Main loop: Main flight loop (Part 7 of 16)

       Name: Main flight loop (Part 7 of 16)                         [Show more]
       Type: Subroutine
   Category: Main loop
    Summary: For each nearby ship: Check whether we are docking, scooping or
             colliding with it
  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:

     * Check how close we are to this ship and work out if we are docking,
       scooping or colliding with it


 LDA INWK+31            ; Fetch the status of this ship from bits 5 (is ship
 AND #%10100000         ; exploding?) and bit 7 (has ship been killed?) from
                        ; ship byte #31 into A

 LDX TYPE               ; If the current ship type is negative then it's either
 BMI MA65               ; a planet or a sun, so jump down to MA65 to skip the
                        ; following, as we can't dock with it or scoop it

 JSR MAS4               ; Or this value with x_hi, y_hi and z_hi

 BNE MA65               ; If this value is non-zero, then either the ship is
                        ; far away (i.e. has a non-zero high byte in at least
                        ; one of the three axes), or it is already exploding,
                        ; or has been flagged as being killed - in which case
                        ; jump to MA65 to skip the following, as we can't dock
                        ; scoop or collide with it

 LDA INWK               ; Set A = (x_lo OR y_lo OR z_lo), and if bit 7 of the
 ORA INWK+3             ; result is set, the ship is still a fair distance
 ORA INWK+6             ; away (further than 127 in at least one axis), so jump
 BMI MA65               ; to MA65 to skip the following, as it's too far away to
                        ; dock, scoop or collide with

 CPX #SST               ; If this ship is the space station, jump to ISDK to
 BEQ ISDK               ; check whether we are docking with it

 AND #%11000000         ; If bit 6 of (x_lo OR y_lo OR z_lo) is set, then the
 BNE MA65               ; ship is still a reasonable distance away (further than
                        ; 63 in at least one axis), so jump to MA65 to skip the
                        ; following, as it's too far away to dock, scoop or
                        ; collide with

 CPX #MSL               ; If this ship is a missile, jump down to MA65 to skip
 BEQ MA65               ; the following, as we can't scoop or dock with a
                        ; missile, and it has its own dedicated collision
                        ; checks in the TACTICS routine

 LDA BST                ; If we have fuel scoops fitted then BST will be $FF,
                        ; otherwise it will be 0

 AND INWK+5             ; Ship byte #5 contains the y_sign of this ship, so a
                        ; negative value here means the canister is below us,
                        ; which means the result of the AND will be negative if
                        ; the canister is below us and we have a fuel scoop
                        ; fitted

 BMI P%+5               ; If the result is negative, skip the following
                        ; instruction

 JMP MA58               ; If the result is positive, then we either have no
                        ; scoop or the canister is above us, and in both cases
                        ; this means we can't scoop the item, so jump to MA58
                        ; to process a collision