Main loop: Main flight loop (Part 9 of 16)

       Name: Main flight loop (Part 9 of 16)                         [Show more]
       Type: Subroutine
   Category: Main loop
    Summary: For each nearby ship: If it is a space station, check whether we
             are successfully docking with it
  Deep dive: Program flow of the main game loop
             Docking checks
    Context: See this subroutine in context in the source code
 References: This subroutine is called as follows:
             * ESCAPE calls via GOIN
             * WARP calls via GOIN


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

   * Process docking with a space station

 For details on the various docking checks in this routine, see the deep dive
 on "Docking checks".


 Other entry points:

   GOIN                 We jump here from part 3 of the main flight loop if the
                        docking computer is activated by pressing "C"


.ISDK

 LDA K%+NIK%+36         ; 1. Fetch the NEWB flags (byte #36) of the second ship
 AND #%00000100         ; in the ship data workspace at K%, which is reserved
 BNE MA622              ; for the sun or the space station (in this case it's
                        ; the latter), and if bit 2 is set, meaning the station
                        ; is hostile, jump down to MA622 to fail docking (so
                        ; trying to dock at a station that we have annoyed does
                        ; not end well)

 LDA INWK+14            ; 2. If nosev_z_hi < 214, jump down to MA62 to fail
 CMP #214               ; docking, as the angle of approach is greater than 26
 BCC MA62               ; degrees

 JSR SPS1               ; Call SPS1 to calculate the vector to the planet and
                        ; store it in XX15

 LDA XX15+2             ; Set A to the z-axis of the vector

                        ; This version of Elite omits check 3 (which would check
                        ; the sign of the z-axis)

 CMP #89                ; 4. If z-axis < 89, jump to MA62 to fail docking, as
 BCC MA62               ; we are not in the 22.0 degree safe cone of approach

 LDA INWK+16            ; 5. If |roofv_x_hi| < 80, jump to MA62 to fail docking,
 AND #%01111111         ; as the slot is more than 36.6 degrees from horizontal
 CMP #80
 BCC MA62

.GOIN

 JSR ResetMusicAfterNMI ; Wait for the next NMI before resetting the current
                        ; tune to 0 (no tune) and stopping the music

                        ; If we arrive here, we just docked successfully

 JMP DOENTRY            ; Go to the docking bay (i.e. show the ship hangar)

.MA62

                        ; If we arrive here, docking has just failed

 LDA auto               ; If the docking computer is engaged, ensure we dock
 BNE GOIN               ; successfully even if the approach isn't correct, as
                        ; the docking computer algorithm isn't perfect (so this
                        ; fixes the issue in the other versions of Elite where
                        ; the docking computer can kill you)

.MA622

 LDA DELTA              ; If the ship's speed is < 5, jump to MA67 to register
 CMP #5                 ; some damage, but not a huge amount
 BCC MA67

 JMP DEATH              ; Otherwise we have just crashed into the station, so
                        ; process our death