Main loop: Main flight loop (Part 8 of 16)

       Name: Main flight loop (Part 8 of 16)                         [Show more]
       Type: Subroutine
   Category: Main loop
    Summary: For each nearby ship: Process us potentially scooping this item
  Deep dive: Program flow of the main game loop
    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:

     * Process us potentially scooping this item


 CPX #OIL               ; If this is a cargo canister, jump to oily to randomly
 BEQ oily               ; decide the canister's contents

 LDY #0                 ; Fetch byte #0 of the ship's blueprint
 LDA (XX0),Y

 LSR A                  ; Shift it right four times, so A now contains the high
 LSR A                  ; nibble (i.e. bits 4-7)
 LSR A
 LSR A

 BEQ MA58               ; If A = 0, jump to MA58 to skip all the docking and
                        ; scooping checks

                        ; Only the Thargon, alloy plate, splinter and escape pod
                        ; have non-zero high nibbles in their blueprint byte #0
                        ; so if we get here, our ship is one of those, and the
                        ; high nibble gives the market item number of the item
                        ; when scooped, less 1

 ADC #1                 ; Add 1 to the high nibble to get the market item
                        ; number

 BNE slvy2              ; Skip to slvy2 so we scoop the ship as a market item

.oily

 JSR DORND              ; Set A and X to random numbers and reduce A to a
 AND #7                 ; random number in the range 0-7

.slvy2

                        ; By the time we get here, we are scooping, and A
                        ; contains the type of item we are scooping (a random
                        ; number 0-7 if we are scooping a cargo canister, 3 if
                        ; we are scooping an escape pod, or 16 if we are
                        ; scooping a Thargon). These numbers correspond to the
                        ; relevant market items (see QQ23 for a list), so a
                        ; cargo canister can contain anything from food to
                        ; computers, while escape pods contain slaves, and
                        ; Thargons become alien items when scooped

 JSR tnpr1              ; Call tnpr1 with the scooped cargo type stored in A
                        ; to work out whether we have room in the hold for one
                        ; tonne of this cargo (A is set to 1 by this call, and
                        ; the C flag contains the result)

 LDY #78                ; This instruction has no effect, so presumably it used
                        ; to do something, but didn't get removed

 BCS MA59               ; If the C flag is set then we have no room in the hold
                        ; for the scooped item, so jump down to MA59 make a
                        ; sound to indicate failure, before destroying the
                        ; canister

 LDY QQ29               ; Scooping was successful, so set Y to the type of
                        ; item we just scooped, which we stored in QQ29 above

 ADC QQ20,Y             ; Add A (which we set to 1 above) to the number of items
 STA QQ20,Y             ; of type Y in the cargo hold, as we just successfully
                        ; scooped one canister of type Y

 TYA                    ; Print recursive token 48 + Y as an in-flight token,
 ADC #208               ; which will be in the range 48 ("FOOD") to 64 ("ALIEN
 JSR MESS               ; ITEMS"), so this prints the scooped item's name

 ASL NEWB               ; The item has now been scooped, so set bit 7 of its
 SEC                    ; NEWB flags to indicate this
 ROR NEWB

.MA65

 JMP MA26               ; If we get here, then the ship we are processing was
                        ; too far away to be scooped, docked or collided with,
                        ; so jump to MA26 to skip over the collision routines
                        ; and move on to missile targeting