Used by the routines at BLIT_SPRITE_MIRRORED, DRAW_TURNED_RIGHT, DRAW_FLIP_ANTIDIAGONAL, BLIT_SPRITE_FLIPPED, DRAW_FLIP_DIAGONAL, COLOURS_MIRRORED, COLOURS_TURNED_RIGHT, COLOURS_FLIP_ANTIDIAGONAL, COLOURS_HALF_TURN and COLOURS_FLIP_DIAGONAL.

DE += B, where B is the width in bytes. The counterpart at PREVIOUS_SPRITE_ROW subtracts instead, for the routines that read a sprite from the bottom up.