Routines
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B0D1: Test Target Range
Return carry if this actor is close enough to its target: Jetman when he is riding the rover, otherwise the parked rover. The world X difference is scaled by 08 and must be less than 00C0 and the target must be 00-1F below the actor.
Input
IX Actor slot
Handler_Missile_TestJetmanRange B0D1 LD A,($6078) Fetch Jetman_Slot.
Types 12-19 are Jetman seated on the rover; use his slot. Otherwise use the rover slot when its type is in 1A-29.
B0D4 SUB $12 Subtract 12.
B0D6 CP $08 Jump to Handler_Missile_FetchJetman if Jetman is seated.
B0D8 JR C,Handler_Missile_FetchJetman
B0DA LD A,($6090) Fetch Rover_Slot.
B0DD SUB $1A Subtract 1A.
B0DF CP $10 Jump to Handler_Missile_OutOfRange if that is not a rover frame.
B0E1 JR NC,Handler_Missile_OutOfRange
B0E3 LD HL,($6092) Fetch Rover_Position.
B0E6 LD A,($6094) Fetch the rover Y.
B0E9 LD C,A Stash it in C.
Scale both world X values and test the horizontal range.
Handler_Missile_ScaleTargetX B0EA ADD HL,HL Multiply the target world X by 08.
B0EB ADD HL,HL
B0EC ADD HL,HL
B0ED LD E,(IX+$02) Fetch the actor world X.
B0F0 LD D,(IX+$03) Fetch the high byte.
B0F3 EX DE,HL Switch the pairs.
B0F4 ADD HL,HL Multiply the actor world X by 08.
B0F5 ADD HL,HL
B0F6 ADD HL,HL
Take the absolute horizontal distance between the two scaled X values.
B0F7 AND A Clear the carry flag.
B0F8 SBC HL,DE Subtract the target world X.
B0FA LD A,H Fetch the high byte of the difference.
B0FB AND A Jump to Handler_Missile_SubtractRange if the result is positive.
B0FC JP P,Handler_Missile_SubtractRange
B0FF CALL NegatePair Call NegatePair.
Return unless the actor is within the horizontal range.
Handler_Missile_SubtractRange B102 LD DE,$00C0 DE=00C0.
B105 AND A Clear the carry flag.
B106 SBC HL,DE Subtract the range.
B108 RET NC Return if the actor is too far away.
Test the vertical distance to the target.
B109 LD A,(IX+$04) Fetch the actor Y.
B10C SUB C Subtract the target Y.
B10D NEG Negate the difference.
B10F CP $20 Compare it against 20.
B111 RET Return.
Use Jetman's position as the target when he is seated.
Handler_Missile_FetchJetman B112 LD HL,($607A) Fetch Jetman_Position.
B115 LD A,($607C) Fetch Jetman_Y.
B118 LD C,A Stash it in C.
B119 JR Handler_Missile_ScaleTargetX Jump to Handler_Missile_ScaleTargetX.
Handler_Missile_OutOfRange B11B AND A Return with the carry flag clear.
B11C RET
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