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⌂ ∞ ▽ Elite on the 6502

Tactics: TACTICS (Part 4 of 7)

[Commodore 64 version]

       Name: TACTICS (Part 4 of 7)                                   [Show more]
       Type: Subroutine
   Category: Tactics
    Summary: Apply tactics: Check energy levels, maybe launch escape pod if low
  Deep dive: Program flow of the tactics routine

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




 This section works out what kind of condition the ship is in. Specifically:

   * If this is an Anaconda, consider spawning (22% chance) a Worm (61% of the
     time) or a Sidewinder (39% of the time)

   * Rarely (2.5% chance) roll the ship by a noticeable amount

   * If the ship has at least half its energy banks full, jump to part 6 to
     consider firing the lasers

   * If the ship is not into the last 1/8th of its energy, jump to part 5 to
     consider firing a missile

   * If the ship is into the last 1/8th of its energy, and this ship type has
     an escape pod fitted, then rarely (10% chance) the ship launches an escape
     pod and is left drifting in space



 LDA TYPE               ; If this is not a missile, skip the following
 CMP #MSL               ; instruction
 BNE P%+5

 JMP TA20               ; This is a missile, so jump down to TA20 to get
                        ; straight into some aggressive manoeuvring

 CMP #ANA               ; If this is not an Anaconda, jump down to TN7 to skip
 BNE TN7                ; the following

 JSR DORND              ; Set A and X to random numbers

 CMP #200               ; If A < 200 (78% chance), jump down to TN7 to skip the
 BCC TN7                ; following

 JSR DORND              ; Set A and X to random numbers

 LDX #WRM               ; Set X to the ship type for a Worm

 CMP #100               ; If A >= 100 (61% chance), skip the following
 BCS P%+4               ; instruction

 LDX #SH3               ; Set X to the ship type for a Sidewinder

 JMP TN6                ; Jump to TN6 to spawn the Worm or Sidewinder and return
                        ; from the subroutine using a tail call

.TN7

 JSR DORND              ; Set A and X to random numbers

 CMP #250               ; If A < 250 (97.5% chance), jump down to TA7 to skip
 BCC TA7                ; the following

 JSR DORND              ; Set A and X to random numbers

 ORA #104               ; Bump A up to at least 104 and store in the roll
 STA INWK+29            ; counter, to gives the ship a noticeable roll

.TA7

 LDY #14                ; Set A = the ship's maximum energy / 2
 LDA (XX0),Y
 LSR A

 CMP INWK+35            ; If the ship's current energy in byte #35 > A, i.e. the
 BCC TA3                ; ship has at least half of its energy banks charged,
                        ; jump down to TA3

 LSR A                  ; If the ship's current energy in byte #35 > A / 4, i.e.
 LSR A                  ; the ship is not into the last 1/8th of its energy,
 CMP INWK+35            ; jump down to ta3 to consider firing a missile
 BCC ta3

 JSR DORND              ; Set A and X to random numbers

 CMP #230               ; If A < 230 (90% chance), jump down to ta3 to consider
 BCC ta3                ; firing a missile

 LDX TYPE               ; Fetch the ship blueprint's default NEWB flags from the
 LDA E%-1,X             ; table at E%, and if bit 7 is clear (i.e. this ship
 BPL ta3                ; does not have an escape pod), jump to ta3 to skip the
                        ; spawning of an escape pod

                        ; By this point, the ship has run out of both energy and
                        ; luck, so it's time to bail

 LDA NEWB               ; Clear bits 0-3 of the NEWB flags, so the ship is no
 AND #%11110000         ; longer a trader, a bounty hunter, hostile or a pirate
 STA NEWB               ; and the escape pod we are about to spawn won't inherit
                        ; any of these traits

 LDY #36                ; Update the NEWB flags in the ship's data block
 STA (INF),Y

 LDA #0                 ; Set the AI flag to 0 to disable AI, hostility and
 STA INWK+32            ; E.C.M., so the ship's a sitting duck

 JMP SESCP              ; Jump to SESCP to spawn an escape pod from the ship,
                        ; returning from the subroutine using a tail call