rem: else if (second->count == 0	|| !valid_rect(sect_rect(first->bound, second->bound)))
add: else if (second->count == 0	|| !rects_intersect(first->bound, second->bound))
context: sub_region(BRegion *first, BRegion *second, BRegion *dest){	PRINT(("%s\n", __PRETTY_FUNCTION__));	ASSERT(first);	ASSERT(second);	ASSERT(dest);	if (first->count == 0)		zero_region(dest);			else if (second->count == 0	|| !valid_rect(sect_rect(first->bound, second->bound)))		copy_region(first, dest);			else		sub_region_complex(second, first, dest);	}