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Commit b13d4773 authored by Okan Arikan's avatar Okan Arikan Committed by Alex Vakulenko
Browse files

Fix pose predictor jank. 

There were two issues:
- A math error in angular velocity computation.
  This has unit tests and they were failing.
  Need to make sure these units tests get executed.

- There is an inherent sensor latency that we need to account for.

Bug: 36693596, 36196200
Test: Run VrHome, see less hanky result.
Change-Id: Ifcf191f16de9ee64aa14bcbb74c9126db18ebaa8
parent c428826f

libs/vr/libposepredictor/include/polynomial_predictor.h

+1 −1
Original line number Diff line number Diff line
@@ -19,7 +19,7 @@ class PolynomialPosePredictor : public BufferedPredictor { 
 public:

  PolynomialPosePredictor(real regularization = 1e-9)

      : BufferedPredictor(TrainingWindow), regularization_(regularization) {

    static_assert(PolynomialDegree + 1 >= TrainingWindow,

    static_assert(TrainingWindow >= PolynomialDegree + 1,

                  "Underconstrained polynomial regressor");

  }

libs/vr/libposepredictor/predictor.cpp

+1 −1
Original line number Diff line number Diff line
@@ -5,7 +5,7 @@ 
namespace posepredictor {



vec3 Predictor::AngularVelocity(const quat& a, const quat& b, real delta_time) {

  const auto delta_q = b.inverse() * a;

  const auto delta_q = a.inverse() * b;

  // Check that delta_q.w() == 1, Eigen doesn't respect this convention. If

  // delta_q.w() == -1, we'll get the opposite velocity.

  return 2.0 * (delta_q.w() < 0 ? static_cast<vec3>(-delta_q.vec()) : delta_q.vec()) / delta_time;

libs/vr/libvrsensor/Android.bp

+1 −0
Original line number Diff line number Diff line
@@ -15,6 +15,7 @@ 
sourceFiles = [

    "pose_client.cpp",

    "sensor_client.cpp",

    "latency_model.cpp",

]



includeFiles = [

libs/vr/libvrsensor/include/private/dvr/latency_model.h

0 → 100644
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#ifndef ANDROID_DVR_LATENCY_MODEL_H_

#define ANDROID_DVR_LATENCY_MODEL_H_



#include <vector>



namespace android {

namespace dvr {



// This class holds a rolling average of the sensor latency.

class LatencyModel {

 public:

  LatencyModel(size_t window_size, double weight_mass_in_window);

  ~LatencyModel() = default;



  void AddLatency(int64_t latency_ns);

  int64_t CurrentLatencyEstimate() const {

    return static_cast<int64_t>(rolling_average_);

  }



 private:

  // The rolling average of the latencies.

  double rolling_average_ = 0;



  // The alpha parameter for an exponential moving average.

  double alpha_;

};



}  // namespace dvr

}  // namespace android



#endif  // ANDROID_DVR_LATENCY_MODEL_H_

libs/vr/libvrsensor/latency_model.cpp

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#include <private/dvr/latency_model.h>



#include <cmath>



namespace android {

namespace dvr {



LatencyModel::LatencyModel(size_t window_size, double weight_mass_in_window) {

  // Compute an alpha so the weight of the last window_size measurements is

  // weight_mass_in_window of the total weights.



  // The weight in a series of k measurements:

  // alpha + (1 + (1 - alpha) + (1 - alpha)^2 + ... (1 - alpha)^k-1)

  // = alpha x (1 - (1 - alpha) ^ k) / alpha

  // = 1 - (1 - alpha) ^ k

  // weight_mass_in_window = 1 - (1 - alpha) ^ k / lim_k->inf (1 - alpha) ^ k

  // weight_mass_in_window = 1 - (1 - alpha) ^ k / 1

  // 1 - weight_mass_in_window = (1 - alpha) ^ k

  // log(1 - weight_mass_in_window) = k * log(1 - alpha)

  // 10 ^ (log(1 - weight_mass_in_window) / k) = 1 - alpha

  // alpha = 1 - 10 ^ (log(1 - weight_mass_in_window) / k)

  // alpha = 1 - 10 ^ (log(1 - weight_mass_in_window) / window_size)



  alpha_ = 1 - std::pow(10.0, std::log10(1 - weight_mass_in_window) /

                                  static_cast<double>(window_size));

}



void LatencyModel::AddLatency(int64_t latency_ns) {

  rolling_average_ = latency_ns * alpha_ + rolling_average_ * (1 - alpha_);

}



}  // namespace dvr

}  // namespace android