PrusaSlicer-NonPlainar/src/libslic3r/SLA/Clustering.hpp

#ifndef SLA_CLUSTERING_HPP
#define SLA_CLUSTERING_HPP

#include <vector>

#include <libslic3r/Point.hpp>
#include <libslic3r/SLA/SpatIndex.hpp>

namespace Slic3r { namespace sla {

using ClusterEl = std::vector<unsigned>;
using ClusteredPoints = std::vector<ClusterEl>;

// Clustering a set of points by the given distance.
ClusteredPoints cluster(const std::vector<unsigned>& indices,
                        std::function<Vec3d(unsigned)> pointfn,
                        double dist,
                        unsigned max_points);

ClusteredPoints cluster(const Eigen::MatrixXd& points,
                        double dist,
                        unsigned max_points);

ClusteredPoints cluster(
    const std::vector<unsigned>& indices,
    std::function<Vec3d(unsigned)> pointfn,
    std::function<bool(const PointIndexEl&, const PointIndexEl&)> predicate,
    unsigned max_points);

// This function returns the position of the centroid in the input 'clust'
// vector of point indices.
template<class DistFn, class PointFn>
long cluster_centroid(const ClusterEl &clust, PointFn pointfn, DistFn df)
{
    switch(clust.size()) {
    case 0: /* empty cluster */ return -1;
    case 1: /* only one element */ return 0;
    case 2: /* if two elements, there is no center */ return 0;
    default: ;
    }

    // The function works by calculating for each point the average distance
    // from all the other points in the cluster. We create a selector bitmask of
    // the same size as the cluster. The bitmask will have two true bits and
    // false bits for the rest of items and we will loop through all the
    // permutations of the bitmask (combinations of two points). Get the
    // distance for the two points and add the distance to the averages.
    // The point with the smallest average than wins.

    // The complexity should be O(n^2) but we will mostly apply this function
    // for small clusters only (cca 3 elements)

    std::vector<bool> sel(clust.size(), false);   // create full zero bitmask
    std::fill(sel.end() - 2, sel.end(), true);    // insert the two ones
    std::vector<double> avgs(clust.size(), 0.0);  // store the average distances

    do {
        std::array<size_t, 2> idx;
        for(size_t i = 0, j = 0; i < clust.size(); i++)
            if(sel[i]) idx[j++] = i;

        double d = df(pointfn(clust[idx[0]]),
                      pointfn(clust[idx[1]]));

        // add the distance to the sums for both associated points
        for(auto i : idx) avgs[i] += d;

        // now continue with the next permutation of the bitmask with two 1s
    } while(std::next_permutation(sel.begin(), sel.end()));

    // Divide by point size in the cluster to get the average (may be redundant)
    for(auto& a : avgs) a /= clust.size();

    // get the lowest average distance and return the index
    auto minit = std::min_element(avgs.begin(), avgs.end());
    return long(minit - avgs.begin());
}


}} // namespace Slic3r::sla

#endif // CLUSTERING_HPP