NormalHistogram.h

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// Copyright Epic Games, Inc. All Rights Reserved.
 
#pragma once
 
#include "MathUtil.h"
#include "VectorTypes.h"
#include "Sampling/SphericalFibonacci.h"
 
namespace UE
{
namespace Geometry
{
 
using namespace UE::Math;
 
template<typename RealType>
class TNormalHistogram
{
public:
    int32 Bins;
    TSphericalFibonacci<RealType> BinPoints;
    TArray<RealType> WeightedCounts;
 
    TNormalHistogram(int32 NumBins)
    {
        Bins = NumBins;
        BinPoints = TSphericalFibonacci<RealType>(NumBins);
        WeightedCounts.Init(0, BinPoints.Num());
    }
 
    void Count(const TVector<RealType>& Normal, RealType Weight = 1)
    {
        int32 BinIndex = BinPoints.FindIndex(Normal);
        WeightedCounts[BinIndex] += Weight;
    }
 
    TVector<RealType> FindMaxNormal() const
    {
        int MaxIndex = 0;
        for (int k = 1; k < Bins; ++k)
        {
            if (WeightedCounts[k] > WeightedCounts[MaxIndex])
            {
                MaxIndex = k;
            }
        }
        return BinPoints[MaxIndex];
    }
 
 
    RealType WeightedSpreadMetric() const
    {
        int32 NumOccupiedBins = 0;
        RealType TotalWeightedCount = 0;
        for (int k = 0; k < Bins; ++k)
        {
            if (WeightedCounts[k] > 0)
            {
                TotalWeightedCount += WeightedCounts[k];
                NumOccupiedBins++;
            }
        }
 
        RealType Metric = 0;
        for (int32 k = 0; k < Bins; ++k)
        {
            if (WeightedCounts[k] > 0)
            {
                RealType MassFraction = WeightedCounts[k] / TotalWeightedCount;
                MassFraction /= (RealType)NumOccupiedBins;
                Metric += MassFraction;
            }
        }
 
        return 1.0 / Metric;
    }
};
 
 
 
} // end namespace UE::Geometry
} // end namespace UE