def legacy_position_transform(positions):
    """
    Transforms positions in the tree sequence into VCF coordinates under
    the pre 0.2.0 legacy rule.
    """
    last_pos = 0
    transformed = []
    for pos in positions:
        pos = int(round(pos))
        if pos <= last_pos:
            pos = last_pos + 1
        transformed.append(pos)
        last_pos = pos
    return transformed