Method merge

openpgl/data/SampleStatistics.h:130–165

    }

    void merge(const SampleStatistics &b)
    {
        if (numSamples + b.numSamples == 0)
        {
            return;
        }

        const Point3 meanA = mean;
        const Point3 meanB = b.mean;

        const Vector3 varianceA = variance;
        const Vector3 varianceB = b.variance;

        const float numSamplesA = numSamples;
        const float numSamplesB = b.numSamples;

        const float weightA = numSamplesA / (numSamplesA + numSamplesB);
        const float weightB = 1.0f - weightA;
        mean = meanA * weightA + meanB * weightB;
        numSamples += numSamplesB;

        // Simple version to calculate the variance of two merged distributions
        // variance = (weightA * (varianceA + meanA * meanA) + weightB * (varianceB + meanB * meanB)) - (mean * mean);
        // Numerical more stable version to calculate the variance of two merged distributions
        const Point3 meanDiffA = meanA - mean;
        const Point3 meanDiffB = meanB - mean;
        variance = (weightA * varianceA + weightB * varianceB) + (weightA * (meanDiffA * meanDiffA) + weightB * (meanDiffB * meanDiffB));
        variance.x = variance.x >= 0.f ? variance.x : 0.f;
        variance.y = variance.y >= 0.f ? variance.y : 0.f;
        variance.z = variance.z >= 0.f ? variance.z : 0.f;
        sampleBounds.extend(b.sampleBounds);

        numZeroValueSamples += b.numZeroValueSamples;

        OPENPGL_ASSERT(isValid());
    }

    inline bool isValid() const
    {