SoftGroup/softgroup/ops/src/bfs_cluster/bfs_cluster.cpp

/*
Ball Query with BatchIdx & Clustering Algorithm
Written by Li Jiang
All Rights Reserved 2020.

Modified by Thang Vu - Remove semantic label in clustering
*/

#include "bfs_cluster.h"

/* =================== ballquery_batch_p================================= */
// input xyz: (n, 3) float
// input batch_idxs: (n) int
// input batch_offsets: (B+1) int, batch_offsets[-1]
// output idx: (n * meanActive) dim 0 for number of points in the ball, idx in n
// output start_len: (n, 2), int
int ballquery_batch_p(at::Tensor xyz_tensor, at::Tensor batch_idxs_tensor,
                      at::Tensor batch_offsets_tensor, at::Tensor idx_tensor,
                      at::Tensor start_len_tensor, int n, int meanActive,
                      float radius) {
  const float *xyz = xyz_tensor.data_ptr<float>();
  const int *batch_idxs = batch_idxs_tensor.data_ptr<int>();
  const int *batch_offsets = batch_offsets_tensor.data_ptr<int>();
  int *idx = idx_tensor.data_ptr<int>();
  int *start_len = start_len_tensor.data_ptr<int>();

  cudaStream_t stream = at::cuda::getCurrentCUDAStream();
  int cumsum = ballquery_batch_p_cuda(n, meanActive, radius, xyz, batch_idxs,
                                      batch_offsets, idx, start_len, stream);
  return cumsum;
}

ConnectedComponent find_cc(Int idx, Int *ball_query_idxs, int *start_len,
                           int *visited) {
  ConnectedComponent cc;
  cc.addPoint(idx);
  visited[idx] = 1;

  std::queue<Int> Q;
  assert(Q.empty());
  Q.push(idx);

  while (!Q.empty()) {
    Int cur = Q.front();
    Q.pop();
    int start = start_len[cur * 2];
    int len = start_len[cur * 2 + 1];
    for (Int i = start; i < start + len; i++) {
      Int idx_i = ball_query_idxs[i];
      if (visited[idx_i] == 1)
        continue;
      cc.addPoint(idx_i);
      visited[idx_i] = 1;
      Q.push(idx_i);
    }
  }
  return cc;
}

int get_clusters(float *class_numpoint_mean, int *ball_query_idxs,
                 int *start_len, const int nPoint, float threshold,
                 ConnectedComponents &clusters, const int class_id) {
  int *visited = new int[nPoint]{0};
  float _class_numpoint_mean, thr;
  int sumNPoint = 0;

  for (int i = 0; i < nPoint; i++) {
    if (visited[i] == 0) {
      ConnectedComponent CC = find_cc(i, ball_query_idxs, start_len, visited);
      _class_numpoint_mean = class_numpoint_mean[class_id];

      // if _class_num_point_mean is not defined (-1) directly use threshold
      if (_class_numpoint_mean == -1) {
        thr = threshold;
      } else {
        thr = threshold * _class_numpoint_mean;
      }
      if ((int)CC.pt_idxs.size() >= thr) {
        clusters.push_back(CC);
        sumNPoint += (int)CC.pt_idxs.size();
      }
    }
  }
  delete[] visited;
  return sumNPoint;
}

// convert from ConnectedComponents to (idxs, offsets) representation
void fill_cluster_idxs_(ConnectedComponents &CCs, int *cluster_idxs,
                        int *cluster_offsets) {
  for (int i = 0; i < (int)CCs.size(); i++) {
    cluster_offsets[i + 1] = cluster_offsets[i] + (int)CCs[i].pt_idxs.size();
    for (int j = 0; j < (int)CCs[i].pt_idxs.size(); j++) {
      int idx = CCs[i].pt_idxs[j];
      cluster_idxs[(cluster_offsets[i] + j) * 2 + 0] = i;
      cluster_idxs[(cluster_offsets[i] + j) * 2 + 1] = idx;
    }
  }
}

// input: class_numpoint_mean_tensor
// input: ball_query_idxs, int, (nActive)
// input: start_len, int, (N, 2)
// output: cluster_idxs, int (sumNPoint, 2), dim 0 for cluster_id, dim 1 for
// corresponding point idxs in N
// output: cluster_offsets, int (nCluster + 1)
void bfs_cluster(at::Tensor class_numpoint_mean_tensor,
                 at::Tensor ball_query_idxs_tensor, at::Tensor start_len_tensor,
                 at::Tensor cluster_idxs_tensor,
                 at::Tensor cluster_offsets_tensor, const int N,
                 float threshold, const int class_id) {
  float *class_numpoint_mean = class_numpoint_mean_tensor.data_ptr<float>();
  Int *ball_query_idxs = ball_query_idxs_tensor.data_ptr<Int>();
  int *start_len = start_len_tensor.data_ptr<int>();
  ConnectedComponents CCs;
  int sumNPoint = get_clusters(class_numpoint_mean, ball_query_idxs, start_len,
                               N, threshold, CCs, class_id);
  int nCluster = (int)CCs.size();
  cluster_idxs_tensor.resize_({sumNPoint, 2});
  cluster_offsets_tensor.resize_({nCluster + 1});
  cluster_idxs_tensor.zero_();
  cluster_offsets_tensor.zero_();
  int *cluster_idxs = cluster_idxs_tensor.data_ptr<int>();
  int *cluster_offsets = cluster_offsets_tensor.data_ptr<int>();
  fill_cluster_idxs_(CCs, cluster_idxs, cluster_offsets);
}