Splitting Images: Routine at EC39

EC39: Colourise Preview Grid

Used by the routines at Game_Loop, Game_Initialisation and D894.
Colours in the green checkerboard attribute pattern. Note, it doesn't alter the top row at all - only the rows which will have content in them.
Colourise_PreviewGrid	EC39	LD B,$04	Set a counter in B for 04 rows.
	EC3B	LD DE,$5896	DE=5896 (attribute buffer location).
	EC3E	LD HL,$ECAF	HL=AttributeData_PreviewGrid.
PreviewGrid_RowCounter_Loop	EC41	PUSH BC	Stash the row counter on the stack.
	EC42	LD B,$02	Set a counter in B for 02 character blocks per square.
PreviewGrid_BlockCounter_Loop	EC44	PUSH BC	Stash the block counter and the attribute reference pointer on the stack.
	EC45	PUSH HL
	EC46	LD BC,$000A	Copy 000A bytes from HL to DE.
	EC49	LDIR	Copy 000A bytes from HL to DE.
	EC4B	LD HL,$0016	DE+=0016.
	EC4E	ADD HL,DE
	EC4F	EX DE,HL
	EC50	POP HL	Restore the attribute reference pointer and the block counter from the stack.
	EC51	POP BC
	EC52	DJNZ PreviewGrid_BlockCounter_Loop	Decrease block counter by one and loop back to PreviewGrid_BlockCounter_Loop until the block counter is zero.
	EC54	POP BC	Restore the row counter from the stack.
This is how it becomes checkered, we move the pointer forward by two (each block is two character blocks wide) and then it can alternate between the two attribute values. Although we copy 0A bytes - the data is actually 10 bytes long, to cope with this reference movement.
	EC55	INC HL	Increment the attribute reference pointer by two.
	EC56	INC HL	Increment the attribute reference pointer by two.
	EC57	DJNZ PreviewGrid_RowCounter_Loop	Decrease the row counter by one and loop back to PreviewGrid_RowCounter_Loop until all the rows have been coloured in.
	EC59	RET	Return.