Function orb

src/backend/cpu/orb.cpp:44–283

template<typename T, typename convAccT>
unsigned orb(Array<float>& x, Array<float>& y, Array<float>& score,
             Array<float>& ori, Array<float>& size, Array<uint>& desc,
             const Array<T>& image, const float fast_thr,
             const unsigned max_feat, const float scl_fctr,
             const unsigned levels, const bool blur_img) {
    image.eval();
    getQueue().sync();

    float patch_size = REF_PAT_SIZE;

    const dim4& idims   = image.dims();
    float min_side      = min(idims[0], idims[1]);
    unsigned max_levels = 0;
    float scl_sum       = 0.f;

    for (unsigned i = 0; i < levels; i++) {
        min_side /= scl_fctr;

        // Minimum image side for a descriptor to be computed
        if (min_side < patch_size || max_levels == levels) { break; }

        max_levels++;
        scl_sum += 1.f / pow(scl_fctr, static_cast<float>(i));
    }

    vector<unique_ptr<float[], function<void(float*)>>> h_x_pyr(max_levels);
    vector<unique_ptr<float[], function<void(float*)>>> h_y_pyr(max_levels);
    vector<unique_ptr<float[], function<void(float*)>>> h_score_pyr(max_levels);
    vector<unique_ptr<float[], function<void(float*)>>> h_ori_pyr(max_levels);
    vector<unique_ptr<float[], function<void(float*)>>> h_size_pyr(max_levels);
    vector<unique_ptr<unsigned[], function<void(unsigned*)>>> h_desc_pyr(
        max_levels);

    vector<unsigned> feat_pyr(max_levels);
    unsigned total_feat = 0;

    // Compute number of features to keep for each level
    vector<unsigned> lvl_best(max_levels);
    unsigned feat_sum = 0;
    for (unsigned i = 0; i < max_levels - 1; i++) {
        auto lvl_scl = pow(scl_fctr, static_cast<float>(i));
        lvl_best[i]  = ceil((static_cast<float>(max_feat) / scl_sum) / lvl_scl);
        feat_sum += lvl_best[i];
    }
    lvl_best[max_levels - 1] = max_feat - feat_sum;

    // Maintain a reference to previous level image
    Array<T> prev_img = createEmptyArray<T>(dim4());
    dim4 prev_ldims;

    dim4 gauss_dims(9);
    unique_ptr<T[], function<void(T*)>> h_gauss;
    Array<T> gauss_filter = createEmptyArray<T>(dim4());

    for (unsigned i = 0; i < max_levels; i++) {
        dim4 ldims;
        const auto lvl_scl = pow(scl_fctr, static_cast<float>(i));
        Array<T> lvl_img   = createEmptyArray<T>(dim4());