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Routines |
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Used by the routines at RunLife and ExplodeShip.
Updates all nine enemy slots once a frame. The counter at 8F53 tracks the explosion of the player's ship: it counts up from one when the ship is destroyed, the debris is started when it reaches ten, and the ship is gone for good when it has gone past that point.
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| UpdateEnemies | 8D42 | LD A,($8F53) | Fetch the explosion counter from 8F53. | |
| 8D45 | AND A | Test it. | ||
| 8D46 | JR Z,UpdateEnemies_Debris | Jump to UpdateEnemies_Debris if the ship is intact. | ||
| 8D48 | INC A | Increase the counter... | ||
| 8D49 | LD ($8F53),A | ...and store it. | ||
| UpdateEnemies_Debris | 8D4C | CP $0A | Has the counter reached ten? | |
| 8D4E | CALL Z,ExplodePlayerShip | Start the debris if so. | ||
| 8D51 | LD A,($8F53) | Fetch the explosion counter again. | ||
| 8D54 | CP $0A | Is it ten or more? | ||
| 8D56 | CALL NC,PlayExplosionSound | Play the sound of the explosion if so. | ||
| 8D59 | LD A,($5C40) | Fetch the value from Variables. | ||
| 8D5C | LD ($8CB1),A | Store it in 8CB1. | ||
| 8D5F | XOR A | Clear A. | ||
| 8D60 | LD ($8E2B),A | Clear the number of active enemies in 8E2B. | ||
| 8D63 | LD ($5C40),A | Clear Variables. | ||
| 8D66 | LD A,($8D3C) | Fetch the value from 8D3C. | ||
| 8D69 | LD ($8E2B),A | Store it in 8E2B. | ||
| 8D6C | LD IX,$9974 | Use the first enemy slot. | ||
| 8D70 | LD B,$09 | Set the counter for nine slots. | ||
| UpdateEnemies_Loop | 8D72 | PUSH BC | Save the slot counter. | |
| 8D73 | PUSH IX | Save the address of the slot. | ||
| 8D75 | LD A,(IX+$00) | Fetch the type of the object in the slot. | ||
| 8D78 | INC A | Increment it. | ||
| 8D79 | JP Z,UpdateEnemies_Skip | Skip the slot if it is free. | ||
| 8D7C | LD A,(IX+$17) | Fetch the second set of flags of the object. | ||
| 8D7F | AND %11110000 | Keep the top four bits. | ||
| 8D81 | JR Z,UpdateEnemies_Exploding | Jump to UpdateEnemies_Exploding if they are zero. | ||
| 8D83 | SUB $10 | Subtract one from the top four bits... | ||
| 8D85 | LD B,A | ...and store them back with the bottom four bits. | ||
| 8D86 | LD A,(IX+$17) | |||
| 8D89 | AND $0F | |||
| 8D8B | OR B | |||
| 8D8C | LD (IX+$17),A | |||
| UpdateEnemies_Exploding | 8D8F | LD A,($8F53) | Fetch the explosion counter from 8F53. | |
| 8D92 | AND A | Test it. | ||
| 8D93 | JR Z,UpdateEnemies_Update | Jump to UpdateEnemies_Update if the ship is intact. | ||
| 8D95 | CP $04 | Jump to UpdateEnemies_Update if the counter is four or higher. | ||
| 8D97 | JR NC,UpdateEnemies_Update | |||
| 8D99 | SET 3,(IX+$17) | Otherwise set bit 3 of the second set of flags. | ||
| UpdateEnemies_Update | 8D9D | LD A,$50 | Set the collision effects in 8E2C to 50. | |
| 8D9F | LD ($8E2C),A | |||
| 8DA2 | LD A,($8E2B) | Add one to the number of active enemies in 8E2B. | ||
| 8DA5 | INC A | |||
| 8DA6 | LD ($8E2B),A | |||
| 8DA9 | CALL ResetSprites | Reset the collision state. | ||
| 8DAC | BIT 7,(IX+$10) | Test bit 7 of the flags. | ||
| 8DB0 | CALL NZ,CountActiveEnemy | Call CountActiveEnemy if it is set. | ||
| 8DB3 | RES 6,(IX+$10) | Clear bit 6 of the flags. | ||
| 8DB7 | EXX | Switch registers. | ||
| 8DB8 | CALL RunObjectHandler | Run the code for the type of object. | ||
| 8DBB | CALL ApplyCollisionEffects | Deal with any collision at ApplyCollisionEffects. | ||
| 8DBE | POP IX | Restore the address of the slot. | ||
| 8DC0 | LD A,(IX+$00) | Fetch the type of the object. | ||
| 8DC3 | CP $13 | Jump to UpdateEnemies_CheckHit if it is 13. | ||
| 8DC5 | JR Z,UpdateEnemies_CheckHit | |||
| 8DC7 | CP $1C | Jump to UpdateEnemies_Type1C if it is 1C. | ||
| 8DC9 | JR Z,UpdateEnemies_Type1C | |||
| 8DCB | CP $1D | Jump to UpdateEnemies_CheckHit if it is 1D. | ||
| 8DCD | JR Z,UpdateEnemies_CheckHit | |||
| 8DCF | JR UpdateEnemies_Check | Jump to UpdateEnemies_Check. | ||
| UpdateEnemies_Type1C | 8DD1 | LD A,(IX+$14) | Fetch the second state byte of the object. | |
| 8DD4 | CP $02 | Jump to UpdateEnemies_Check if it is two. | ||
| 8DD6 | JR Z,UpdateEnemies_Check | |||
| UpdateEnemies_CheckHit | 8DD8 | LD A,($A1D7) | Fetch the flag from A1D7. | |
| 8DDB | AND A | Test it. | ||
| 8DDC | JR Z,UpdateEnemies_Check | Jump to UpdateEnemies_Check if it is clear. | ||
| 8DDE | LD A,($A1D8) | Fetch the flag from A1D8. | ||
| 8DE1 | AND A | Test it. | ||
| 8DE2 | JR NZ,UpdateEnemies_Check | Jump to UpdateEnemies_Check if it is set. | ||
| 8DE4 | LD (IX+$00),$FF | Otherwise free the slot. | ||
| UpdateEnemies_Check | 8DE8 | BIT 5,(IX+$10) | Jump to UpdateEnemies_Next if bit 5 of the flags is set. | |
| 8DEC | JR NZ,UpdateEnemies_Next | |||
| 8DEE | BIT 3,(IX+$17) | Jump to UpdateEnemies_Next if bit 3 of the second set of flags is set. | ||
| 8DF2 | JR NZ,UpdateEnemies_Next | |||
| 8DF4 | CALL FindHitPosition | Work out the position of a hit. | ||
| 8DF7 | CALL CheckShotCollisions | Check for a collision with a shot. | ||
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This entry point is used by the routine at UpdateEnemies_Skip.
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| UpdateEnemies_Next | 8DFA | LD BC,$0018 | Set the length of a slot. | |
| 8DFD | ADD IX,BC | Move on to the next slot. | ||
| 8DFF | POP BC | Restore the slot counter. | ||
| 8E00 | DEC B | Decrease the slot counter... | ||
| 8E01 | JP NZ,UpdateEnemies_Loop | ...and loop back to UpdateEnemies_Loop until none remain. | ||
| 8E04 | LD A,($8E2B) | Fetch the number of active enemies from 8E2B. | ||
| 8E07 | CP $04 | Return if there are four or more. | ||
| 8E09 | RET NC | Fetch a pseudo-random value from the refresh register. | ||
| 8E0A | LD A,R | Test bit 3. | ||
| 8E0C | AND $08 | |||
| 8E0E | JR Z,UpdateEnemies_Spawn | Jump to UpdateEnemies_Spawn if it is clear. | ||
| 8E10 | LD A,($CE58) | Fetch the map zone from CE58. | ||
| 8E13 | CP $0B | Jump to UpdateEnemies_Spawn if it is 0B or more... | ||
| 8E15 | JR NC,UpdateEnemies_Spawn | |||
| 8E17 | CP $03 | ...or less than 03. | ||
| 8E19 | JR C,UpdateEnemies_Spawn | |||
| 8E1B | JP SpawnSpecialEnemy | Spawn a special enemy. | ||
| UpdateEnemies_Spawn | 8E1E | JP UpdateEnemySpawning_Spawn | Spawn an enemy. | |
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