// pattern modifier
  // (---black_hole warp---)
  // local deformation of the pattern
  warp {
    black_hole <0.5, 0.5, 0>, 0.25   // position and radius
    //strength 3                     // strength of deformation
    //inverse                        // invert effect
    //repeat <1.5, 1, 0>             // repeat black hole
    //turbulence <0.1, 0.4, 0>       // turbulate repeat position
  }