Create view frustum matrix.

def frustum(left, right, bottom, top, znear, zfar):
  """Create view frustum matrix."""
  assert right != left
  assert bottom != top
  assert znear != zfar

  M = np.zeros((4, 4), dtype=np.float32)
  M[0, 0] = +2.0 * znear / (right - left)
  M[2, 0] = (right + left) / (right - left)
  M[1, 1] = +2.0 * znear / (top - bottom)
  M[3, 1] = (top + bottom) / (top - bottom)
  M[2, 2] = -(zfar + znear) / (zfar - znear)
  M[3, 2] = -2.0 * znear * zfar / (zfar - znear)
  M[2, 3] = -1.0
  return M