Gameplay: ApplyTactics (Part 8 of 10)

       Name: ApplyTactics (Part 8 of 10)                             [Show more]
       Type: Subroutine
   Category: Gameplay
    Summary: If the drain timer has run down, either drain the target's energy
             or jump to part 9 to create a meanie; or start the drain timer
  Deep dive: Enemy timers and state variables
    Context: See this subroutine in context in the source code
 References: No direct references to this subroutine in this source file


.tact19

                        \ If we get here then there is a suitable target for the
                        \ enemy to drain, and the target's object number is in Y

 TYA                    \ Store the target number in enemyTarget in the enemy's
 STA enemyTarget,X      \ data, so it is set as the enemy's target going forward

 LDA targetVisibility   \ Store the target's visibility in enemyVisibility for
 STA enemyVisibility,X  \ this enemy

 LDA enemyDrainTimer,X  \ If enemyDrainTimer for this enemy is non-zero then it
 CMP #1                 \ is either counting down or has counted down, so jump
 BCS tact21             \ to tact21 to process this

                        \ If we get here then enemyDrainTimer is zero, so we
                        \ restart the timer from 120

 LDA #120               \ Set enemyDrainTimer for this enemy to 120 so the enemy
 STA enemyDrainTimer,X  \ doesn't drain energy for another 120 timer ticks
                        \ (120 * 0.06 = 7.2 seconds)

.tact20

 JMP MoveOnToNextEnemy  \ Jump to MoveOnToNextEnemy to stop applying tactics to
                        \ this enemy and set things up so we move on to the next
                        \ enemy in the next iteration of the gameplay loop

.tact21

 BNE tact20             \ We jump knowing that the enemyDrainTimer for the enemy
                        \ is 1 or greater, so this jumps to tact20 to move on to
                        \ the next enemy when enemyDrainTimer is greater than 1
                        \ and is still counting down

                        \ If we get here then enemyDrainTimer for the enemy has
                        \ counted down to 1, so we need to process that

 LDA targetVisibility   \ If bit 7 of targetVisibility is clear then the enemy
 BPL tact22             \ can't see the tile containing the enemy's target (but
                        \ we know it can see the enemy object as otherwise we
                        \ wouldn't have reached this point), so jump to part 9
                        \ to consider turning a tree into a meanie

                        \ If we get here then the enemy can see the tile
                        \ containing the target, so it can drain its target of
                        \ energy

 JSR DrainObjectEnergy  \ Drain energy from the target object into the enemy,
                        \ transforming it into an object with an energy level
                        \ of one unit less (if applicable)
                        \
                        \ This updates enemyEnergy with the drained energy, so
                        \ it can be expended back onto the landscape later on
                        \
                        \ It also sets X to the object number of the target that
                        \ has been drained of energy (and which has therefore
                        \ been transformed into a different object type)

 LDY enemyObject        \ Set enemyTacticTimer for the enemy to 30 so we wait
 LDA #30                \ for 30 * 0.06 = 1.8 seconds before applying tactics
 STA enemyTacticTimer,Y \ to the enemy again

 BCS tact27             \ If DrainObjectEnergy set the C flag then the enemy
                        \ just drained the player object, so jump to
                        \ MoveOnToNextEnemy via tact27 to stop applying tactics
                        \ to this enemy and set things up so we move on to the
                        \ next enemy in the next iteration of the gameplay loop

 JMP tact25             \ Otherwise it wasn't the player object being drained,
                        \ so jump to tact25 in part 10 with X set to the number
                        \ of the object that was drained so we update it
                        \ on-screen with a dithered effect (as it has now been
                        \ transformed into a different type of object) and
                        \ return from the subroutine