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Routines |
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Handles the nastie types which chase the player: the bat (sprite IDs 68 to 6B), the lizard (74 to 77) and the snake (78 to 7B). Every time they are handled the velocity of the nastie is changed by 08 towards the position of the player, up to a maximum of 30 in each direction (see LimitVelocity).
The nastie bounces off the edges of the screen, is stopped by objects in the room, and is blown up (by BlowUpActor) if it touches the player or if the player is not alive.
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Count off the nastie if it is not in the same room as the player.
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| HandlerChasingNastie | A4D7 | LD A,($9703) | Fetch the room of the player from 9703. | |||||
| A4DA | CP (IX+$01) | Jump to ExpireActor if the nastie is in a different room to the player. | ||||||
| A4DD | JR NZ,ExpireActor | |||||||
| A4DF | LD A,$17 | Set the width of the nastie in Actor_Width to 17. | ||||||
| A4E1 | LD ($96AD),A | |||||||
| A4E4 | CALL StoreEntity | Remember the previous position of the nastie. | ||||||
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Blow up the nastie if the player is not alive.
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| A4E7 | LD A,($9702) | Fetch the sprite ID of the player from ImmortalData. | ||||||
| A4EA | SUB $10 | Subtract 10 (the first Sabreman sprite ID). | ||||||
| A4EC | CP $20 | Jump to BlowUpActor to blow up the nastie if the player is not alive. | ||||||
| A4EE | JR NC,BlowUpActor | |||||||
| A4F0 | LD BC,$3008 | Set the maximum velocity in B to 30 and the amount to change the velocity by in C to 08. | ||||||
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Change the X velocity towards the player.
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| A4F3 | LD A,($9705) | Fetch the X position of the player from 9705. | ||||||
| A4F6 | SUB (IX+$03) | Subtract the X position of the nastie. | ||||||
| A4F9 | JR Z,HandlerChasingNastie_StoreX | Jump to HandlerChasingNastie_StoreX if the positions are the same, with a velocity of zero. | ||||||
| A4FB | LD A,C | Fetch the amount to change the velocity by. | ||||||
| A4FC | JR NC,HandlerChasingNastie_AddX | Jump to HandlerChasingNastie_AddX if the player is to the right of the nastie. | ||||||
| A4FE | NEG | Negate the amount to change the velocity by. | ||||||
| HandlerChasingNastie_AddX | A500 | ADD A,(IX+$06) | Add the X velocity of the nastie. | |||||
| A503 | CALL LimitVelocity | Limit the X velocity. | ||||||
| HandlerChasingNastie_StoreX | A506 | LD (IX+$06),A | Set the X velocity of the nastie. | |||||
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Change the Y velocity towards the player.
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| A509 | LD A,($9706) | Fetch the Y position of the player from 9706. | ||||||
| A50C | CP (IX+$04) | Compare with the Y position of the nastie. | ||||||
| A50F | JR Z,HandlerChasingNastie_StoreY | Jump to HandlerChasingNastie_StoreY if the positions are the same (A still holds the Y position of the player at this point, and this is what is used as the Y velocity). | ||||||
| A511 | LD A,C | Fetch the amount to change the velocity by. | ||||||
| A512 | JR NC,HandlerChasingNastie_AddY | Jump to HandlerChasingNastie_AddY if the player is below the nastie. | ||||||
| A514 | NEG | Negate the amount to change the velocity by. | ||||||
| HandlerChasingNastie_AddY | A516 | ADD A,(IX+$07) | Add the Y velocity of the nastie. | |||||
| A519 | CALL LimitVelocity | Limit the Y velocity. | ||||||
| HandlerChasingNastie_StoreY | A51C | LD (IX+$07),A | Set the Y velocity of the nastie. | |||||
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Move the nastie, bouncing it off the edges of the screen.
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| A51F | CALL FaceDirection | Make the nastie face the way it is moving. | ||||||
| A522 | CALL CalculateNewPosition | Work out the new position of the nastie. | ||||||
| A525 | BIT 0,B | Jump to BounceNastieHorizontally if the nastie has hit the left or right edge of the screen. | ||||||
| A527 | JR NZ,BounceNastieHorizontally | |||||||
| A529 | BIT 1,B | Jump to BounceNastieVertically if the nastie has hit the top or bottom edge of the screen. | ||||||
| A52B | JR NZ,BounceNastieVertically | |||||||
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This entry point is used by the routines at BounceNastieHorizontally and BounceNastieVertically.
Stop the nastie moving through objects in the room.
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| HandlerChasingNastie_Move | A52D | LD BC,$1717 | Set the height and width of the nastie in B and C to 17. | |||||
| A530 | CALL SlideActorPastObjects | Stop the nastie passing through objects in the room. | ||||||
| A533 | LD (IX+$03),E | Set the X position of the nastie. | ||||||
| A536 | LD (IX+$04),D | Set the Y position of the nastie. | ||||||
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Blow up the nastie if it touches the player, otherwise draw it.
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| A539 | LD BC,$1313 | Set the reach used to test whether the nastie is touching the player in BC to 1313. | ||||||
| A53C | CALL TestActorHurtingPlayer | Test whether the nastie is touching the player. | ||||||
| A53F | JP NC,DisplayActor | Jump to DisplayActor to display the nastie if it is not touching the player. | ||||||
| A542 | JP BlowUpActor | Jump to BlowUpActor to blow up the nastie. | ||||||
| Prev: A4C3 | Up: Map | Next: A545 |