C64 sprite animation routine

C64-sprite-animation.asm

FRAME_COUNT = 10                                ; constant for the nbr of sprite frames you have
.frame_counter !byte .FRAME_COUNT               ; variable to keep track of how far through the animation we are
SPRITE_INITIAL_DATA_POINTER = 128               ; sprite data will be read by VIC-II at 128*64 ($2000)

on_screen_refresh
	dec .frame_counter                      ;  frame_counter variable -= 1
	bne .increment_sprite_pointer           ; if frame_counter > 0, goto .increment_sprite_pointer...
	lda #SPRITE_INITIAL_DATA_POINTER        ; ... otherwise, we should reset to the start of the animation
	sta $07f8                               ; reset the sprite pointer to start of sprite data
	ldx #FRAME_COUNT               
	stx .frame_counter                      ; reset frame_counter to the nbr of sprite frames again
	rts                                     ; return
.increment_sprite_pointer
	inc $07f8                               ; sprite pointer += 1 (moves to the next frame)
	rts                                     ; return