Gyruss: Routine at 900E

900E: Create shot from mine

Used by the routines at create_mines and display_mines.
create_shot_from_mine	900E	LD HL,mine_countdown_to_shoot	Decrement countdown
	9011	DEC (HL)	...
	9012	RET NZ	Return if not 0
	9013	LD IY,mines_background_data	Mine data
	9017	LD A,(IY+$04)	Check if mine exists
	901A	OR (IY+$05)	...
	901D	JR Z,create_shot_from_mine_0	Skip ahead if not
	901F	LD HL,active_enemy_shots	Increment enemy shots
	9022	INC (HL)	...
	9023	RST $28	Allocate sprite
	9024	LD (IX+$00),$12	Missile
	9028	LD (IX+$0B),$0A	Set color
	902C	LD A,(IY+$07)	Set polar y to mine polar y
	902F	LD (IX+$01),A	...
	9032	LD A,(IY+$08)	Set polar x to mine polar x
	9035	LD (IX+$02),A	...
	9038	RST $30	Load sprite pattern
create_shot_from_mine_0	9039	CALL stage_data_addr	Get stage data address in IY
	903C	RST $20	Random number
	903D	AND $3F	0-63
	903F	ADD A,(IY+$06)	Add ?
	9042	LD (mine_countdown_to_shoot),A	Set countdown to random value
	9045	RET