6.4.7 Black Hole Warp

From [pov:6.7.12.6.1]:

BLACK_HOLE_WARP:
    warp
    {
        black_hole <Location>, Radius
        [BLACK_HOLE_ITEMS...]
    }
BLACK_HOLE_ITEMS:
    strength Strength | falloff Amount | inverse | type Type | 
    repeat <Repeat> | turbulence <Amount>

The minimal requirement is the black_hole keyword followed by a vector $\langle$Location$\rangle$ followed by a comma and a float Radius. Black holes effect all points within the spherical region around the location and within the radius. This is optionally followed by any number of other keywords which control how the texture is warped.

The amount of displacement of the point is given by the formula

   strength$$*d^{\text{falloff}},$$

where $d$ is the distance of the point from the complement of the ball around $\langle Location\rangle$ with radius 1, so $d=0$ outside this ball and $d=1$ on its center.

The keyword inverse reverses the direction of the displacement.

The phrase repeat V makes black holes at the lattice points specified by the components of $V$.