Universe: KILLSHP

       Name: KILLSHP                                                 [Show more]
       Type: Subroutine
   Category: Universe
    Summary: Remove a ship from our local bubble of universe
    Context: See this subroutine in context in the source code
 References: This subroutine is called as follows:
             * KS1 calls KILLSHP


 Remove the ship in slot X from our local bubble of universe. This happens
 when we kill a ship, collide with a ship and destroy it, or when a ship moves
 outside our local bubble.

 We also use this routine when we move out of range of the space station, in
 which case we replace it with the sun.

 When removing a ship, this creates a gap in the ship slots at FRIN, so we
 shuffle all the later slots down to close the gap. We also shuffle the ship
 data blocks at K% to reclaim all the memory that the removed ship used to
 occupy.


 Arguments:

   X                    The slot number of the ship to remove

   XX0                  The address of the blueprint for the ship to remove

   INF                  The address of the data block for the ship to remove


.KILLSHP

 STX XX4                ; Store the slot number of the ship to remove in XX4

 JSR HideFromScanner_b1 ; Hide the ship from the scanner

 LDX XX4                ; Set X to the slot number of the ship to remove

 LDA MSTG               ; Check whether this slot matches the slot number in
 CMP XX4                ; MSTG, which is the target of our missile lock

 BNE KS5                ; If our missile is not locked on this ship, jump to KS5

 LDY #108               ; Otherwise we need to remove our missile lock, so call
 JSR ABORT              ; ABORT to disarm the missile and update the missile
                        ; indicators on the dashboard to the pattern number in
                        ; Y (black indicator = pattern 108)

 LDA #200               ; Print recursive token 40 ("TARGET LOST") as an
 JSR MESS               ; in-flight message

.KS5

 LDY XX4                ; Restore the slot number of the ship to remove into Y

 LDX FRIN,Y             ; Fetch the contents of the slot, which contains the
                        ; ship type

 CPX #SST               ; If this is the space station, then jump to KS4 to
 BNE kill1              ; replace the space station with the sun
 JMP KS4

.kill1

 CPX #CON               ; Did we just kill the Constrictor from mission 1? If
 BNE lll                ; not, jump to lll

 LDA TP                 ; We just killed the Constrictor from mission 1, so set
 ORA #%00000010         ; bit 1 of TP to indicate that we have successfully
 STA TP                 ; completed mission 1

 INC TALLY+1            ; Award 256 kill points for killing the Constrictor

.lll

 CPX #HER               ; Did we just kill a rock hermit? If we did, jump to
 BEQ blacksuspenders    ; blacksuspenders to decrease the junk count

 CPX #JL                ; If JL <= X < JH, i.e. the type of ship we killed in X
 BCC KS7                ; is junk (escape pod, alloy plate, cargo canister,
 CPX #JH                ; asteroid, splinter, Shuttle or Transporter), then keep
 BCS KS7                ; going, otherwise jump to KS7

.blacksuspenders

 DEC JUNK               ; We just killed junk, so decrease the junk counter

.KS7

 DEC MANY,X             ; Decrease the number of this type of ship in our little
                        ; bubble, which is stored in MANY+X (where X is the ship
                        ; type)

 LDX XX4                ; Restore the slot number of the ship to remove into X

.KSL1

 SETUP_PPU_FOR_ICON_BAR ; If the PPU has started drawing the icon bar, configure
                        ; the PPU to use nametable 0 and pattern table 0

 INX                    ; On entry, X points to the empty slot we want to
                        ; shuffle the next ship into (the destination), so
                        ; this increment points X to the next slot - i.e. the
                        ; source slot we want to shuffle down

 LDA FRIN,X             ; Copy the contents of the source slot into the
 STA FRIN-1,X           ; destination slot

 BNE P%+5               ; If the slot we just shuffled down is not empty, then
                        ; skip the following instruction

 JMP KS2                ; The source slot is empty and we are done shuffling,
                        ; so jump to KS2 to move on to processing missiles

 TXA                    ; Set Y = X * 2 so it can act as an index into the
 ASL A                  ; two-byte lookup table at UNIV, which contains the
 TAY                    ; addresses of the ship data blocks. In this case we are
                        ; multiplying X by 2, and X contains the source ship's
                        ; slot number so Y is now an index for the source ship's
                        ; entry in UNIV

 LDA UNIV,Y             ; Set SC(1 0) to the address of the data block for the
 STA SC                 ; source ship
 LDA UNIV+1,Y
 STA SC+1

 SETUP_PPU_FOR_ICON_BAR ; If the PPU has started drawing the icon bar, configure
                        ; the PPU to use nametable 0 and pattern table 0

                        ; We have now set up our variables as follows:
                        ;
                        ;   SC(1 0) points to the source's ship data block
                        ;
                        ;   INF(1 0) points to the destination's ship data block
                        ;
                        ;   P(1 0) points to the destination's line heap
                        ;
                        ; so let's start copying data from the source to the
                        ; destination

 LDY #41                ; We are going to be using Y as a counter for the 42
                        ; bytes of ship data we want to copy from the source
                        ; to the destination, so we set it to 41 to start things
                        ; off, and will decrement Y for each byte we copy

.KSL2

 LDA (SC),Y             ; Copy the Y-th byte of the source to the Y-th byte of
 STA (INF),Y            ; the destination

 DEY                    ; Decrement the counter

 BPL KSL2               ; Loop back to KSL2 to copy the next byte until we have
                        ; copied the whole block

                        ; We have now shuffled the ship's slot and the ship's
                        ; data block, so we only have the heap data itself to do

 LDA SC                 ; First, we copy SC into INF, so when we loop round
 STA INF                ; again, INF will correctly point to the destination for
 LDA SC+1               ; the next iteration
 STA INF+1

 SETUP_PPU_FOR_ICON_BAR ; If the PPU has started drawing the icon bar, configure
                        ; the PPU to use nametable 0 and pattern table 0

 JMP KSL1               ; We have now shuffled everything down one slot, so
                        ; jump back up to KSL1 to see if there is another slot
                        ; that needs shuffling down