Ant Attack: Routine at 8300

8300: Clear every fourth row of the render buffer

Used by the routine at DRAW_VIEW. Unrolled: 29 rows of 32 bytes, four rows apart, from row 12 of the render buffer. CLEAR_PHASE moves the starting row on each call, so DRAW_VIEW's four calls clear rows 12-127 -- the rows COPY_TO_SCREEN copies to the screen.
CLEAR_BUFFER_ROWS	8300	LD DE,$0061	The step to four rows on, the render buffer, 29 rows of zeros.
	8303	LD H,$A1
	8305	LD BC,$1D00
	8308	LD A,(CLEAR_PHASE)	Next quarter: rows 12, 13, 14 or 15 to start from.
	830B	ADD A,$20
	830D	AND $60
	830F	LD (CLEAR_PHASE),A
	8312	ADD A,$80
	8314	LD L,A
CLEAR_BUFFER_ROWS_0	8315	LD (HL),C	32 bytes.
	8316	INC L
	8317	LD (HL),C
	8318	INC L
	8319	LD (HL),C
	831A	INC L
	831B	LD (HL),C
	831C	INC L
	831D	LD (HL),C
	831E	INC L
	831F	LD (HL),C
	8320	INC L
	8321	LD (HL),C
	8322	INC L
	8323	LD (HL),C
	8324	INC L
	8325	LD (HL),C
	8326	INC L
	8327	LD (HL),C
	8328	INC L
	8329	LD (HL),C
	832A	INC L
	832B	LD (HL),C
	832C	INC L
	832D	LD (HL),C
	832E	INC L
	832F	LD (HL),C
	8330	INC L
	8331	LD (HL),C
	8332	INC L
	8333	LD (HL),C
	8334	INC L
	8335	LD (HL),C
	8336	INC L
	8337	LD (HL),C
	8338	INC L
	8339	LD (HL),C
	833A	INC L
	833B	LD (HL),C
	833C	INC L
	833D	LD (HL),C
	833E	INC L
	833F	LD (HL),C
	8340	INC L
	8341	LD (HL),C
	8342	INC L
	8343	LD (HL),C
	8344	INC L
	8345	LD (HL),C
	8346	INC L
	8347	LD (HL),C
	8348	INC L
	8349	LD (HL),C
	834A	INC L
	834B	LD (HL),C
	834C	INC L
	834D	LD (HL),C
	834E	INC L
	834F	LD (HL),C
	8350	INC L
	8351	LD (HL),C
	8352	INC L
	8353	LD (HL),C
	8354	ADD HL,DE	Four rows on.
	8355	DJNZ CLEAR_BUFFER_ROWS_0	Four rows on.
	8357	RET