drainage_basin_cell_based.hpp

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/* Copyright (c) 2026 Otto Link. Distributed under the terms of the GNU General
   Public License. The full license is in the file LICENSE, distributed with
   this software. */
 
#pragma once
#include <functional>
#include <limits>
 
#include "highmap/array.hpp"
 
namespace hmap
{
 
enum FlowDirectionMethod : int
{
  FDM_D8,            
  FDM_PRIORITY_FLOOD 
};
 
class DrainageBasinCellBased
{
public:
  // --- Construction ---
 
  DrainageBasinCellBased() = default;
 
  DrainageBasinCellBased(const Array &z_);
 
  // --- Geometry / Mesh ---
 
  const Array &get_z() const;
 
  // --- Flow graph construction ---
 
  void compute_receivers(unsigned int seed = 0, float noise_strength = 0.f);
 
  void compute_receivers_priority_flood();
 
  void update_stream_tree(unsigned int seed, float noise_strength);
 
  void update_stream_tree();
 
  void update_traversals();
 
  std::vector<glm::ivec2> get_outlets() const;
 
  void set_outlets(const std::vector<glm::ivec2> &outlet_indices);
 
  std::vector<std::vector<glm::ivec2>> compute_upstream_traversals();
 
  // --- Basin topology utilities ---
 
  std::pair<Mat<glm::ivec2>, bool> find_subroots();
 
  void remove_lakes(const Mat<glm::ivec2> &subroot);
 
  std::vector<std::vector<glm::ivec2>> get_main_channels() const;
 
  // --- Hydrology computations ---
 
  Array compute_response_times(const Array &area_acc,
                               const Array &erodibility,
                               float        m_exp) const;
 
  float update_elevations(const Array &response_times,
                          float        uplift_rate,
                          const Array &max_slope);
 
  void accumulate_area_by_outlet(Array &acc) const;
 
  void flow_breach();
 
  // --- Members ---
 
  Array z; 
 
  Mat<int>                     outlets_mask; 
  Mat<glm::ivec2>              receivers;    
  Mat<std::vector<glm::ivec2>> children;     
  Mat<glm::ivec2>              roots;        
  // coordinates.
 
  std::unordered_map<glm::ivec2, std::vector<glm::ivec2>, IVec2Hash>
      traversals; 
  // Cached
  // traversal
  // paths.
 
  const glm::ivec2 null_cell = glm::ivec2(-1, -1); 
  // invalid/null cell.
 
private:
  // constants
  const int   di[8] = {1, 1, 0, -1, -1, -1, 0, 1};
  const int   dj[8] = {0, -1, -1, -1, 0, 1, 1, 1};
  const float cd[8] =
      {1.f, M_SQRT1_2, 1.f, M_SQRT1_2, 1.f, M_SQRT1_2, 1.f, M_SQRT1_2};
};
 
Mat<std::vector<glm::ivec2>> invert_receiver_map(
    const Mat<glm::ivec2> &receivers);
 
} // namespace hmap