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⌂ ∞ ▽ Elite on the 6502

Main loop: Main flight loop (Part 12 of 16)

[NES version, Bank 0]

       Name: Main flight loop (Part 12 of 16)                        [Show more]
       Type: Subroutine
   Category: Main loop
    Summary: For each nearby ship: Draw the ship, remove if killed, loop back
  Deep dive: Program flow of the main game loop
             Drawing ships

    Context: See this subroutine in context in the source code
 References: No direct references to this subroutine in this source file




 The main flight loop covers most of the flight-specific aspects of Elite. This
 section covers the following:

   * Continue looping through all the ships in the local bubble, and for each
     one:

     * Draw the ship

     * Process removal of killed ships

   * Loop back up to MAL1 to move onto the next ship in the local bubble



.MA8

 JSR LL9_b1             ; Call LL9 to draw the ship we're processing on-screen

.MA15

 LDY #35                ; Fetch the ship's energy from byte #35 and copy it to
 LDA INWK+35            ; byte #35 in INF (so the ship's data in K% gets
 STA (INF),Y            ; updated)

 LDA INWK+34            ; Fetch the ship's explosion cloud counter from byte #34
 LDY #34                ; and copy it to byte #34 in INF (so the ship's data in
 STA (INF),Y            ; K% gets updated)

 LDA NEWB               ; If bit 7 of the ship's NEWB flags is set, which means
 BMI KS1S               ; the ship has docked or been scooped, jump to KS1S to
                        ; skip the following, as we can't get a bounty for a
                        ; ship that's no longer around

 LDA INWK+31            ; If bit 7 of the ship's byte #31 is clear, then the
 BPL MAC1               ; ship hasn't been killed by energy bomb, collision or
                        ; laser fire, so jump to MAC1 to skip the following

 AND #%00100000         ; If bit 5 of the ship's byte #31 is clear then the
 BEQ MAC1               ; ship is no longer exploding, so jump to MAC1 to skip
                        ; the following

 LDA NEWB               ; Extract bit 6 of the ship's NEWB flags, so A = 64 if
 AND #%01000000         ; bit 6 is set, or 0 if it is clear. Bit 6 is set if
                        ; this ship is a cop, so A = 64 if we just killed a
                        ; policeman, otherwise it is 0

 ORA FIST               ; Update our FIST flag ("fugitive/innocent status") to
 STA FIST               ; at least the value in A, which will instantly make us
                        ; a fugitive if we just shot the sheriff, but won't
                        ; affect our status if the enemy wasn't a copper

 LDA MJ                 ; If we are in witchspace (in which case MJ > 0) or
 ORA demoInProgress     ; demoInProgress > 0 (in which case we are playing the
 BNE KS1S               ; demo), jump to KS1S to skip showing an on-screen
                        ; bounty for this kill

 LDY #10                ; Fetch byte #10 of the ship's blueprint, which is the
 JSR GetShipBlueprint   ; low byte of the bounty awarded when this ship is
 BEQ KS1S               ; killed (in Cr * 10), and if it's zero jump to KS1S as
                        ; there is no on-screen bounty to display

 TAX                    ; Put the low byte of the bounty into X

 INY                    ; Fetch byte #11 of the ship's blueprint, which is the
 JSR GetShipBlueprint   ; high byte of the bounty awarded (in Cr * 10), and put
 TAY                    ; it into Y

 JSR MCASH              ; Call MCASH to add (Y X) to the cash pot

 LDA #0                 ; Print control code 0 (current cash, right-aligned to
 JSR MESS               ; width 9, then " CR", newline) as an in-flight message

.KS1S

 JMP KS1                ; Process the killing of this ship (which removes this
                        ; ship from its slot and shuffles all the other ships
                        ; down to close up the gap)

.MAC1

 LDA TYPE               ; If the ship we are processing is a planet or sun,
 BMI MA27               ; jump to MA27 to skip the following two instructions

 JSR FAROF              ; If the ship we are processing is a long way away (its
 BCC KS1S               ; distance in any one direction is > 224, jump to KS1S
                        ; to remove the ship from our local bubble, as it's just
                        ; left the building

.MA27

 LDY #31                ; Fetch the ship's explosion/killed state from byte #31,
 LDA INWK+31            ; clear bit 6 to denote that an explosion has not been
 AND #%10111111         ; drawn, and copy it to byte #31 in INF (so the ship's
 STA (INF),Y            ; data in K% gets updated)

 LDX XSAV               ; We're done processing this ship, so fetch the ship's
                        ; slot number, which we saved in XSAV back at the start
                        ; of the loop

 INX                    ; Increment the slot number to move on to the next slot

 RTS                    ; Return from the subroutine