Gunfright: Routine at BC37

BC37: Choose Outlaw Move

Used by the routine at HandleWaitingOutlaw.

Gives the waiting outlaw a new move: a speed in each direction of up to three, taken from random numbers, and a time for the move of eight to thirty nine frames. On the last move the speeds are doubled.

Input
IX	The address of the outlaw

Choose a horizontal speed.

ChooseOutlawMove

BC37

LD A,($A218)

Fetch a random number and keep it in C.

BC3A

LD C,A

BC3B

AND %00000011

Keep a number from 00 to 03.

BC3D

BIT 7,C

Jump to ChooseOutlawMove_Vertical if the top bit of the random number is clear.

BC3F

JR Z,ChooseOutlawMove_Vertical

BC41

NEG

Make the speed negative.

Store it, then choose a vertical speed.

ChooseOutlawMove_Vertical

BC43

LD (IX+$01),A

Set the horizontal speed.

BC46

LD A,($A219)

Fetch another random number and keep it in C.

BC49

LD C,A

BC4A

AND %00000011

Keep a number from 00 to 03.

BC4C

BIT 7,C

Jump to ChooseOutlawMove_Time if the top bit of the random number is clear.

BC4E

JR Z,ChooseOutlawMove_Time

BC50

NEG

Make the speed negative.

Store the vertical speed, then set the time of the move.

ChooseOutlawMove_Time

BC52

LD (IX+$03),A

Set the vertical speed.

BC55

LD A,($A216)

Fetch the frame counter.

BC58

AND %00011111

Keep a number from 00 to 1F.

BC5A

ADD A,$08

Add eight.

BC5C

LD (IX+$0B),A

Set the timer for the move.

BC5F

DEC (IX+$0A)

Count down the moves left.

BC62

RET NZ

Return unless that was the last move.

BC63

SLA (IX+$01)

Double the horizontal speed.

BC67

SLA (IX+$03)

Double the vertical speed.

BC6B

RET

Return.