Everyone's a Wally: Routine at B931

B931: Clear Banner

Used by the routine at PrintBanner.
Clear_Banner	B931	PUSH HL	Stash HL, BC and DE on the stack.
	B932	PUSH BC
	B933	PUSH DE
	B934	LD IX,$81F8	IX=ScreenBuffer_Locations.
We're not clearing the whole screen buffer, just 20 rows.
	B938	LD C,$20	C=20 (row counter).
Fetch the screen buffer location.
Clear_Banner_Vertical_Loop	B93A	LD L,(IX+$00)	L=*IX+00.
	B93D	LD H,(IX+$01)	H=*IX+01.
Clear the current row.
	B940	LD B,$20	B=20 (column counter).
Clear_Banner_Horizontal_Loop	B942	LD (HL),$00	Write 00 to HL.
	B944	INC HL	Increment HL by one.
	B945	DJNZ Clear_Banner_Horizontal_Loop	Decrease column counter by one and loop back to Clear_Banner_Horizontal_Loop until counter is zero.
Move onto the next screen buffer location.
	B947	INC IX	Increment IX by two.
	B949	INC IX	Increment IX by two.
	B94B	DEC C	Decrease the row counter held in C by one.
	B94C	JR NZ,Clear_Banner_Vertical_Loop	Jump to Clear_Banner_Vertical_Loop until C is zero.
	B94E	JP StackRestore	Jump to StackRestore.