Nightshade: Routine at D978

D978: Set a villain's or a monster's picture for its facing

Used by the routines at MONSTER112_UPDATE and VILLAIN_WANDER.

A villain has two pictures, one for facing +V or -U and one for +U or -V (bit 1 of its graphic), and each is mirrored for the U facings (bit 6 of +7, from the facing's bit 6); bit 0 is toggled every turn, the walking frame. With the town turned round (VIEW) bit 1 is flipped, since the knight then sees the villain's other side. Used for the monsters of graphics 112-127 too (MONSTER112_UPDATE).

Input
IX	The record

FACING_PICTURE

D978

LD A,(VIEW)

B: 2 if the town is turned round

D97B

ADD A,A

D97C

LD B,A

D97D

LD A,(IX+$06)

C: 2 for facing +V or -U, 0 for +U or -V

D980

SUB $40

D982

RLCA

D983

RLCA

D984

AND $02

D986

LD C,A

D987

LD A,(IX+$00)

Bit 1 of the graphic from C, flipped by the view; bit 0 toggled

D98A

AND $FD

D98C

OR C

D98D

XOR $01

D98F

XOR B

D990

LD (IX+$00),A

D993

LD A,(IX+$06)

Mirrored when facing along U

D996

AND $40

D998

LD C,A

D999

LD A,(IX+$07)

D99C

AND $BF

D99E

OR C

D99F

LD (IX+$07),A

D9A2

RET