assimp/include/assimp/SpatialSort.h

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/** Small helper classes to optimise finding vertizes close to a given location */
#pragma once
#ifndef AI_SPATIALSORT_H_INC
#define AI_SPATIALSORT_H_INC

#ifdef __GNUC__
#pragma GCC system_header
#endif

#include <assimp/types.h>
#include <vector>
#include <limits>

namespace Assimp {

// ------------------------------------------------------------------------------------------------
/** A little helper class to quickly find all vertices in the epsilon environment of a given
 * position. Construct an instance with an array of positions. The class stores the given positions
 * by their indices and sorts them by their distance to an arbitrary chosen plane.
 * You can then query the instance for all vertices close to a given position in an average O(log n)
 * time, with O(n) worst case complexity when all vertices lay on the plane. The plane is chosen
 * so that it avoids common planes in usual data sets. */
// ------------------------------------------------------------------------------------------------
class ASSIMP_API SpatialSort {
public:
    SpatialSort();

    // ------------------------------------------------------------------------------------
    /** Constructs a spatially sorted representation from the given position array.
     * Supply the positions in its layout in memory, the class will only refer to them
     * by index.
     * @param pPositions Pointer to the first position vector of the array.
     * @param pNumPositions Number of vectors to expect in that array.
     * @param pElementOffset Offset in bytes from the beginning of one vector in memory
     *   to the beginning of the next vector. */
    SpatialSort(const aiVector3D *pPositions, unsigned int pNumPositions,
            unsigned int pElementOffset);

    /** Destructor */
    ~SpatialSort() = default;

    // ------------------------------------------------------------------------------------
    /** Sets the input data for the SpatialSort. This replaces existing data, if any.
     *  The new data receives new indices in ascending order.
     *
     * @param pPositions Pointer to the first position vector of the array.
     * @param pNumPositions Number of vectors to expect in that array.
     * @param pElementOffset Offset in bytes from the beginning of one vector in memory
     *   to the beginning of the next vector.
     * @param pFinalize Specifies whether the SpatialSort's internal representation
     *   is finalized after the new data has been added. Finalization is
     *   required in order to use #FindPosition() or #GenerateMappingTable().
     *   If you don't finalize yet, you can use #Append() to add data from
     *   other sources.*/
    void Fill(const aiVector3D *pPositions, unsigned int pNumPositions,
            unsigned int pElementOffset,
            bool pFinalize = true);

    // ------------------------------------------------------------------------------------
    /** Same as #Fill(), except the method appends to existing data in the #SpatialSort. */
    void Append(const aiVector3D *pPositions, unsigned int pNumPositions,
            unsigned int pElementOffset,
            bool pFinalize = true);

    // ------------------------------------------------------------------------------------
    /** Finalize the spatial hash data structure. This can be useful after
     *  multiple calls to #Append() with the pFinalize parameter set to false.
     *  This is finally required before one of #FindPositions() and #GenerateMappingTable()
     *  can be called to query the spatial sort.*/
    void Finalize();

    // ------------------------------------------------------------------------------------
    /** Returns an iterator for all positions close to the given position.
     * @param pPosition The position to look for vertices.
     * @param pRadius Maximal distance from the position a vertex may have to be counted in.
     * @param poResults The container to store the indices of the found positions.
     *   Will be emptied by the call so it may contain anything.
     * @return An iterator to iterate over all vertices in the given area.*/
    void FindPositions(const aiVector3D &pPosition, ai_real pRadius,
            std::vector<unsigned int> &poResults) const;

    // ------------------------------------------------------------------------------------
    /** Fills an array with indices of all positions identical to the given position. In
     *  opposite to FindPositions(), not an epsilon is used but a (very low) tolerance of
     *  four floating-point units.
     * @param pPosition The position to look for vertices.
     * @param poResults The container to store the indices of the found positions.
     *   Will be emptied by the call so it may contain anything.*/
    void FindIdenticalPositions(const aiVector3D &pPosition,
            std::vector<unsigned int> &poResults) const;

    // ------------------------------------------------------------------------------------
    /** Compute a table that maps each vertex ID referring to a spatially close
     *  enough position to the same output ID. Output IDs are assigned in ascending order
     *  from 0...n.
     * @param fill Will be filled with numPositions entries.
     * @param pRadius Maximal distance from the position a vertex may have to
     *   be counted in.
     *  @return Number of unique vertices (n).  */
    unsigned int GenerateMappingTable(std::vector<unsigned int> &fill,
            ai_real pRadius) const;

protected:
    /** Return the distance to the sorting plane. */
    ai_real CalculateDistance(const aiVector3D &pPosition) const;

protected:
    /** Normal of the sorting plane, normalized.
     */
    aiVector3D mPlaneNormal;

    /** The centroid of the positions, which is used as a point on the sorting plane
     * when calculating distance. This value is calculated in Finalize.
    */
    aiVector3D mCentroid;

    /** An entry in a spatially sorted position array. Consists of a vertex index,
     * its position and its pre-calculated distance from the reference plane */
    struct Entry {
        unsigned int mIndex; ///< The vertex referred by this entry
        aiVector3D mPosition; ///< Position
        /// Distance of this vertex to the sorting plane. This is set by Finalize.
        ai_real mDistance;

        Entry() AI_NO_EXCEPT
                : mIndex(std::numeric_limits<unsigned int>::max()),
                  mPosition(),
                  mDistance(std::numeric_limits<ai_real>::max()) {
            // empty
        }
        Entry(unsigned int pIndex, const aiVector3D &pPosition) :
                mIndex(pIndex), mPosition(pPosition), mDistance(std::numeric_limits<ai_real>::max()) {
            // empty
        }

        bool operator<(const Entry &e) const { return mDistance < e.mDistance; }
    };

    // all positions, sorted by distance to the sorting plane
    std::vector<Entry> mPositions;

    /// false until the Finalize method is called.
    bool mFinalized;
};

} // end of namespace Assimp

#endif // AI_SPATIALSORT_H_INC