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/** @file Implementation of the helper class to quickly find vertices close to a given position */

#include <assimp/SpatialSort.h>

#include <assimp/ai_assert.h>

using namespace Assimp;

// CHAR_BIT seems to be defined under MVSC, but not under GCC. Pray that the correct value is 8.

#ifndef CHAR_BIT

#define CHAR_BIT 8

#endif

const aiVector3D PlaneInit(0.8523f, 0.34321f, 0.5736f);

// ------------------------------------------------------------------------------------------------

// Constructs a spatially sorted representation from the given position array.

// define the reference plane. We choose some arbitrary vector away from all basic axes

// in the hope that no model spreads all its vertices along this plane.

SpatialSort::SpatialSort(const aiVector3D *pPositions, unsigned int pNumPositions, unsigned int pElementOffset) :

        mPlaneNormal(PlaneInit),

        mFinalized(false) {

    mPlaneNormal.Normalize();

    Fill(pPositions, pNumPositions, pElementOffset);

}

// ------------------------------------------------------------------------------------------------

SpatialSort::SpatialSort() :

        mPlaneNormal(PlaneInit),

        mFinalized(false) {

    mPlaneNormal.Normalize();

}

// ------------------------------------------------------------------------------------------------

void SpatialSort::Fill(const aiVector3D *pPositions, unsigned int pNumPositions,

        unsigned int pElementOffset,

        bool pFinalize /*= true */) {

    mPositions.clear();

    mFinalized = false;

    Append(pPositions, pNumPositions, pElementOffset, pFinalize);

    mFinalized = pFinalize;

}

// ------------------------------------------------------------------------------------------------

ai_real SpatialSort::CalculateDistance(const aiVector3D &pPosition) const {

    return (pPosition - mCentroid) * mPlaneNormal;

}

// ------------------------------------------------------------------------------------------------

void SpatialSort::Finalize() {

    const ai_real scale = 1.0f / mPositions.size();

    for (unsigned int i = 0; i < mPositions.size(); i++) {

        mCentroid += scale * mPositions[i].mPosition;

    }

    for (unsigned int i = 0; i < mPositions.size(); i++) {

        mPositions[i].mDistance = CalculateDistance(mPositions[i].mPosition);

    }

    std::sort(mPositions.begin(), mPositions.end());

    mFinalized = true;

}

// ------------------------------------------------------------------------------------------------

void SpatialSort::Append(const aiVector3D *pPositions, unsigned int pNumPositions,

        unsigned int pElementOffset,

        bool pFinalize /*= true */) {

    ai_assert(!mFinalized && "You cannot add positions to the SpatialSort object after it has been finalized.");

    // store references to all given positions along with their distance to the reference plane

    const size_t initial = mPositions.size();

    mPositions.reserve(initial + pNumPositions);

    for (unsigned int a = 0; a < pNumPositions; a++) {

        const char *tempPointer = reinterpret_cast<const char *>(pPositions);

        const aiVector3D *vec = reinterpret_cast<const aiVector3D *>(tempPointer + a * pElementOffset);

        mPositions.emplace_back(static_cast<unsigned int>(a + initial), *vec);

    }

    if (pFinalize) {

        // now sort the array ascending by distance.

        Finalize();

    }

}

// ------------------------------------------------------------------------------------------------

// Returns an iterator for all positions close to the given position.

void SpatialSort::FindPositions(const aiVector3D &pPosition,

        ai_real pRadius, std::vector<unsigned int> &poResults) const {

    ai_assert(mFinalized && "The SpatialSort object must be finalized before FindPositions can be called.");

    const ai_real dist = CalculateDistance(pPosition);

    const ai_real minDist = dist - pRadius, maxDist = dist + pRadius;

    // clear the array

    poResults.clear();

    // quick check for positions outside the range

    if (mPositions.size() == 0)

        return;

    if (maxDist < mPositions.front().mDistance)

        return;

    if (minDist > mPositions.back().mDistance)

        return;

    // do a binary search for the minimal distance to start the iteration there

    unsigned int index = (unsigned int)mPositions.size() / 2;

    unsigned int binaryStepSize = (unsigned int)mPositions.size() / 4;

    while (binaryStepSize > 1) {

        if (mPositions[index].mDistance < minDist)

            index += binaryStepSize;

        else

            index -= binaryStepSize;

        binaryStepSize /= 2;

    }

    // depending on the direction of the last step we need to single step a bit back or forth

    // to find the actual beginning element of the range

    while (index > 0 && mPositions[index].mDistance > minDist)

        index--;

    while (index < (mPositions.size() - 1) && mPositions[index].mDistance < minDist)

        index++;

    // Mow start iterating from there until the first position lays outside of the distance range.

    // Add all positions inside the distance range within the given radius to the result array

    std::vector<Entry>::const_iterator it = mPositions.begin() + index;

    const ai_real pSquared = pRadius * pRadius;

    while (it->mDistance < maxDist) {

        if ((it->mPosition - pPosition).SquareLength() < pSquared)

            poResults.push_back(it->mIndex);

        ++it;

        if (it == mPositions.end())

            break;

    }

    // that's it

}

namespace {

// Binary, signed-integer representation of a single-precision floating-point value.

// IEEE 754 says: "If two floating-point numbers in the same format are ordered then they are

//  ordered the same way when their bits are reinterpreted as sign-magnitude integers."

// This allows us to convert all floating-point numbers to signed integers of arbitrary size

//  and then use them to work with ULPs (Units in the Last Place, for high-precision

//  computations) or to compare them (integer comparisons are faster than floating-point

//  comparisons on many platforms).

typedef ai_int BinFloat;

// --------------------------------------------------------------------------------------------

// Converts the bit pattern of a floating-point number to its signed integer representation.

BinFloat ToBinary(const ai_real &pValue) {

    // If this assertion fails, signed int is not big enough to store a float on your platform.

    //  Please correct the declaration of BinFloat a few lines above - but do it in a portable,

    //  #ifdef'd manner!

    static_assert(sizeof(BinFloat) >= sizeof(ai_real), "sizeof(BinFloat) >= sizeof(ai_real)");

#if defined(_MSC_VER)

    // If this assertion fails, Visual C++ has finally moved to ILP64. This means that this

    //  code has just become legacy code! Find out the current value of _MSC_VER and modify

    //  the #if above so it evaluates false on the current and all upcoming VC versions (or

    //  on the current platform, if LP64 or LLP64 are still used on other platforms).

    static_assert(sizeof(BinFloat) == sizeof(ai_real), "sizeof(BinFloat) == sizeof(ai_real)");

    // This works best on Visual C++, but other compilers have their problems with it.

    const BinFloat binValue = reinterpret_cast<BinFloat const &>(pValue);

    //::memcpy(&binValue, &pValue, sizeof(pValue));

    //return binValue;

#else

    // On many compilers, reinterpreting a float address as an integer causes aliasing

    // problems. This is an ugly but more or less safe way of doing it.

    union {

        ai_real asFloat;

        BinFloat asBin;

    } conversion;

    conversion.asBin = 0; // zero empty space in case sizeof(BinFloat) > sizeof(float)

    conversion.asFloat = pValue;

    const BinFloat binValue = conversion.asBin;

#endif

    // floating-point numbers are of sign-magnitude format, so find out what signed number

    //  representation we must convert negative values to.

    // See http://en.wikipedia.org/wiki/Signed_number_representations.

    const BinFloat mask = BinFloat(1) << (CHAR_BIT * sizeof(BinFloat) - 1);

    // Two's complement?

    const bool DefaultValue = ((-42 == (~42 + 1)) && (binValue & mask));

    const bool OneComplement = ((-42 == ~42) && (binValue & mask));

    if (DefaultValue)

        return mask - binValue;

    // One's complement?

    else if (OneComplement)

        return BinFloat(-0) - binValue;

    // Sign-magnitude? -0 = 1000... binary

    return binValue;

}

} // namespace

// ------------------------------------------------------------------------------------------------

// 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.

void SpatialSort::FindIdenticalPositions(const aiVector3D &pPosition, std::vector<unsigned int> &poResults) const {

    ai_assert(mFinalized && "The SpatialSort object must be finalized before FindIdenticalPositions can be called.");

    // Epsilons have a huge disadvantage: they are of constant precision, while floating-point

    //  values are of log2 precision. If you apply e=0.01 to 100, the epsilon is rather small, but

    //  if you apply it to 0.001, it is enormous.

    // The best way to overcome this is the unit in the last place (ULP). A precision of 2 ULPs

    //  tells us that a float does not differ more than 2 bits from the "real" value. ULPs are of

    //  logarithmic precision - around 1, they are 1*(2^24) and around 10000, they are 0.00125.

    // For standard C math, we can assume a precision of 0.5 ULPs according to IEEE 754. The

    //  incoming vertex positions might have already been transformed, probably using rather

    //  inaccurate SSE instructions, so we assume a tolerance of 4 ULPs to safely identify

    //  identical vertex positions.

    static const int toleranceInULPs = 4;

    // An interesting point is that the inaccuracy grows linear with the number of operations:

    //  multiplying to numbers, each inaccurate to four ULPs, results in an inaccuracy of four ULPs

    //  plus 0.5 ULPs for the multiplication.

    // To compute the distance to the plane, a dot product is needed - that is a multiplication and

    //  an addition on each number.

    static const int distanceToleranceInULPs = toleranceInULPs + 1;

    // The squared distance between two 3D vectors is computed the same way, but with an additional

    //  subtraction.

    static const int distance3DToleranceInULPs = distanceToleranceInULPs + 1;

    // Convert the plane distance to its signed integer representation so the ULPs tolerance can be

    //  applied. For some reason, VC won't optimize two calls of the bit pattern conversion.

    const BinFloat minDistBinary = ToBinary(CalculateDistance(pPosition)) - distanceToleranceInULPs;

    const BinFloat maxDistBinary = minDistBinary + 2 * distanceToleranceInULPs;

    // clear the array in this strange fashion because a simple clear() would also deallocate

    // the array which we want to avoid

    poResults.resize(0);

    // do a binary search for the minimal distance to start the iteration there

    unsigned int index = (unsigned int)mPositions.size() / 2;

    unsigned int binaryStepSize = (unsigned int)mPositions.size() / 4;

    while (binaryStepSize > 1) {

        // Ugly, but conditional jumps are faster with integers than with floats

        if (minDistBinary > ToBinary(mPositions[index].mDistance))

            index += binaryStepSize;

        else

            index -= binaryStepSize;

        binaryStepSize /= 2;

    }

    // depending on the direction of the last step we need to single step a bit back or forth

    // to find the actual beginning element of the range

    while (index > 0 && minDistBinary < ToBinary(mPositions[index].mDistance))

        index--;

    while (index < (mPositions.size() - 1) && minDistBinary > ToBinary(mPositions[index].mDistance))

        index++;

    // Now start iterating from there until the first position lays outside of the distance range.

    // Add all positions inside the distance range within the tolerance to the result array

    std::vector<Entry>::const_iterator it = mPositions.begin() + index;

    while (ToBinary(it->mDistance) < maxDistBinary) {

        if (distance3DToleranceInULPs >= ToBinary((it->mPosition - pPosition).SquareLength()))

            poResults.push_back(it->mIndex);

        ++it;

        if (it == mPositions.end())

            break;

    }

    // that's it

}

// ------------------------------------------------------------------------------------------------

unsigned int SpatialSort::GenerateMappingTable(std::vector<unsigned int> &fill, ai_real pRadius) const {

    ai_assert(mFinalized && "The SpatialSort object must be finalized before GenerateMappingTable can be called.");

    fill.resize(mPositions.size(), UINT_MAX);

    ai_real dist, maxDist;

    unsigned int t = 0;

    const ai_real pSquared = pRadius * pRadius;

    for (size_t i = 0; i < mPositions.size();) {

        dist = (mPositions[i].mPosition - mCentroid) * mPlaneNormal;

        maxDist = dist + pRadius;

        fill[mPositions[i].mIndex] = t;

        const aiVector3D &oldpos = mPositions[i].mPosition;

        for (++i; i < fill.size() && mPositions[i].mDistance < maxDist && (mPositions[i].mPosition - oldpos).SquareLength() < pSquared; ++i) {

            fill[mPositions[i].mIndex] = t;

        }

        ++t;

    }

#ifdef ASSIMP_BUILD_DEBUG

    // debug invariant: mPositions[i].mIndex values must range from 0 to mPositions.size()-1

    for (size_t i = 0; i < fill.size(); ++i) {

        ai_assert(fill[i] < mPositions.size());

    }

#endif

    return t;

}