GaussianCloud.hpp

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// SPDX-FileCopyrightText: 2026 Povl Filip Sonne-Frederiksen
//
// SPDX-License-Identifier: GPL-3.0-or-later
 
#pragma once
 
#include <array>
#include <cstddef>
#include <cstdint>
#include <filesystem>
#include <vector>
 
#include <reusex/types/point_types.hpp>
 
namespace reusex::gsplat {

inline constexpr float kShC0 = 0.28209479177387814f;

inline float rgb_to_sh_dc(float c) { return (c - 0.5f) / kShC0; }

inline float sh_dc_to_rgb(float f) { return f * kShC0 + 0.5f; }

float inverse_sigmoid(float x);

struct GaussianCloud {
  std::vector<std::array<float, 3>> means;  
  std::vector<std::array<float, 3>> scales; 
  std::vector<std::array<float, 4>> quats;  
  std::vector<float> opacities;             
  std::vector<std::array<float, 3>> sh_dc;  
  std::vector<std::vector<float>> sh_rest;
  int sh_degree = 0; 
 
  std::size_t size() const { return means.size(); }
  bool empty() const { return means.empty(); }

  void validate() const;
};

struct GaussianInitOptions {
  int knn = 3;

  float initial_opacity = 0.1f;

  float min_scale = 1e-4f;
  float max_scale = 0.5f;

  int sh_degree = 0;

  std::size_t max_points = 0;
};

GaussianCloud init_from_point_cloud(const CloudPtr &cloud,
                                    const GaussianInitOptions &opt = {});

std::vector<std::uint8_t> gaussian_ply_bytes(const GaussianCloud &gaussians);

void save_gaussian_ply(const GaussianCloud &gaussians,
                       const std::filesystem::path &path);

GaussianCloud load_gaussian_ply(const std::filesystem::path &path);
 
} // namespace reusex::gsplat