Atic Atac: Routine at 9731

Used by the routine at TRAPDOOR_CLOSED.

Reached only from the trapdoor's handler, TRAPDOOR, and only while the player is standing on it -- PLAYER_AT_DOOR with a tolerance of $1818. It draws room $96, which is not a room but the trapdoor fall's twelve nested rectangles (see the room types), then runs 128 times: each pass beeps a note whose pitch comes from the frame counter at $5C78 and walks down as the loop counts up, picks black or white from bit 3 of it, writes that into two cells of the attribute file and floods the rest outwards with SPIRAL_FILL. It ends in ENTER_ROOM, which takes the player to the trapdoor's other half -- the landing in the room below.

Never reached in any of the recorded playthroughs, which is why the code map left it as data until it was disassembled by hand.

Used by the routine at TRAPDOOR_CLOSED. Reached only from the trapdoor's handler, TRAPDOOR, and only while the player is standing on it -- PLAYER_AT_DOOR with a tolerance of $1818. It draws room $96, which is not a room but the trapdoor fall's twelve nested rectangles (see the room types), then runs 128 times: each pass beeps a note whose pitch comes from the frame counter at $5C78 and walks down as the loop counts up, picks black or white from bit 3 of it, writes that into two cells of the attribute file and floods the rest outwards with SPIRAL_FILL. It ends in ENTER_ROOM, which takes the player to the trapdoor's other half -- the landing in the room below. Never reached in any of the recorded playthroughs, which is why the code map left it as data until it was disassembled by hand.
TRAPDOOR_FALL	9731	LD BC,$1818
	9734	CALL PLAYER_AT_DOOR
	9737	JP NC,DRAW_DOOR
	973A	CALL CLEAR_PLAY_AREA
	973D	LD A,$96
	973F	PUSH IX
	9741	CALL DRAW_ROOM_A
	9744	POP IX
	9746	LD B,$80
TRAPDOOR_FALL_0	9748	LD A,($5C78)	The frame counter, so the pitch follows real time rather than a count of its own.
	974B	LD C,A
TRAPDOOR_FALL_1	974C	PUSH BC
	974D	LD A,B
	974E	CPL
	974F	LD B,A
	9750	CALL BEEP	One cycle of BEEP with B complemented, which is what walks the pitch down as the loop counts up.
	9753	POP BC
	9754	LD A,($5C78)
	9757	CP C
	9758	JR Z,TRAPDOOR_FALL_1
	975A	AND $07	Low three bits of the counter all clear -- one frame in eight -- gives $47, white; otherwise $00, black.
	975C	LD A,$00
	975E	JR NZ,TRAPDOOR_FALL_2
	9760	LD A,$47
TRAPDOOR_FALL_2	9762	LD L,A
	9763	LD H,A
	9764	LD ($596B),HL
	9767	LD ($598B),HL
	976A	PUSH BC
	976B	CALL SPIRAL_FILL	Flood the change outwards from the middle.
	976E	POP BC
	976F	DJNZ TRAPDOOR_FALL_0
	9771	JP ENTER_ROOM	Straight back into the main loop; there is no return.
SPIRAL_FILL	9774	LD BC,$170B
	9777	LD HL,$5AE0	$5AE0 is the last row of the attribute file; the spiral is walked backwards from there.
	977A	LD DE,$0020
TRAPDOOR_FALL_3	977D	PUSH HL
	977E	AND A
	977F	SBC HL,DE
	9781	INC L
	9782	LD A,(HL)
	9783	POP HL
	9784	PUSH BC
TRAPDOOR_FALL_4	9785	LD (HL),A
	9786	INC L
	9787	DJNZ TRAPDOOR_FALL_4
	9789	POP BC
	978A	PUSH BC
TRAPDOOR_FALL_5	978B	LD (HL),A
	978C	AND A
	978D	SBC HL,DE
	978F	DJNZ TRAPDOOR_FALL_5
	9791	POP BC
	9792	PUSH BC
TRAPDOOR_FALL_6	9793	LD (HL),A
	9794	DEC L
	9795	DJNZ TRAPDOOR_FALL_6
	9797	POP BC
	9798	PUSH BC
TRAPDOOR_FALL_7	9799	LD (HL),A
	979A	ADD HL,DE
	979B	DJNZ TRAPDOOR_FALL_7
	979D	LD (HL),A
	979E	AND A
	979F	SBC HL,DE
	97A1	INC L
	97A2	POP BC
	97A3	DEC B	Two rows and one column shorter each time round.
	97A4	DEC B
	97A5	DEC C
	97A6	JR NZ,TRAPDOOR_FALL_3
	97A8	RET