assimp/code/SpatialSort.cpp

/*
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Open Asset Import Library (ASSIMP)
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/** @file Implementation of the helper class to quickly find vertices close to a given position */
#include <algorithm>
#include "SpatialSort.h"

using namespace Assimp;

// ------------------------------------------------------------------------------------------------
// Constructs a spatially sorted representation from the given position array.
SpatialSort::SpatialSort( const aiVector3D* pPositions, unsigned int pNumPositions, unsigned int pElementOffset)
{
	// define the reference plane. We choose some arbitrary vector away from all basic axises 
	// in the hope that no model spreads all its vertices along this plane.
	mPlaneNormal.Set( 0.8523f, 0.34321f, 0.5736f);
	mPlaneNormal.Normalize();

	// store references to all given positions along with their distance to the reference plane
	mPositions.reserve( 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);

		// store position by index and distance
		float distance = *vec * mPlaneNormal;
		mPositions.push_back( Entry( a, *vec, distance));
	}

	// now sort the array ascending by distance.
	std::sort( mPositions.begin(), mPositions.end());
}

// ------------------------------------------------------------------------------------------------
// Destructor
SpatialSort::~SpatialSort()
{
	// nothing to do here, everything destructs automatically
}

// ------------------------------------------------------------------------------------------------
// Returns an iterator for all positions close to the given position.
void SpatialSort::FindPositions( const aiVector3D& pPosition, float pRadius, std::vector<unsigned int>& poResults) const
{
	float dist = pPosition * mPlaneNormal;
	float minDist = dist - pRadius, maxDist = dist + pRadius;

	// clear the array in this strange fashion because a simple clear() would also deallocate
    // the array which we want to avoid
	poResults.erase( poResults.begin(), poResults.end());

	// 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 = mPositions.size() / 2;
	unsigned int binaryStepSize = 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 aray
	std::vector<Entry>::const_iterator it = mPositions.begin() + index;
	float squareEpsilon = pRadius * pRadius;
	while( it->mDistance < maxDist)
	{
		if( (it->mPosition - pPosition).SquareLength() < squareEpsilon)
			poResults.push_back( it->mIndex);
		++it;
		if( it == mPositions.end())
			break;
	}

	// that's it
}