Routines
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87AF: Update Enemy Spawning
Used by the routine at RunLife.
Called once a frame to decide whether to start another enemy. A new enemy is started every eight calls, with a special enemy started part of the way through the countdown, as long as fewer than eight enemies are alive.
UpdateEnemySpawning 87AF LD A,($8E2B) Fetch the number of enemies that are alive from 8E2B.
87B2 CP $08 Return if there are eight of them.
87B4 RET NC
87B5 LD A,($87F5) Fetch the bonus timer from 87F5.
87B8 AND A Test it.
87B9 JR NZ,UpdateEnemySpawning_Timer Jump to UpdateEnemySpawning_Timer if the timer is running.
87BB LD A,($9BCB) Fetch the random seed.
87BE CP $6A Jump to UpdateEnemySpawning_Countdown if it is not the same.
87C0 JR NZ,UpdateEnemySpawning_Countdown
87C2 LD A,($9BCC) Fetch the second byte of the seed.
87C5 AND %00000011 Test the bottom two bits.
87C7 JR NZ,UpdateEnemySpawning_Countdown Jump to UpdateEnemySpawning_Countdown if they are not zero.
87C9 OR %10000000 Set bit 7 of A, which is zero.
87CB LD ($87F5),A Start the bonus timer.
87CE JR UpdateEnemySpawning_Countdown Jump to UpdateEnemySpawning_Countdown.
UpdateEnemySpawning_Timer 87D0 DEC A Count the bonus timer down.
87D1 LD ($87F5),A
UpdateEnemySpawning_Countdown 87D4 LD A,($8790) Count down the spawn timer in 8790.
87D7 DEC A
87D8 LD ($8790),A
87DB CP $07 Jump to SpawnSpecialEnemy if it is 07.
87DD JP Z,SpawnSpecialEnemy
87E0 AND A Return if the countdown has not reached zero.
87E1 RET NZ
87E2 LD A,$08 Restart the countdown at eight.
87E4 LD ($8790),A
This entry point is used by the routine at UpdateEnemies.
UpdateEnemySpawning_Spawn 87E7 LD A,($8791) Fetch the number of slots to search from 8791.
87EA LD IX,$9974 Use the first enemy slot.
87EE CALL FindFreeSlot Search for a free enemy slot.
87F1 JP Z,SpawnEnemy Spawn an enemy if there is a free slot.
87F4 RET Return.
87F5 DEFB $00
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