Sabre Wulf: Routine at B078

B078: Animate Walk

Used by the routine at UpdatePlayerDirection.

Every other frame, if the player has moved, adds one to the animation frame in bits 0-1 of the sprite ID (wrapping from 03 round to 00).

Input
D	New Y position
E	New X position
IX	Actor record of the player

AnimateWalk

B078

LD A,($5C78)

Fetch the low byte of FRAMES.

B07B

AND %00000001

Keep only bit 0.

B07D

RET NZ

Return if this is an odd frame.

B07E

LD A,D

Fetch the new Y position.

B07F

XOR (IX+$04)

Find the difference from the Y position of the player.

B082

LD C,A

Stash the Y difference in C.

B083

LD A,E

Fetch the new X position.

B084

XOR (IX+$03)

Find the difference from the X position of the player.

B087

OR C

Return if the player has not moved.

B088

RET Z

B089

LD A,(IX+$00)

Fetch the sprite ID of the player.

B08C

LD C,A

Stash the sprite ID in C.

B08D

INC A

Move on to the next frame of animation.

B08E

AND %00000011

Keep only bits 0-1.

B090

LD B,A

Stash the new frame in B.

B091

LD A,C

Fetch the old sprite ID.

B092

AND %11111100

Keep only bits 2-7.

B094

OR B

Merge in the new frame.

B095

LD (IX+$00),A

Set the new sprite ID of the player.

B098

RET

Return.