docs: def piece_wise_linear(scale, points):
    """Create a palette that is piece-wise linear given some colors at points."""
    assert len(points) >= 2
    assert points[0][0] == 0
    assert points[-1][0] == 1
    assert all(i < j for i, j in zip(points[:-1], points[1:]))
    out = numpy.zeros((scale, 3))
    p1, c1 = points[0]
    p2, c2 = points[1]
    next_pt = 2
  
    for i in range(1, scale):
      v = i / scale
      if v > p2:
        p1, c1 = p2, c2
        p2, c2 = points[next_pt]
        next_pt += 1
      frac = (v - p1) / (p2 - p1)
      out[i, :] = c1 * (1 - frac) + c2 * frac
    return out