Alien (BUGFIX 1.7): Routine at 34967

Animates marker channel A — the walking crew figure that marks the viewed room on the deck map (placed by PlaceRoomMarkerA). Skips if bit 7 of the animation-freeze flag at 31263 is set.

Decrements the frame counter at 33739; when it reaches zero, resets the counter to 10 and XOR-blits two consecutive 3×12-byte sprite frames from the animation table at 26853 (indexed by the frame phase in 31263 bits 0-1) onto the display at the address stored in SprDestA.

Calling this routine twice per frame (once to erase, once to draw the next frame) produces flicker-free sprite animation via double-buffered XOR.

Used by the routines at 36457, 39718 and 43242.

Animates marker channel A — the walking crew figure that marks the viewed room on the deck map (placed by PlaceRoomMarkerA). Skips if bit 7 of the animation-freeze flag at 31263 is set. Decrements the frame counter at 33739; when it reaches zero, resets the counter to 10 and XOR-blits two consecutive 3×12-byte sprite frames from the animation table at 26853 (indexed by the frame phase in 31263 bits 0-1) onto the display at the address stored in SprDestA. Calling this routine twice per frame (once to erase, once to draw the next frame) produces flicker-free sprite animation via double-buffered XOR. Used by the routines at 36457, 39718 and 43242.
34967	LD A,(31263)	A = animation-freeze / frame-phase byte (31263)
34970	BIT 7,A	bit 7 = freeze flag
34972	RET NZ	frozen: skip animation this frame
34973	LD HL,33691	HL = frame counter A (33739)
34976	DEC (HL)	tick down counter
34977	RET NZ	not expired: nothing to do
34978	LD (HL),10	reset counter to 10 frames per phase
34980	LD B,2	draw 2 sprite rows
This entry point is used by the routines at 35101 and 43242.
34982	PUSH BC	save row counter
34983	LD E,A	E = frame phase (0-3)
34984	LD D,0
34986	LD HL,26853	HL = base of crew-A animation table (26853)
34989	ADD HL,DE	index by phase × 2
34990	ADD HL,DE
34991	LD A,(HL)	read 16-bit sprite bitmap pointer
34992	INC HL
34993	LD H,(HL)
34994	LD L,A	HL = pointer to 3-byte sprite row data
34995	EX DE,HL	DE = sprite data source
34996	LD HL,(33686)	HL = screen destination address (33686)
34999	CALL 35065	XOR-blit 3 bytes × 12 rows onto screen
35002	POP BC	restore row counter
35003	DEC B
35004	RET Z	done after 2 rows
35005	LD A,(31263)	advance to next frame phase
35008	INC A
35009	AND 3	wrap phase 0-3
35011	LD (31263),A	store updated phase
35014	JR 34982	blit second sprite row