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 "AssimpPCH.h"
#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(0.8523f, 0.34321f, 0.5736f)
{
	mPlaneNormal.Normalize();
	Fill(pPositions,pNumPositions,pElementOffset);
}

// ------------------------------------------------------------------------------------------------
SpatialSort :: SpatialSort()
: mPlaneNormal(0.8523f, 0.34321f, 0.5736f)
{
	mPlaneNormal.Normalize();
}

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

// ------------------------------------------------------------------------------------------------
void SpatialSort::Fill( const aiVector3D* pPositions, unsigned int pNumPositions, 
	unsigned int pElementOffset,
	bool pFinalize /*= true */)
{
	mPositions.clear();
	Append(pPositions,pNumPositions,pElementOffset,pFinalize);
}

// ------------------------------------------------------------------------------------------------
void SpatialSort :: Finalize()
{
	std::sort( mPositions.begin(), mPositions.end());
}

// ------------------------------------------------------------------------------------------------
void SpatialSort::Append( const aiVector3D* pPositions, unsigned int pNumPositions, 
	unsigned int pElementOffset,
	bool pFinalize /*= true */)
{
	// store references to all given positions along with their distance to the reference plane
	const size_t initial = mPositions.size();
	mPositions.reserve(initial + (pFinalize?pNumPositions:pNumPositions*2));
	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+initial, *vec, distance));
	}

	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, 
	float pRadius, std::vector<unsigned int>& poResults) const
{
	const float dist = pPosition * mPlaneNormal;
	const 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 = (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 aray
	std::vector<Entry>::const_iterator it = mPositions.begin() + index;
	const float 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
}

// ------------------------------------------------------------------------------------------------
unsigned int SpatialSort::GenerateMappingTable(std::vector<unsigned int>& fill,float pRadius) const
{
	fill.resize(mPositions.size(),0xffffffff);
	float dist, maxDist;

	unsigned int t=0;
	const float pSquared = pRadius*pRadius;
	for (size_t i = 0; i < mPositions.size();) {
		dist = mPositions[i].mPosition * 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 _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;
}