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⌂ ∞ ▽ Elite on the BBC Micro and NES

Tactics: TACTICS (Part 2 of 7)

[6502 Second Processor version]

       Name: TACTICS (Part 2 of 7)                                   [Show more]
       Type: Subroutine
   Category: Tactics
    Summary: Apply tactics: Escape pod, station, lone Thargon, safe-zone pirate
  Deep dive: Program flow of the tactics routine

    Context: See this subroutine in context in the source code
 Variations: See code variations for this subroutine in the different versions
 References: This subroutine is called as follows:
             * MVEIT (Part 2 of 9) calls TACTICS




 This section contains the main entry point at TACTICS, which is called from
 part 2 of MVEIT for ships that have the AI flag set (i.e. bit 7 of byte #32).
 This part does the following:

   * If this is a missile, jump up to the missile code in part 1

   * If this is the space station and it is hostile, consider spawning a cop
     (6.2% chance, up to a maximum of seven) and we're done

   * If this is the space station and it is not hostile, consider spawning
     (0.8% chance if there are no Transporters around) a Transporter or Shuttle
     (equal odds of each type) and we're done

   * If this is a rock hermit, consider spawning (22% chance) a highly
     aggressive and hostile Sidewinder, Mamba, Krait, Adder or Gecko (equal
     odds of each type) and we're done

   * Recharge the ship's energy banks by 1



 Arguments:

   X                    The ship type



.TACTICS

 LDA #3                 \ Set RAT = 3, which is the magnitude we set the pitch
 STA RAT                \ or roll counter to in part 7 when turning a ship
                        \ towards a vector (a higher value giving a longer
                        \ turn). This value is not changed in the TACTICS
                        \ routine, but it is set to different values by the
                        \ DOCKIT routine

 LDA #4                 \ Set RAT2 = 4, which is the threshold below which we
 STA RAT2               \ don't apply pitch and roll to the ship (so a lower
                        \ value means we apply pitch and roll more often, and a
                        \ value of 0 means we always apply them). The value is
                        \ compared with double the high byte of sidev . XX15,
                        \ where XX15 is the vector from the ship to the enemy
                        \ or planet. This value is set to different values by
                        \ both the TACTICS and DOCKIT routines

 LDA #22                \ Set CNT2 = 22, which is the maximum angle beyond which
 STA CNT2               \ a ship will slow down to start turning towards its
                        \ prey (a lower value means a ship will start to slow
                        \ down even if its angle with the enemy ship is large,
                        \ which gives a tighter turn). This value is not changed
                        \ in the TACTICS routine, but it is set to different
                        \ values by the DOCKIT routine

 CPX #MSL               \ If this is a missile, jump up to TA18 to implement
 BEQ TA18               \ missile tactics

 CPX #SST               \ If this is not the space station, jump down to TA13
 BNE TA13

 LDA NEWB               \ This is the space station, so check whether bit 2 of
 AND #%00000100         \ the ship's NEWB flags is set, and if it is (i.e. the
 BNE TN5                \ station is hostile), jump to TN5 to spawn some cops

 LDA MANY+SHU+1         \ The station is not hostile, so check how many
 BNE TA1                \ Transporters there are in the vicinity, and if we
                        \ already have one, return from the subroutine (as TA1
                        \ contains an RTS)

                        \ If we get here then the station is not hostile, so we
                        \ can consider spawning a Transporter or Shuttle

 JSR DORND              \ Set A and X to random numbers

 CMP #253               \ If A < 253 (99.2% chance), return from the subroutine
 BCC TA1                \ (as TA1 contains an RTS)

 AND #1                 \ Set A = a random number that's either 0 or 1

 ADC #SHU-1             \ The C flag is set (as we didn't take the BCC above),
 TAX                    \ so this sets X to a value of either #SHU or #SHU + 1,
                        \ which is the ship type for a Shuttle or a Transporter

 BNE TN6                \ Jump to TN6 to spawn this ship type and return from
                        \ the subroutine using a tail call (this BNE is
                        \ effectively a JMP as A is never zero)

.TN5

                        \ We only call the tactics routine for the space station
                        \ when it is hostile, so if we get here then this is the
                        \ station, and we already know it's hostile, so we need
                        \ to spawn some cops

 JSR DORND              \ Set A and X to random numbers

 CMP #240               \ If A < 240 (93.8% chance), return from the subroutine
 BCC TA1                \ (as TA1 contains an RTS)

 LDA MANY+COPS          \ Check how many cops there are in the vicinity already,
 CMP #7                 \ and if there are 7 or more, return from the subroutine
 BCS TA22               \ (as TA22 contains an RTS)

 LDX #COPS              \ Set X to the ship type for a cop

.TN6

 LDA #%11110001         \ Set the AI flag to give the ship E.C.M., enable AI and
                        \ make it very aggressive (60 out of 63)

 JMP SFS1               \ Jump to SFS1 to spawn the ship, returning from the
                        \ subroutine using a tail call

.TA13

 CPX #HER               \ If this is not a rock hermit, jump down to TA17
 BNE TA17

 JSR DORND              \ Set A and X to random numbers

 CMP #200               \ If A < 200 (78% chance), return from the subroutine
 BCC TA22               \ (as TA22 contains an RTS)

 LDX #0                 \ Set byte #32 to %00000000 to disable AI, aggression
 STX INWK+32            \ and E.C.M.

 STX NEWB               \ Set the ship's NEWB flags to %00000000 so the ship we
                        \ spawn below will inherit the default values from E%

 AND #3                 \ Set A = a random number that's in the range 0-3

 ADC #SH3               \ The C flag is set (as we didn't take the BCC above),
 TAX                    \ so this sets X to a random value between #SH3 + 1 and
                        \ #SH3 + 4, so that's a Sidewinder, Mamba, Krait, Adder
                        \ or Gecko

 JSR TN6                \ Call TN6 to spawn this ship with E.C.M., AI and a high
                        \ aggression (56 out of 63)

 LDA #0                 \ Set byte #32 to %00000000 to disable AI, aggression
 STA INWK+32            \ and E.C.M. (for the rock hermit)

 RTS                    \ Return from the subroutine

.TA17

 LDY #14                \ If the ship's energy is greater or equal to the
 LDA INWK+35            \ maximum value from the ship's blueprint pointed to by
 CMP (XX0),Y            \ XX0, then skip the next instruction
 BCS TA21

 INC INWK+35            \ The ship's energy is not at maximum, so recharge the
                        \ energy banks by 1