Chase H.Q.: Routine at AC3C

AC3C: Test for collision with hazard

Input
IX	Address of hazard structure ($A188+)

hazard_hit

AC3C

LD A,(IX+$0F)

IX[15] appears to be a delay of some sort

AC3F

AND A

If IX[15] != 0 then goto hh_ac92

AC40

JR NZ,hh_ac92

AC42

LD A,(IX+$07)

If IX[7] == 0 then return

AC45

AND A

AC46

RET Z

If we arrive here then a hit has occurred.

AC47

LD DE,($A24A)

Load speed

AC4B

JP P,hazard_hit_0

If IX[7] < 0 then DE = 280

AC4E

LD DE,$0118

hazard_hit_0

AC51

LD B,D

BC = DE

AC52

LD C,E

AC53

LD HL,$AD03

Point HL at table_ad03 table

This must be mapping the speed into the 5-entry array.

AC56

LD A,D

A = D top part of speed

AC57

RL E

E ROL 1 double speed

AC59

RLA

A ROL 1

AC5A

AND $03

A &= 3 mask top part to 3 (for ref. turbo speed = $1FF)

AC5C

RR D

RR D halve D to carry?

AC5E

LD D,$00

D = 0

AC60

ADC A,D

A = (A + D + carry) * 2 scale for element size of 2

AC61

ADD A,A

AC62

LD E,A

E = A it's an offset in table_ad03

AC63

ADD HL,DE

HL += DE

AC64

LD A,(HL)

Copy (two bytes?) to IX+17 from table

AC65

LD (IX+$11),A

AC68

INC HL

AC69

LD A,(HL)

AC6A

LD (IX+$12),A

AC6D

SLA C

double BC? adjusted speed retained from earlier

AC6F

RL B

AC71

LD A,B

If B >= 2 BC = 350 so this is if we hit the object very fast it gets put on the left?

AC72

CP $02

AC74

JR C,hazard_hit_1

AC76

LD BC,$015E

hazard_hit_1

AC79

LD (IX+$0D),C

Set bottom byte of horizontal position

AC7C

INC (IX+$07)

Increment IX[7]

AC7F

JR Z,hazard_hit_2

if B is zero then don't store it

AC81

LD (IX+$0E),B

Set top byte of horizontal position

hazard_hit_2

AC84

INC (IX+$01)

Increment IX[1]

AC87

LD BC,$0503

Call start_sfx with BC = $0503

AC8A

CALL start_sfx

AC8D

LD A,$02

A = 2 [set this to 1 and it drives off like a car]

AC8F

LD (IX+$0F),A

Set IX[15] to 2

hh_ac92

AC92

DEC A

A--

AC93

RET Z

If A == 0 return

AC94

LD HL,$ACDB

IX[16] = table_acdb[IX[17]]

AC97

LD C,(IX+$11)

AC9A

LD B,$00

AC9C

ADD HL,BC

AC9D

LD A,(HL)

AC9E

LD (IX+$10),A

ACA1

INC (IX+$11)

Increment IX[17]

ACA4

LD H,(IX+$0E)

Load horizontal position into HL

ACA7

LD L,(IX+$0D)

ACAA

LD D,H

DE = HL

ACAB

LD E,L

ACAC

SRL D

Divide horizontal position by 2?

ACAE

RR E

ACB0

SRL E

Then by 16 once it's 8 bits

ACB2

SRL E

ACB4

SRL E

ACB6

SRL E

ACB8

SBC HL,DE

Then subtract from the previous position

ACBA

LD (IX+$0E),H

Set horizontal position

ACBD

LD (IX+$0D),L

ACC0

LD A,(IX+$13)

Toggle the bottom bit of IX[19]

ACC3

XOR $01

ACC5

LD (IX+$13),A

ACC8

DEC (IX+$12)

Decrement IX[18]

ACCB

RET NZ

If IX[19] != 0 then return

ACCC

XOR A

Zero the horizontal position

ACCD

LD (IX+$0D),A

ACD0

LD (IX+$0E),A

ACD3

INC A

Set IX[19] to 1

ACD4

LD (IX+$13),A

ACD7

LD (IX+$0F),A

Set IX[15] to 1

ACDA

RET

Return

table_acdb

ACDB

DEFB $19,$28,$32,$37,$39,$37,$32,$28

AC94 uses this

ACE3

DEFB $19,$00,$0F,$19,$1F,$22,$24,$22

ACEB

DEFB $1F,$19,$0F,$00,$0A,$10,$13,$15

ACF3

DEFB $13,$10,$0A,$00,$06,$09,$0B,$09

ACFB

DEFB $06,$00,$02,$00,$02,$00,$01,$00

table_ad03

AD03

DEFW $0622

AC53 uses this

AD05

DEFW $0C1C

AD07

DEFW $0E14

AD09

DEFW $120A

AD0B

DEFW $1400