title: fast sphere-grid intersection
body: <p>given a 3D grid, a 3d point as sphere center and a radius, i'd like to quickly calculate all cells contained or intersected by the sphere.</p>
  
  <p>Currently i take the the (gridaligned) boundingbox of the sphere and calculate the two cells for the min anx max point of this boundingbox. then, for each cell between those two cells, i do a box-sphere intersection test.</p>
  
  <p>would be great if there was something more efficient</p>
  
  <p>thanks!</p>