Pentagram: Routine at CBAB

Used by the routine at START.

Once a turn, from the main loop. When DROP_TIMER runs out it stays at 1, so from then on there is a one-in-four chance each turn (two bits of RANDOM). A drop resets the timer (RESET_DROP_TIMER) whether or not it comes to anything, then takes a free one of the two records at FLYERS, copies FLYER_TEMPLATE into it, and gives it a U and a V at random and one of the eight graphics at DROP_GRAPHICS. If the new thing overlaps anything already in the room it is taken away again.

The random U and V are 104 plus a number masked with $2F: 104 to 119 or 136 to 151, never within 8 of the room's middle line. It falls from Z 216.

Used by the routine at START. Once a turn, from the main loop. When DROP_TIMER runs out it stays at 1, so from then on there is a one-in-four chance each turn (two bits of RANDOM). A drop resets the timer (RESET_DROP_TIMER) whether or not it comes to anything, then takes a free one of the two records at FLYERS, copies FLYER_TEMPLATE into it, and gives it a U and a V at random and one of the eight graphics at DROP_GRAPHICS. If the new thing overlaps anything already in the room it is taken away again. The random U and V are 104 plus a number masked with $2F: 104 to 119 or 136 to 151, never within 8 of the room's middle line. It falls from Z 216.
SKY_DROP	CBAB	LD A,(DROP_BAN)	Nothing falls in this room
	CBAE	AND A
	CBAF	RET NZ
	CBB0	LD HL,DROP_TIMER	Count the timer down
	CBB3	DEC (HL)
	CBB4	RET NZ
	CBB5	LD (HL),$01	Then try every turn
	CBB7	LD A,(RANDOM)	One chance in four
	CBBA	AND $03
	CBBC	RET NZ
	CBBD	CALL RESET_DROP_TIMER	The timer starts again
	CBC0	LD HL,FLYERS	The first of the two records, and the template
	CBC3	LD BC,$0020
	CBC6	LD DE,FLYER_TEMPLATE
	CBC9	LD A,(HL)	Both in use: nothing falls
	CBCA	AND A
	CBCB	JR Z,SKY_DROP_0
	CBCD	ADD HL,BC
	CBCE	LD A,(HL)
	CBCF	AND A
	CBD0	RET NZ
SKY_DROP_0	CBD1	EX DE,HL	IX = the free record, filled from the template
	CBD2	PUSH HL
	CBD3	POP IX
	CBD5	LDIR
	CBD7	LD A,(RANDOM)	U at random
	CBDA	AND $2F
	CBDC	ADD A,$68
	CBDE	LD (IX+$01),A
	CBE1	LD A,R	V from the refresh register
	CBE3	AND $2F
	CBE5	ADD A,$68
	CBE7	LD (IX+$02),A
	CBEA	LD A,(RANDOM)	One of the eight graphics, by bits 3-5 of the random number
	CBED	RRA
	CBEE	RRA
	CBEF	RRA
	CBF0	AND $07
	CBF2	LD L,A
	CBF3	LD H,$00
	CBF5	LD DE,DROP_GRAPHICS
	CBF8	ADD HL,DE
	CBF9	LD A,(HL)
	CBFA	LD (IX+$00),A
	CBFD	CALL CALC_PIXEL_XY	Its place on the screen (CALC_PIXEL_XY)
	CC00	CALL DO_ANY_OBJS_INTERSECT	Nothing in the way: it falls (DO_ANY_OBJS_INTERSECT)
	CC03	RET NC	Nothing in the way: it falls (DO_ANY_OBJS_INTERSECT)
	CC04	LD (IX+$00),$00	Something there: no drop after all
	CC08	RET	Something there: no drop after all