Args:
        box: 4 float
        mask: MxM floats
        shape: h,w
    Returns:
        A uint8 binary image of hxw.

def _paste_mask(box, mask, shape):
    """
    Args:
        box: 4 float
        mask: MxM floats
        shape: h,w
    Returns:
        A uint8 binary image of hxw.
    """
    # int() is floor
    # box fpcoor=0.0 -> intcoor=0.0
    x0, y0 = list(map(int, box[:2] + 0.5))
    # box fpcoor=h -> intcoor=h-1, inclusive
    x1, y1 = list(map(int, box[2:] - 0.5))    # inclusive
    x1 = max(x0, x1)    # require at least 1x1
    y1 = max(y0, y1)

    w = x1 + 1 - x0
    h = y1 + 1 - y0

    # rounding errors could happen here, because masks were not originally computed for this shape.
    # but it's hard to do better, because the network does not know the "original" scale
    mask = (cv2.resize(mask, (w, h)) > 0.5).astype('uint8')
    ret = np.zeros(shape, dtype='uint8')
    ret[y0:y1 + 1, x0:x1 + 1] = mask
    return ret