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⌂ ∞ ▽ Elite on the BBC Micro and NES

Moving: MVEIT (Part 9 of 9)

[BBC Master version]

       Name: MVEIT (Part 9 of 9)                                     [Show more]
       Type: Subroutine
   Category: Moving
    Summary: Move current ship: Redraw on scanner, if it hasn't been destroyed

    Context: See this subroutine in context in the source code
 Variations: See code variations for this subroutine in the different versions
 References: No direct references to this subroutine in this source file




 This routine has multiple stages. This stage does the following:

   * If the ship is exploding or being removed, hide it on the scanner

   * Otherwise redraw the ship on the scanner, now that it's been moved



.MV5

 LDA INWK+31            \ Fetch the ship's exploding/killed state from byte #31

 AND #%10100000         \ If we are exploding or removing this ship then jump to
 BNE MVD1               \ MVD1 to remove it from the scanner permanently

 LDA INWK+31            \ Set bit 4 to keep the ship visible on the scanner
 ORA #%00010000
 STA INWK+31

 JMP SCAN               \ Display the ship on the scanner, returning from the
                        \ subroutine using a tail call

.MVD1

 LDA INWK+31            \ Clear bit 4 to hide the ship on the scanner
 AND #%11101111
 STA INWK+31

 RTS                    \ Return from the subroutine