Routines
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CEF8: Step an object through four frames
Used by the routines at CREATURE_UPDATE, WANDERING_MONSTER, SPARKLE_FLY, ANTIBODY_FLIGHT and FIND_WANDER.
Counts bits 0-1 of the graphic round 0-3, leaving the rest: the four frames of a monster's or the creature's walk (WANDERING_MONSTER, CREATURE_UPDATE), the sparkles (SPARKLE_FLY) and others. Knight Lore's next_graphic_no_mod_4 and Alien 8's NEXT_FRAME_MOD4 do the same.
Input
IX the record
NEXT_FRAME_MOD4 CEF8 LD A,(IX+$00)
CEFB LD C,A
CEFC INC A
CEFD AND $03
CEFF LD B,A
CF00 LD A,C
CF01 AND $FC
CF03 OR B
CF04 LD (IX+$00),A
CF07 RET
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