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mediapipe/mediapipe/util/tracking/region_flow.cc
MediaPipe Team 350fbb2100 Project import generated by Copybara. 
GitOrigin-RevId: d073f8e21be2fcc0e503cb97c6695078b6b75310
2021-02-27 03:30:05 -05:00

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// Copyright 2019 The MediaPipe Authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
#include "mediapipe/util/tracking/region_flow.h"
#include <stddef.h>
#include <cmath>
#include <memory>
#include <numeric>
#include "absl/container/node_hash_map.h"
#include "absl/container/node_hash_set.h"
#include "absl/strings/str_cat.h"
#include "mediapipe/framework/port/integral_types.h"
#include "mediapipe/util/tracking/measure_time.h"
#include "mediapipe/util/tracking/parallel_invoker.h"
namespace mediapipe {
namespace {
bool IsPointWithinBounds(const Vector2_f& pt, float bounds, int frame_width,
int frame_height) {
// Ensure stability under float -> rounding operations.
if (pt.x() - 0.5f >= bounds && pt.x() + 0.5f <= frame_width - 1 - bounds &&
pt.y() - 0.5f >= bounds && pt.y() + 0.5f <= frame_height - 1 - bounds) {
return true;
} else {
return false;
}
}
} // namespace.
void GetRegionFlowFeatureList(const RegionFlowFrame& region_flow_frame,
int distance_from_border,
RegionFlowFeatureList* flow_feature_list) {
CHECK(flow_feature_list);
flow_feature_list->clear_feature();
const int frame_width = region_flow_frame.frame_width();
const int frame_height = region_flow_frame.frame_height();
flow_feature_list->set_frame_width(frame_width);
flow_feature_list->set_frame_height(frame_height);
flow_feature_list->set_unstable(region_flow_frame.unstable_frame());
flow_feature_list->set_distance_from_border(distance_from_border);
flow_feature_list->set_blur_score(region_flow_frame.blur_score());
for (const auto& region_flow : region_flow_frame.region_flow()) {
for (const auto& feature : region_flow.feature()) {
if (distance_from_border > 0) {
if (!IsPointWithinBounds(FeatureLocation(feature), distance_from_border,
frame_width, frame_height) ||
!IsPointWithinBounds(FeatureMatchLocation(feature),
distance_from_border, frame_width,
frame_height)) {
continue;
}
}
flow_feature_list->add_feature()->CopyFrom(feature);
}
}
}
float RegionFlowFeatureDistance(const PatchDescriptor& patch_desc_1,
const PatchDescriptor& patch_desc_2) {
DCHECK_EQ(patch_desc_1.data_size(), patch_desc_2.data_size());
DCHECK_GE(patch_desc_1.data_size(), 3);
constexpr int kNumMeans = 3;
float sq_distance_sum = 0;
for (int n = 0; n < kNumMeans; ++n) {
const float distance = patch_desc_1.data(n) - patch_desc_2.data(n);
sq_distance_sum += distance * distance;
}
return std::sqrt(sq_distance_sum);
}
void ResetRegionFlowFeatureIRLSWeights(
float value, RegionFlowFeatureList* flow_feature_list) {
for (auto& feature : *flow_feature_list->mutable_feature()) {
feature.set_irls_weight(value);
}
}
double RegionFlowFeatureIRLSSum(const RegionFlowFeatureList& feature_list) {
double sum = 0.0;
for (const auto& feature : feature_list.feature()) {
sum += feature.irls_weight();
}
return sum;
}
void ClampRegionFlowFeatureIRLSWeights(float lower, float upper,
RegionFlowFeatureView* feature_view) {
for (auto& feature_ptr : *feature_view) {
if (feature_ptr->irls_weight() < lower) {
feature_ptr->set_irls_weight(lower);
} else if (feature_ptr->irls_weight() > upper) {
feature_ptr->set_irls_weight(upper);
}
}
}
void ComputeRegionFlowFeatureTexturedness(
const RegionFlowFeatureList& flow_feature_list, bool use_15percent_as_max,
std::vector<float>* texturedness) {
CHECK(texturedness != nullptr);
*texturedness = std::vector<float>(flow_feature_list.feature_size(), 1.0f);
int texture_idx = 0;
for (auto feature = flow_feature_list.feature().begin();
feature != flow_feature_list.feature().end(); ++feature, ++texture_idx) {
const float feature_stdev_l1 =
PatchDescriptorColorStdevL1(feature->feature_descriptor());
if (feature_stdev_l1 < 0.0f) {
LOG_IF(WARNING,
[]() {
static int k = 0;
return k++ < 2;
}())
<< "Feature descriptor does not contain variance information. Was "
<< "ComputeRegionFlowFeatureDescriptors called?";
continue;
}
// feature_stdev_l1 is within [0, 3 * 128 = 384]
float alpha = feature_stdev_l1 / 384.f;
// In [0, 1], 0 = low texture, 1 = high texture. Scale such that around
// 15% of per channel maximum stdev is considered totally textured
// (1 / 0.15 * 3 ~ 18);
if (use_15percent_as_max) {
alpha = std::min(1.0f, alpha * 18.f);
}
(*texturedness)[texture_idx] = alpha;
}
}
void TextureFilteredRegionFlowFeatureIRLSWeights(
float low_texture_threshold, float low_texture_outlier_clamp,
RegionFlowFeatureList* flow_feature_list) {
std::vector<float> texturedness;
ComputeRegionFlowFeatureTexturedness(*flow_feature_list, true, &texturedness);
int texture_idx = 0;
for (auto feature = flow_feature_list->mutable_feature()->begin();
feature != flow_feature_list->mutable_feature()->end();
++feature, ++texture_idx) {
if (feature->irls_weight() == 0.0f) {
continue;
}
if (texturedness[texture_idx] < low_texture_threshold &&
feature->irls_weight() < low_texture_outlier_clamp) {
feature->set_irls_weight(low_texture_outlier_clamp);
} else {
feature->set_irls_weight(feature->irls_weight() /
(texturedness[texture_idx] + 1.e-6f));
}
}
}
void CornerFilteredRegionFlowFeatureIRLSWeights(
float low_corner_threshold, float low_corner_outlier_clamp,
RegionFlowFeatureList* flow_feature_list) {
for (auto feature = flow_feature_list->mutable_feature()->begin();
feature != flow_feature_list->mutable_feature()->end(); ++feature) {
if (feature->irls_weight() == 0.0f) {
continue;
}
const float corner_response = feature->corner_response();
if (corner_response < low_corner_threshold &&
feature->irls_weight() < low_corner_threshold) {
feature->set_irls_weight(low_corner_outlier_clamp);
} else {
feature->set_irls_weight(feature->irls_weight() /
(corner_response + 1.e-6f));
}
}
}
void GetRegionFlowFeatureIRLSWeights(
const RegionFlowFeatureList& flow_feature_list,
std::vector<float>* irls_weights) {
CHECK(irls_weights != nullptr);
irls_weights->clear();
irls_weights->reserve(flow_feature_list.feature_size());
for (auto feature = flow_feature_list.feature().begin();
feature != flow_feature_list.feature().end(); ++feature) {
irls_weights->push_back(feature->irls_weight());
}
}
void SetRegionFlowFeatureIRLSWeights(const std::vector<float>& irls_weights,
RegionFlowFeatureList* flow_feature_list) {
CHECK(flow_feature_list != nullptr);
CHECK_EQ(irls_weights.size(), flow_feature_list->feature_size());
int idx = 0;
for (auto feature = flow_feature_list->mutable_feature()->begin();
feature != flow_feature_list->mutable_feature()->end();
++feature, ++idx) {
feature->set_irls_weight(irls_weights[idx]);
}
}
int CountIgnoredRegionFlowFeatures(
const RegionFlowFeatureList& flow_feature_list, float threshold) {
int count = 0;
for (auto feature = flow_feature_list.feature().begin();
feature != flow_feature_list.feature().end(); ++feature) {
if (feature->irls_weight() <= threshold) {
++count;
}
}
return count;
}
namespace {
struct RegionFlowLocator {
bool operator()(const RegionFlow& lhs, const RegionFlow& rhs) const {
return lhs.region_id() < rhs.region_id();
}
};
} // namespace.
const RegionFlow* GetRegionFlowById(int region_id,
const RegionFlowFrame& flow_frame) {
RegionFlow region_flow;
region_flow.set_region_id(region_id);
const auto& region_pos = std::lower_bound(flow_frame.region_flow().begin(),
flow_frame.region_flow().end(),
region_flow, RegionFlowLocator());
if (region_pos == flow_frame.region_flow().end() ||
region_pos->region_id() != region_id) {
return NULL;
} else {
return &(*region_pos);
}
}
RegionFlow* GetMutableRegionFlowById(int region_id,
RegionFlowFrame* flow_frame) {
RegionFlow region_flow;
region_flow.set_region_id(region_id);
auto region_pos = std::lower_bound(flow_frame->mutable_region_flow()->begin(),
flow_frame->mutable_region_flow()->end(),
region_flow, RegionFlowLocator());
if (region_pos == flow_frame->mutable_region_flow()->end() ||
region_pos->region_id() != region_id) {
return NULL;
} else {
return &(*region_pos);
}
}
void SortRegionFlowById(RegionFlowFrame* flow_frame) {
std::sort(flow_frame->mutable_region_flow()->begin(),
flow_frame->mutable_region_flow()->end(), RegionFlowLocator());
}
void InvertRegionFlow(const RegionFlowFrame& region_flow_frame,
RegionFlowFrame* inverted_flow_frame) {
CHECK(inverted_flow_frame);
inverted_flow_frame->CopyFrom(region_flow_frame);
for (auto& region_flow : *inverted_flow_frame->mutable_region_flow()) {
region_flow.set_centroid_x(region_flow.centroid_x() + region_flow.flow_x());
region_flow.set_centroid_y(region_flow.centroid_y() + region_flow.flow_y());
region_flow.set_flow_x(-region_flow.flow_x());
region_flow.set_flow_y(-region_flow.flow_y());
for (auto& feature : *region_flow.mutable_feature()) {
feature.set_x(feature.x() + feature.dx());
feature.set_y(feature.y() + feature.dy());
feature.set_dx(-feature.dx());
feature.set_dy(-feature.dy());
}
}
}
void InvertRegionFlowFeatureList(const RegionFlowFeatureList& feature_list,
RegionFlowFeatureList* inverted_feature_list) {
CHECK(inverted_feature_list);
*inverted_feature_list = feature_list;
for (auto& feature : *inverted_feature_list->mutable_feature()) {
InvertRegionFlowFeature(&feature);
}
}
void InvertRegionFlowFeature(RegionFlowFeature* feature) {
Vector2_f pt_match = FeatureMatchLocation(*feature);
feature->set_x(pt_match.x());
feature->set_y(pt_match.y());
Vector2_f flow = FeatureFlow(*feature);
feature->set_dx(-flow.x());
feature->set_dy(-flow.y());
}
void LimitFeaturesToBounds(int frame_width, int frame_height, float bounds,
RegionFlowFeatureList* feature_list) {
RegionFlowFeatureList limited;
for (const auto& feature : feature_list->feature()) {
if (!IsPointWithinBounds(FeatureLocation(feature), bounds, frame_width,
frame_height)) {
continue;
} else {
limited.add_feature()->CopyFrom(feature);
}
}
feature_list->Swap(&limited);
}
void NormalizeRegionFlowFeatureList(RegionFlowFeatureList* feature_list) {
const LinearSimilarityModel norm_model =
LinearSimilarityAdapter::NormalizationTransform(
feature_list->frame_width(), feature_list->frame_height());
TransformRegionFlowFeatureList(norm_model, feature_list);
}
void DeNormalizeRegionFlowFeatureList(RegionFlowFeatureList* feature_list) {
const LinearSimilarityModel norm_model =
LinearSimilarityAdapter::NormalizationTransform(
feature_list->frame_width(), feature_list->frame_height());
TransformRegionFlowFeatureList(ModelInvert(norm_model), feature_list);
}
void ScaleSalientPoint(float scale_x, float scale_y, SalientPoint* sp) {
sp->set_norm_point_x(sp->norm_point_x() * scale_x);
sp->set_norm_point_y(sp->norm_point_y() * scale_y);
const float cos_angle = std::cos(sp->angle());
const float sin_angle = std::sin(sp->angle());
Vector2_f major_axis = Vector2_f(cos_angle, sin_angle) * sp->norm_major();
Vector2_f minor_axis = Vector2_f(-sin_angle, cos_angle) * sp->norm_minor();
major_axis[0] *= scale_x;
major_axis[1] *= scale_y;
minor_axis[0] *= scale_x;
minor_axis[1] *= scale_y;
sp->set_norm_major(major_axis.Norm());
sp->set_norm_minor(minor_axis.Norm());
sp->set_angle(std::atan2(major_axis.y(), major_axis.x()));
if (sp->angle() < 0) {
sp->set_angle(sp->angle() + M_PI);
}
}
void ScaleSaliencyList(float scale, bool normalize_to_scale,
SaliencyPointList* saliency_list) {
CHECK(saliency_list != nullptr);
for (auto& point_frame : *saliency_list) {
ScaleSalientPointFrame(scale, normalize_to_scale, &point_frame);
}
}
void ScaleSalientPointFrame(float scale, bool normalize_to_scale,
SalientPointFrame* saliency) {
CHECK(saliency != nullptr);
float saliency_scale = scale;
if (normalize_to_scale) {
float weight_sum = 0.0f;
for (const auto& salient_point : saliency->point()) {
weight_sum += salient_point.weight();
}
if (weight_sum > 1e-6f) {
saliency_scale /= weight_sum;
}
}
for (auto& salient_point : *saliency->mutable_point()) {
salient_point.set_weight(salient_point.weight() * saliency_scale);
}
}
void ResetSaliencyBounds(float left, float bottom, float right, float top,
SaliencyPointList* saliency_list) {
CHECK(saliency_list != nullptr);
for (auto& point_frame : *saliency_list) {
for (auto& salient_point : *point_frame.mutable_point()) {
salient_point.set_left(left);
salient_point.set_bottom(bottom);
salient_point.set_right(right);
salient_point.set_top(top);
}
}
}
bool EllipseFromCovariance(float a, float bc, float d,
Vector2_f* axis_magnitude, float* angle) {
CHECK(axis_magnitude != nullptr);
CHECK(angle != nullptr);
// Get trace and determinant
const float trace = a + d;
const float det = a * d - bc * bc;
// If area is very small (small axis in at least one direction)
// axis are unreliable -> return false.
if (det < 4) { // Measured in sq. pixels.
*axis_magnitude = Vector2_f(1, 1);
*angle = 0;
return false;
}
const float discriminant = std::max(0.f, trace * trace * 0.25f - det);
const float sqrt_discrm = std::sqrt(discriminant);
// Get eigenvalues.
float eig_1 = trace * 0.5f + sqrt_discrm;
float eig_2 = trace * 0.5f - sqrt_discrm;
// Compute eigenvectors.
Vector2_f vec_1, vec_2;
if (fabs(bc) < 1e-6) {
// Right-most case, we already have diagonal matrix.
vec_1.Set(1, 0);
vec_2.Set(0, 1);
} else {
vec_1.Set(eig_1 - d, bc);
vec_2.Set(eig_2 - d, bc);
// Normalize. Norm is always > 0, as bc is > 0 via above if.
vec_1 /= vec_1.Norm();
vec_2 /= vec_2.Norm();
}
// Select positive eigenvector.
if (eig_1 < 0) {
eig_1 *= -1.f;
}
if (eig_2 < 0) {
eig_2 *= -1.f;
}
// Major first.
if (eig_1 < eig_2) {
using std::swap;
swap(vec_1, vec_2);
swap(eig_1, eig_2);
}
*axis_magnitude = Vector2_f(std::sqrt(eig_1), std::sqrt(eig_2));
*angle = std::atan2(vec_1.y(), vec_1.x());
return eig_2 >= 1.5f; // Measurement in pixels.
}
void BoundingBoxFromEllipse(const Vector2_f& center, float norm_major_axis,
float norm_minor_axis, float angle,
std::vector<Vector2_f>* bounding_box) {
CHECK(bounding_box != nullptr);
float dim_x;
float dim_y;
if (angle < M_PI * 0.25 || angle > M_PI * 0.75) {
dim_x = norm_major_axis;
dim_y = norm_minor_axis;
} else {
dim_y = norm_major_axis;
dim_x = norm_minor_axis;
}
// Construct bounding for for axes aligned ellipse.
*bounding_box = {
Vector2_f(-dim_x, -dim_y),
Vector2_f(-dim_x, dim_y),
Vector2_f(dim_x, dim_y),
Vector2_f(dim_x, -dim_y),
};
for (Vector2_f& corner : *bounding_box) {
corner += center;
}
}
void CopyToEmptyFeatureList(RegionFlowFeatureList* src,
RegionFlowFeatureList* dst) {
CHECK(src != nullptr);
CHECK(dst != nullptr);
// Swap out features for empty list.
RegionFlowFeatureList empty_list;
empty_list.mutable_feature()->Swap(src->mutable_feature());
// Copy.
dst->CopyFrom(*src);
// Swap back.
src->mutable_feature()->Swap(empty_list.mutable_feature());
// src_features should be empty as in the beginning.
CHECK_EQ(0, empty_list.feature_size());
}
void IntersectRegionFlowFeatureList(
const RegionFlowFeatureList& to,
std::function<Vector2_f(const RegionFlowFeature&)> to_location_eval,
RegionFlowFeatureList* from, RegionFlowFeatureList* result,
std::vector<int>* source_indices) {
CHECK(from != nullptr);
CHECK(result != nullptr);
CHECK(from->long_tracks()) << "Intersection only works for long features";
CHECK(to.long_tracks()) << "Intersection only works for long features";
// Hash features in to, based on track_id.
absl::node_hash_map<int, const RegionFlowFeature*> track_map;
for (const auto& feature : to.feature()) {
track_map[feature.track_id()] = &feature;
}
// Initialize result.
CopyToEmptyFeatureList(from, result);
const int num_from_features = from->feature_size();
result->mutable_feature()->Reserve(num_from_features);
int feature_idx = 0;
for (const auto& feature : from->feature()) {
auto find_location = track_map.find(feature.track_id());
if (find_location != track_map.end()) {
const Vector2_f diff =
to_location_eval(*find_location->second) - FeatureLocation(feature);
RegionFlowFeature* new_feature = result->add_feature();
new_feature->CopyFrom(feature);
new_feature->set_dx(diff.x());
new_feature->set_dy(diff.y());
if (source_indices != nullptr) {
source_indices->push_back(feature_idx);
}
}
++feature_idx;
}
}
void LongFeatureStream::AddFeatures(const RegionFlowFeatureList& feature_list,
bool check_connectivity,
bool purge_non_present_features) {
if (!feature_list.long_tracks()) {
LOG(ERROR) << "Feature stream should be used only used with long feature "
<< "tracks. Ensure POLICY_LONG_FEATURE was used for "
<< "RegionFlowComputation.";
return;
}
if (feature_list.match_frame() == 0) {
// Skip first frame.
return;
}
if (std::abs(feature_list.match_frame()) != 1) {
LOG(ERROR) << "Only matching frames one frame from current one are "
<< "supported";
return;
}
// Record id of each track that is present in the current feature_list.
absl::node_hash_set<int> present_tracks;
for (auto feature : feature_list.feature()) { // Copy feature.
if (feature.track_id() < 0) {
LOG_IF(WARNING, []() {
static int k = 0;
return k++ < 2;
}()) << "Feature does not have a valid track id assigned. Ignoring.";
continue;
}
present_tracks.insert(feature.track_id());
if (check_connectivity) {
// A new feature should never have been erased before.
CHECK(old_ids_.find(feature.track_id()) == old_ids_.end())
<< "Feature : " << feature.track_id() << "was already removed.";
}
// Invert the features to be foward or backward according to forward_ flag.
if ((!forward_ && feature_list.match_frame() > 0) ||
(forward_ && feature_list.match_frame() < 0)) {
InvertRegionFlowFeature(&feature);
}
auto find_pos = tracks_.find(feature.track_id());
if (find_pos != tracks_.end()) {
// Track is present, add to it.
if (check_connectivity) {
CHECK_LT((FeatureLocation(find_pos->second.back()) -
FeatureMatchLocation(feature))
.Norm2(),
1e-4);
}
find_pos->second.push_back(feature);
} else {
tracks_[feature.track_id()] = std::vector<RegionFlowFeature>(1, feature);
}
}
if (purge_non_present_features) {
std::vector<int> to_be_removed;
for (const auto& track : tracks_) {
if (present_tracks.find(track.first) == present_tracks.end()) {
to_be_removed.push_back(track.first);
if (check_connectivity) {
old_ids_.insert(track.first);
}
}
}
for (int id : to_be_removed) {
tracks_.erase(id);
}
}
}
void LongFeatureStream::FlattenTrack(
const std::vector<RegionFlowFeature>& features,
std::vector<Vector2_f>* result, std::vector<float>* irls_weight,
std::vector<Vector2_f>* flow) const {
CHECK(result != nullptr);
if (features.empty()) {
return;
}
if (irls_weight) {
irls_weight->clear();
}
if (flow) {
flow->clear();
}
if (!forward_) {
// Backward tracking, add first match.
result->push_back(FeatureMatchLocation(features[0]));
}
for (const auto& feature : features) {
result->push_back(FeatureLocation(feature));
if (flow) {
flow->push_back(FeatureFlow(feature));
}
if (irls_weight) {
irls_weight->push_back(feature.irls_weight());
}
}
if (forward_) {
// Forward tracking, add last match.
result->push_back(FeatureMatchLocation(features.back()));
}
// Replicate last irls weight.
if (irls_weight) {
irls_weight->push_back(irls_weight->back());
}
}
const std::vector<RegionFlowFeature>* LongFeatureStream::TrackById(
int id) const {
auto track_pos = tracks_.find(id);
if (track_pos == tracks_.end()) {
return nullptr;
} else {
return &track_pos->second;
}
}
std::vector<Vector2_f> LongFeatureStream::FlattenedTrackById(int id) const {
const auto* track = TrackById(id);
if (track != nullptr) {
std::vector<Vector2_f> points;
FlattenTrack(*track, &points, nullptr, nullptr);
return points;
} else {
return std::vector<Vector2_f>();
}
}
void LongFeatureInfo::AddFeatures(const RegionFlowFeatureList& feature_list) {
if (!feature_list.long_tracks()) {
LOG(ERROR) << "Passed feature list was not computed with long tracks. ";
return;
}
for (const auto& feature : feature_list.feature()) {
AddFeature(feature);
}
IncrementFrame();
}
void LongFeatureInfo::AddFeature(const RegionFlowFeature& feature) {
if (feature.irls_weight() == 0) { // Skip outliers.
return;
}
const int track_id = feature.track_id();
if (track_id < 0) { // Skip unassigned ids.
return;
}
auto insert_pos = track_info_.find(track_id);
if (insert_pos == track_info_.end()) {
track_info_[track_id].start = num_frames_;
track_info_[track_id].length = 1;
} else {
++insert_pos->second.length;
}
}
void LongFeatureInfo::TrackLengths(const RegionFlowFeatureList& feature_list,
std::vector<int>* track_lengths) const {
CHECK(track_lengths);
const int feature_size = feature_list.feature_size();
track_lengths->resize(feature_size);
for (int k = 0; k < feature_size; ++k) {
(*track_lengths)[k] = TrackLength(feature_list.feature(k));
}
}
int LongFeatureInfo::TrackLength(const RegionFlowFeature& feature) const {
const auto insert_pos = track_info_.find(feature.track_id());
return insert_pos != track_info_.end() ? insert_pos->second.length : 0;
}
int LongFeatureInfo::TrackStart(const RegionFlowFeature& feature) const {
const auto insert_pos = track_info_.find(feature.track_id());
return insert_pos != track_info_.end() ? insert_pos->second.start : -1;
}
void LongFeatureInfo::Reset() {
track_info_.clear();
num_frames_ = 0;
}
int LongFeatureInfo::GlobalTrackLength(float percentile) const {
std::vector<int> track_lengths;
track_lengths.reserve(track_info_.size());
for (const auto& pair : track_info_) {
track_lengths.push_back(pair.second.length);
}
if (track_lengths.empty()) {
return 0;
}
auto percentile_item =
track_lengths.begin() + percentile * track_lengths.size();
std::nth_element(track_lengths.begin(), percentile_item, track_lengths.end());
return *percentile_item;
}
void GridTaps(int dim_x, int dim_y, int tap_radius,
std::vector<std::vector<int>>* taps) {
CHECK(taps);
const int grid_size = dim_x * dim_y;
const int diam = 2 * tap_radius + 1;
taps->resize(grid_size);
for (int i = 0; i < dim_y; ++i) {
for (int j = 0; j < dim_x; ++j) {
std::vector<int>& grid_bin = (*taps)[i * dim_x + j];
grid_bin.clear();
grid_bin.reserve(diam * diam);
for (int k = std::max(0, i - tap_radius),
end_k = std::min(dim_y - 1, i + tap_radius);
k <= end_k; ++k) {
for (int l = std::max(0, j - tap_radius),
end_l = std::min(dim_x - 1, j + tap_radius);
l <= end_l; ++l) {
grid_bin.push_back(k * dim_x + l);
}
}
}
}
}
} // namespace mediapipe
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