Routines
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8E2D: Apply Collision Effects
Used by the routine at UpdateEnemies.
Works out what happens when the player's ship hits an object. The object sets the byte at 8E2C when it is updated, and each bit of that byte selects an effect:
Bit Effect
7 Slow the ship down (SlowShip)
6 Damage the ship (DamageShip)
5 Drain fuel (DrainFuel)
4 Bounce the ship (BounceShip)
3 Mark the object as destroyed (DestroyObject)
2 Add fuel (AddFuel)
1 Add a ship (AddShip)
0 Mark the object as hit (MarkObjectHit)
Input
IX Address of the object
ApplyCollisionEffects 8E2D LD A,($96AB) Fetch the flag from 96AB.
8E30 AND A Test it.
8E31 RET NZ Return if it is set.
8E32 LD A,($8F53) Fetch the explosion counter from 8F53.
8E35 AND A Test it.
8E36 RET NZ Return if the ship is exploding.
8E37 LD A,($8E2C) Fetch the collision effects from 8E2C.
8E3A AND A Test them.
8E3B RET Z Return if there are none.
8E3C LD A,($A1D8) Fetch the collision flag from A1D8.
8E3F AND A Test it.
8E40 RET Z Return if there is no collision.
8E41 LD IX,($AD46) Fetch the address of the object that was hit from CurrentObject.
8E45 BIT 3,(IX+$17) Test bit 3 of its second set of flags.
8E49 RET NZ Return if it is set.
8E4A LD L,(IX+$11) Fetch the screen position of the object into HL.
8E4D LD H,(IX+$12)
8E50 LD IX,$ABA4 Use the hit data at CollisionBox.
8E54 LD (IX+$03),A Store the collision effects in the hit data.
8E57 LD A,L Fetch the horizontal screen position.
8E58 CP $8E Is it 8E or more?
8E5A RET NC Return if so.
8E5B CP $28 Is it lower than 28?
8E5D RET C Return if so.
8E5E LD (IX+$00),L Store the screen position in the hit data.
8E61 LD (IX+$01),H
8E64 LD A,($5C29) Fetch the value from 5C29.
8E67 LD (IX+$02),A Store it in the hit data.
8E6A LD A,($5C38) Fetch the value from ShipRow.
8E6D ADD A,$08 Add eight.
8E6F LD H,A Use it as the vertical position.
8E70 LD L,$64 Set the horizontal position to 64.
8E72 LD D,$28 Set the width to 28...
8E74 LD E,$10 ...and the height to 10.
8E76 CALL TestBoxesOverlap Check for a hit.
8E79 LD IX,($AD46) Bring IX back from CurrentObject.
8E7D LD IY,$C8E5 Use the player's object.
8E81 LD A,($5C1C) Fetch the value from ScratchValue.
8E84 AND A Test it.
8E85 JP Z,ApplyPlayerCollision Jump to ApplyPlayerCollision if it is zero.
8E88 LD A,$80 Set CollisionKind to 80.
8E8A LD ($D0BC),A
8E8D LD A,($8E2C) Fetch the collision effects from 8E2C.
8E90 LD C,A Copy them into C.
8E91 INC A Increment them.
8E92 JR NZ,ApplyCollisionEffects_Bit7 Jump to ApplyCollisionEffects_Bit7 if they were not FF.
8E94 DEC A Make 896F FF.
8E95 LD ($896F),A
8E98 SET 4,(IX+$10) Set bit 4 of the flags of the object.
8E9C JP PlayHitSound Play the explosion sound.
ApplyCollisionEffects_Bit7 8E9F BIT 7,C Test bit 7.
8EA1 CALL NZ,SlowShip Slow the ship down if it is set.
8EA4 BIT 6,C Test bit 6.
8EA6 CALL NZ,DamageShip Damage the ship if it is set.
8EA9 BIT 5,C Test bit 5.
8EAB CALL NZ,DrainFuel Drain the fuel if it is set.
8EAE BIT 4,C Test bit 4.
8EB0 CALL NZ,BounceShip Bounce the ship if it is set.
8EB3 BIT 3,C Test bit 3.
8EB5 CALL NZ,DestroyObject Mark the object as destroyed if it is set.
8EB8 BIT 2,C Test bit 2.
8EBA CALL NZ,AddFuel Add fuel if it is set.
8EBD PUSH BC Save the effects.
8EBE BIT 1,C Test bit 1.
8EC0 CALL NZ,AddShip Add a ship if it is set.
8EC3 POP BC Restore the effects.
8EC4 BIT 0,C Jump to MarkObjectHit if bit 0 is set.
8EC6 JP NZ,MarkObjectHit
8EC9 RET Return.
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