Sparse grid bfs (#942)

* Add a utility function which computes a sparse set of epsilon-sized grid cells surrounding an input surface. The function takes a point on the surface as input and finds all those epsilon grid cells that intersect the surface using a breadth first search over the grid space.

* Add a utility function which computes a sparse set of epsilon-sized grid cells surrounding an input surface. The function takes a point on the surface as input and finds all those epsilon grid cells that intersect the surface using a breadth first search over the grid space.


Former-commit-id: 1dbd225d993a5417c7d3bedc3a6ba354cc256956

tutorial/715_MeshImplicitFunction/main.cpp

@@ -34,7 +34,7 @@ int main(int argc, char * argv[])
   Eigen::MatrixXi CI;
 
   // Construct the voxel grid, populating CS, CV, and CI
-  igl::sparse_voxel_grid(p0, scalar_func, eps, CS, CV, CI);
+  igl::sparse_voxel_grid(p0, scalar_func, eps, 1024 /*expected_number_of_cubes*/, CS, CV, CI);
 
   // Given the sparse voxel grid, use Marching Cubes to construct a triangle mesh of the surface
   Eigen::MatrixXi F;