Fairlight: Routine at E834

Used by the routine at FILL_NEXT_PIXEL.

Called from FILL_NEXT_PIXEL when the pixel mask wraps round into the byte to the left. The clean copy's pointers for this row and the row above (the low bytes at IY+$7B and IY+$7D) and for the row below, and the screen pointer, all go back a byte; and the texture's two bytes change places, since a texture is 16 pixels wide. Then FILL_WHOLE_BYTE sees whether the new byte can be filled whole. A row's bytes never cross into another row here, because FILL_NEXT_PIXEL stops at column 0.

Used by the routine at FILL_NEXT_PIXEL. Called from FILL_NEXT_PIXEL when the pixel mask wraps round into the byte to the left. The clean copy's pointers for this row and the row above (the low bytes at IY+$7B and IY+$7D) and for the row below, and the screen pointer, all go back a byte; and the texture's two bytes change places, since a texture is 16 pixels wide. Then FILL_WHOLE_BYTE sees whether the new byte can be filled whole. A row's bytes never cross into another row here, because FILL_NEXT_PIXEL stops at column 0.
FILL_BYTE_TO_LEFT	E834	DEC (IY+STEP_AXES-V)	this row and the row above, in the clean copy
	E837	DEC (IY+WORK_RECORD-V)	this row and the row above, in the clean copy
	E83A	EXX	the screen; the texture's other byte for the new screen byte
	E83B	DEC L
	E83C	LD E,C
	E83D	LD C,B
	E83E	LD B,E
	E83F	EXX
	E840	LD HL,(WORK_HEADING)	the row below; then try the byte whole
	E843	DEC L
	E844	LD (WORK_HEADING),HL
	E847	JR FILL_WHOLE_BYTE