bvh.h

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#pragma once
#include <optional>
#include "vde/spatial/spatial_index.h"
#include "vde/core/aabb.h"
#include "vde/core/triangle.h"
 
namespace vde::spatial {
using core::Point3D;
using core::Vector3D;
using core::Ray3Dd;
using core::Triangle3D;
 
enum class BVHSplitStrategy {
    Middle,  
    Equal,   
    SAH      
};
 
struct BVHBuildOptions {
    BVHSplitStrategy strategy = BVHSplitStrategy::SAH;  
    int leaf_size = 4;     
    int max_depth = 64;    
};
 
class BVH : public SpatialIndex<Triangle3D> {
public:
    explicit BVH(const BVHBuildOptions& opts = {}) : opts_(opts) {}
 
    void build(const std::vector<Triangle3D>& tris) override;
 
    void insert(const Triangle3D& tri) override;
 
    bool remove(const Triangle3D& tri) override;
 
    std::vector<Triangle3D> query_range(const AABB3D& range) const override;
 
    std::vector<Triangle3D> query_knn(const Point3D& point, size_t k) const override;
 
    std::vector<Triangle3D> query_ray(const Ray3Dd& ray) const override;
 
    void clear() override;
 
    size_t size() const override { return primitives_.size(); }
 
    struct HitResult {
        double t;          
        Triangle3D tri;    
        Point3D point;     
    };
 
    std::optional<HitResult> query_ray_nearest(const Ray3Dd& ray) const;
 
private:
    struct Node {
        AABB3D bounds;          
        int left = -1;          
        int right = -1;         
        int first_prim = 0;     
        int prim_count = 0;     
        bool leaf() const { return left < 0; }
    };
 
    std::vector<Node> nodes_;               
    std::vector<Triangle3D> primitives_;    
    BVHBuildOptions opts_;                  
    void build_recursive(int node, int first, int count, int depth);
 
    double sah_cost(int n_left, int n_right, const AABB3D& left, const AABB3D& right) const;
};
 
}  // namespace vde::spatial