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⌂ ∞ ▽ Elite on the BBC Micro and NES

Dashboard: ClearScanner

[NES version, Bank 7]

       Name: ClearScanner                                            [Show more]
       Type: Subroutine
   Category: Dashboard
    Summary: Remove all ships from the scanner and hide the scanner sprites

    Context: See this subroutine in context in the source code
 References: This subroutine is called as follows:
             * RES2 calls ClearScanner
             * ShowScrollText calls ClearScanner
             * TT18 calls ClearScanner
             * TT66 calls ClearScanner




.ClearScanner

 LDX #0                 ; Set up a counter in X to work our way through all the
                        ; ship slots in FRIN

.csca1

 LDA FRIN,X             ; Fetch the ship type in slot X

 BEQ csca3              ; If the slot contains 0 then it is empty and we have
                        ; checked all the slots (as they are always shuffled
                        ; down in the main loop to close up and gaps), so jump
                        ; to csca3WS2 as we are done

 BMI csca2              ; If the slot contains a ship type with bit 7 set, then
                        ; it contains the planet or the sun, so jump down to
                        ; csca2 to skip this slot, as the planet and sun don't
                        ; appear on the scanner

 JSR GINF               ; Call GINF to get the address of the data block for
                        ; ship slot X and store it in INF

 LDY #31                ; Clear bit 4 in the ship's byte #31, which hides it
 LDA (INF),Y            ; from the scanner
 AND #%11101111
 STA (INF),Y

.csca2

 INX                    ; Increment X to point to the next ship slot

 BNE csca1              ; Loop back up to process the next slot (this BNE is
                        ; effectively a JMP as X will never be zero)

.csca3

 LDY #44                ; Set Y so we start hiding from sprite 44 / 4 = 11

 LDX #27                ; Set X = 27 so we hide 27 sprites

                        ; Fall through into HideSprites to hide 27 sprites
                        ; from sprite 11 onwards (i.e. the scanner sprites from
                        ; 11 to 37)