX     | $FE43 wall color in maze section
      .byte $84; |X    X  | $FE44 screen color in maze section

 

 

 

VERY rough disassembly + cfg...

Alien.zip

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