Gyruss: Routine at 899E

899E: Handle sprite types $18 - $1C

Used by the routine at handle_sprite_types_0E_11.
handle_sprite_types_18_1C	899E	CP $18	Is sprite type < $18
	89A0	RET C	Then return
	89A1	CP $1A	Is sprite type < $1A
	89A3	JR C,handle_sprite_types_18_1C_1	If so, jump ahead
Sprite types $1A - $1C (circular enemies)
	89A5	LD B,A	B = sprite type
	89A6	LD A,(frame_counter)	Frame counter
	89A9	AND $03	Mod 4
	89AB	JR NZ,handle_sprite_types_18_1C_1	If not zero the skip ahead
	89AD	LD A,B	A = sprite type
	89AE	INC A	A = sprite type + 1
	89AF	CP $1D	Is sprite type + 1 < $1D, i.e. sprite type < $1C, i.e. $1A or $1B
	89B1	JR C,handle_sprite_types_18_1C_0	Then skip next
	89B3	LD A,$1A	Else set sprite type to $1A
handle_sprite_types_18_1C_0	89B5	LD (IX+$00),A	This means rotate between $1A, $1B, and $1C
Sprite types $18 - $19 (three spheres, star shape) plus $1A - 1C
handle_sprite_types_18_1C_1	89B8	BIT 7,(IX+$07)	Text flag bit 7
	89BC	JR Z,L8A2D	If reset, move towards viewer
	89BE	LD A,(sprite_countdown)	Return if countdown
	89C1	OR A	is not zero
	89C2	RET NZ	...
	89C3	LD L,(IX+$06)	Get path address
	89C6	LD H,(IX+$07)	...
	89C9	LD A,(IX+$03)	Get counter
	89CC	SUB $10	Decrement upper nybble
	89CE	LD (IX+$03),A	Save counter
	89D1	JR NC,move_sprite_along_path	If upper nybble >= 0 then jump ahead
	89D3	INC HL	Next path address
	89D4	LD A,(HL)	Get path byte
	89D5	SUB $10	Decrement upper nybble
	89D7	JR C,L8A3C	If < 0 then set flag and return
	89D9	AND $F0	Isolate upper nybble
	89DB	LD B,A	Save it
	89DC	LD A,(IX+$03)	Get counter
	89DF	AND $0F	And apply upper nybble
	89E1	OR B	...
	89E2	LD (IX+$03),A	...
	89E5	LD (IX+$06),L	Set path address
	89E8	LD (IX+$07),H	... (continue into move_sprite_along_path)