Tried to make DOD octree. Dropped this idea.

DrawableProcessor.h

struct FlatOctant
{
    static const unsigned NUM_OCTANTS = 8;
    IntVector3 index_;
    BoundingBox boundingBox_;
    SceneProcessorDrawableSoA data_;
    Vector<FlatOctant> children_;
    unsigned numActiveChildren_ = 0;
    bool HasChildren() const { return data_.size_ == 0; }
    bool IsSubdivided() const { return !children_.Empty(); }
    void Subdivide()
    {
        const Vector3 center = boundingBox_.Center();
        children_.Resize(NUM_OCTANTS);
        for (unsigned i = 0; i < NUM_OCTANTS; ++i)
        {
            FlatOctant& child = children_[i];
            child.index_ = IntVector3(i & 1u, i & 2u, i & 4u);
            child.boundingBox_.min_ = boundingBox_.min_;
            child.boundingBox_.max_ = boundingBox_.max_;

            if (child.index_.x_)
                child.boundingBox_.min_.x_ = center.x_;
            else
                child.boundingBox_.max_.x_ = center.x_;

            if (child.index_.y_)
                child.boundingBox_.min_.y_ = center.y_;
            else
                child.boundingBox_.max_.y_ = center.y_;

            if (child.index_.z_)
                child.boundingBox_.min_.z_ = center.z_;
            else
                child.boundingBox_.max_.z_ = center.z_;
        }
    }
    void Rebalance(unsigned threshold, Vector<bool>& tempObjectsMask)
    {
        const unsigned effectiveThreshold = (threshold * (NUM_OCTANTS - numActiveChildren_) - 1) / NUM_OCTANTS + 1;
        Rebalance(effectiveThreshold, threshold / NUM_OCTANTS, threshold / NUM_OCTANTS / 2, tempObjectsMask);
    }
    void Rebalance(unsigned subdivisionThreshold, unsigned childCreationThreshold, unsigned childCollapseThreshold,
        Vector<bool>& tempObjectsMask)
    {
        if (data_.size_ < subdivisionThreshold || numActiveChildren_ == NUM_OCTANTS)
            return;

        // Subdivide if needed
        if (!IsSubdivided())
            Subdivide();

        // For each chunk, check whether to collapse
        tempObjectsMask.Resize(data_.size_);
        for (unsigned i = 0; i < NUM_OCTANTS; ++i)
        {
            // Skip already initialized children
            FlatOctant& child = children_[i];
            if (child.HasChildren())
                continue;

            for ()
            {
            }
        }
    }
    bool IsInside(const BoundingBox& boundingBox) const
    {
        return boundingBox_.IsInsideFast(boundingBox) == INSIDE;
    }
};

class FlatOctree
{
public:
    void Reset(float rootOctantSize, const BoundingBox& volume)
    {
        rootOctantSize_ = rootOctantSize;
        const IntVector3 beginOctant = VectorCeilToInt(volume.min_ / rootOctantSize_);
        const IntVector3 endOctant = VectorCeilToInt(volume.max_ / rootOctantSize_);
        const IntVector3 numOctants3 = endOctant - beginOctant + IntVector3::ONE;
        const unsigned numOctants = static_cast<unsigned>(numOctants3.x_ * numOctants3.y_ * numOctants3.z_);

        // Initialize octants
        rootOctants_.Resize(numOctants);
        unsigned index = 0;
        for (int x = beginOctant.x_; x <= endOctant.x_; ++x)
        {
            for (int y = beginOctant.y_; y <= endOctant.y_; ++y)
            {
                for (int z = beginOctant.z_; z <= endOctant.z_; ++z)
                {
                    FlatOctant& octant = rootOctants_[index];
                    octant.index_ = IntVector3(x, y, z);
                    octant.boundingBox_.min_ = Vector3(x, y, z) * rootOctantSize_;
                    octant.boundingBox_.max_ = octant.boundingBox_.min_ + Vector3::ONE * rootOctantSize_;
                    ++index;
                }
            }
        }
    }
    /// Update or add drawable.
    void UpdateDrawable(Drawable* drawable)
    {
        const BoundingBox& boundingBox = drawable->GetWorldBoundingBox();
    }
private:
    float rootOctantSize_;
    FlatOctant defaultOctant_;
    Vector<FlatOctant> rootOctants_;
};