Splitting Images: Routine at 60473

60473: Colourise Preview Grid

Used by the routines at Game_Loop, Game_Initialisation and LevelComplete.
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	60473	LD B,4	Set a counter in B for 4 rows.
	60475	LD DE,22678	DE=22678 (attribute buffer location).
	60478	LD HL,60591	HL=AttributeData_PreviewGrid.
PreviewGrid_RowCounter_Loop	60481	PUSH BC	Stash the row counter on the stack.
	60482	LD B,2	Set a counter in B for 2 character blocks per square.
PreviewGrid_BlockCounter_Loop	60484	PUSH BC	Stash the block counter and the attribute reference pointer on the stack.
	60485	PUSH HL
	60486	LD BC,10	Copy 0010 bytes from HL to DE.
	60489	LDIR	Copy 0010 bytes from HL to DE.
	60491	LD HL,22	DE+=0022.
	60494	ADD HL,DE
	60495	EX DE,HL
	60496	POP HL	Restore the attribute reference pointer and the block counter from the stack.
	60497	POP BC
	60498	DJNZ PreviewGrid_BlockCounter_Loop	Decrease block counter by one and loop back to PreviewGrid_BlockCounter_Loop until the block counter is zero.
	60500	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 10 bytes - the data is actually 16 bytes long, to cope with this reference movement.
	60501	INC HL	Increment the attribute reference pointer by two.
	60502	INC HL	Increment the attribute reference pointer by two.
	60503	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.
	60505	RET	Return.