Atic Atac: Routine at 9774

Used by the routine at FallThroughTrapdoor.

Moves the colours of a set of 0B rings of the attribute buffer outwards. Each ring is a square with sides of 17 cells, starting from the bottom left of the screen (5AE0) and moving one cell up and one to the right for each ring, so that the sides are 02 cells shorter. All of the cells of a ring are given the colour of the cell diagonally inside the first one.

Used by the routine at FallThroughTrapdoor. Moves the colours of a set of 0B rings of the attribute buffer outwards. Each ring is a square with sides of 17 cells, starting from the bottom left of the screen (5AE0) and moving one cell up and one to the right for each ring, so that the sides are 02 cells shorter. All of the cells of a ring are given the colour of the cell diagonally inside the first one.
RippleAttributes	9774	LD BC,$170B	BC=170B (B is the length of the sides and C is the number of rings).
	9777	LD HL,$5AE0	HL=5AE0 (the start of the first ring).
	977A	LD DE,$0020	DE=0020 (the size of a row).
RippleAttributes_Ring	977D	PUSH HL	Stash HL on the stack.
	977E	AND A	Move up one row.
	977F	SBC HL,DE	Move up one row.
	9781	INC L	Move one cell to the right.
	9782	LD A,(HL)	Fetch the attribute of that cell.
	9783	POP HL	Restore HL from the stack.
	9784	PUSH BC	Stash the length on the stack.
Draw the bottom of the ring, from left to right.
RippleAttributes_Bottom	9785	LD (HL),A	Write A to the attribute buffer.
	9786	INC L	Move one cell to the right.
	9787	DJNZ RippleAttributes_Bottom	Decrease the length by one and loop back to RippleAttributes_Bottom until it is zero.
	9789	POP BC	Restore the length from the stack.
	978A	PUSH BC	Stash it on the stack again.
Draw the right side of the ring, from bottom to top.
RippleAttributes_Right	978B	LD (HL),A	Write A to the attribute buffer.
	978C	AND A	Move up one row.
	978D	SBC HL,DE	Move up one row.
	978F	DJNZ RippleAttributes_Right	Decrease the length by one and loop back to RippleAttributes_Right until it is zero.
	9791	POP BC	Restore the length from the stack.
	9792	PUSH BC	Stash it on the stack again.
Draw the top of the ring, from right to left.
RippleAttributes_Top	9793	LD (HL),A	Write A to the attribute buffer.
	9794	DEC L	Move one cell to the left.
	9795	DJNZ RippleAttributes_Top	Decrease the length by one and loop back to RippleAttributes_Top until it is zero.
	9797	POP BC	Restore the length from the stack.
	9798	PUSH BC	Stash it on the stack again.
Draw the left side of the ring, from top to bottom.
RippleAttributes_Left	9799	LD (HL),A	Write A to the attribute buffer.
	979A	ADD HL,DE	Move down one row.
	979B	DJNZ RippleAttributes_Left	Decrease the length by one and loop back to RippleAttributes_Left until it is zero.
Move on to the next ring, which is inside this one.
	979D	LD (HL),A	Write A to the attribute buffer.
	979E	AND A	Move up one row.
	979F	SBC HL,DE	Move up one row.
	97A1	INC L	Move one cell to the right.
	97A2	POP BC	Restore the length from the stack.
	97A3	DEC B	Make the sides two cells shorter.
	97A4	DEC B	Make the sides two cells shorter.
	97A5	DEC C	Decrease the number of rings by one and loop back to RippleAttributes_Ring until it is zero.
	97A6	JR NZ,RippleAttributes_Ring
	97A8	RET	Return.