| OLD | NEW |
|---|
| (Empty) |
| 1 // Copyright (c) 2012 The Chromium Authors. All rights reserved. | |
| 2 // Use of this source code is governed by a BSD-style license that can be | |
| 3 // found in the LICENSE file. | |
| 4 | |
| 5 #include "ui/events/gestures/velocity_calculator.h" | |
| 6 | |
| 7 namespace ui { | |
| 8 | |
| 9 VelocityCalculator::VelocityCalculator(int buffer_size) | |
| 10 : buffer_(new Point[buffer_size]) , | |
| 11 index_(0), | |
| 12 num_valid_entries_(0), | |
| 13 buffer_size_(buffer_size), | |
| 14 x_velocity_(0), | |
| 15 y_velocity_(0), | |
| 16 velocities_stale_(false) { | |
| 17 } | |
| 18 | |
| 19 VelocityCalculator::~VelocityCalculator() {} | |
| 20 | |
| 21 float VelocityCalculator::XVelocity() { | |
| 22 if (velocities_stale_) | |
| 23 UpdateVelocity(); | |
| 24 return x_velocity_; | |
| 25 } | |
| 26 | |
| 27 float VelocityCalculator::YVelocity() { | |
| 28 if (velocities_stale_) | |
| 29 UpdateVelocity(); | |
| 30 return y_velocity_; | |
| 31 } | |
| 32 | |
| 33 void VelocityCalculator::PointSeen(float x, float y, int64 time) { | |
| 34 buffer_[index_].x = x; | |
| 35 buffer_[index_].y = y; | |
| 36 buffer_[index_].time = time; | |
| 37 | |
| 38 index_ = (index_ + 1) % buffer_size_; | |
| 39 if (num_valid_entries_ < buffer_size_) | |
| 40 ++num_valid_entries_; | |
| 41 | |
| 42 velocities_stale_ = true; | |
| 43 } | |
| 44 | |
| 45 float VelocityCalculator::VelocitySquared() { | |
| 46 if (velocities_stale_) | |
| 47 UpdateVelocity(); | |
| 48 return x_velocity_ * x_velocity_ + y_velocity_ * y_velocity_; | |
| 49 } | |
| 50 | |
| 51 void VelocityCalculator::UpdateVelocity() { | |
| 52 // We don't have enough data to make a good estimate of the velocity. | |
| 53 if (num_valid_entries_ < 2) | |
| 54 return; | |
| 55 | |
| 56 // Where A_i = A[i] - mean(A) | |
| 57 // x velocity = sum_i(x_i * t_i) / sum_i(t_i * t_i) | |
| 58 // This is an Ordinary Least Squares Regression. | |
| 59 | |
| 60 float mean_x = 0; | |
| 61 float mean_y = 0; | |
| 62 int64 mean_time = 0; | |
| 63 | |
| 64 for (size_t i = 0; i < num_valid_entries_; ++i) { | |
| 65 mean_x += buffer_[i].x; | |
| 66 mean_y += buffer_[i].y; | |
| 67 mean_time += buffer_[i].time; | |
| 68 } | |
| 69 | |
| 70 // Minimize number of divides. | |
| 71 const float num_valid_entries_i = 1.0f / num_valid_entries_; | |
| 72 | |
| 73 mean_x *= num_valid_entries_i; | |
| 74 mean_y *= num_valid_entries_i; | |
| 75 | |
| 76 // The loss in accuracy due to rounding is insignificant compared to | |
| 77 // the error due to the resolution of the timer. | |
| 78 // Use integer division to avoid the cast to double, which would cause | |
| 79 // VelocityCalculatorTest.IsAccurateWithLargeTimes to fail. | |
| 80 mean_time /= num_valid_entries_; | |
| 81 | |
| 82 float xt = 0; // sum_i(x_i * t_i) | |
| 83 float yt = 0; // sum_i(y_i * t_i) | |
| 84 int64 tt = 0; // sum_i(t_i * t_i) | |
| 85 | |
| 86 int64 t_i; | |
| 87 | |
| 88 for (size_t i = 0; i < num_valid_entries_; ++i) { | |
| 89 t_i = (buffer_[i].time - mean_time); | |
| 90 xt += (buffer_[i].x - mean_x) * t_i; | |
| 91 yt += (buffer_[i].y - mean_y) * t_i; | |
| 92 tt += t_i * t_i; | |
| 93 } | |
| 94 | |
| 95 if (tt > 0) { | |
| 96 // Convert time from microseconds to seconds. | |
| 97 x_velocity_ = xt / (tt / 1000000.0f); | |
| 98 y_velocity_ = yt / (tt / 1000000.0f); | |
| 99 } else { | |
| 100 x_velocity_ = 0.0f; | |
| 101 y_velocity_ = 0.0f; | |
| 102 } | |
| 103 velocities_stale_ = false; | |
| 104 } | |
| 105 | |
| 106 void VelocityCalculator::ClearHistory() { | |
| 107 index_ = 0; | |
| 108 num_valid_entries_ = 0; | |
| 109 x_velocity_ = 0; | |
| 110 y_velocity_ = 0; | |
| 111 velocities_stale_ = false; | |
| 112 } | |
| 113 | |
| 114 } // namespace ui | |
| OLD | NEW |
|---|
Chromium Code Reviews
Issue 458363002:
Remove old Aura Gesture Detection Pipeline. (Closed)
Base URL: svn://svn.chromium.org/chrome/trunk/src