[On-device adaptive brightness] Implement a monotonic gaussian model.

This model is responsible to train a brightness curve.

Bug: 881215
Change-Id: Ic0c474a0c1f8db6e5f14ae6b738f4d4a1086bf4b
Reviewed-on: https://chromium-review.googlesource.com/c/1300353
Commit-Queue: Jia Meng <jiameng@chromium.org>
Reviewed-by: Andrew Moylan <amoylan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#603417}

chrome/browser/chromeos/BUILD.gn

@@ -1604,6 +1604,8 @@ source_set("chromeos") {
     "power/auto_screen_brightness/fake_als_reader.h",
     "power/auto_screen_brightness/fake_brightness_monitor.cc",
     "power/auto_screen_brightness/fake_brightness_monitor.h",
+    "power/auto_screen_brightness/gaussian_trainer.cc",
+    "power/auto_screen_brightness/gaussian_trainer.h",
     "power/auto_screen_brightness/modeller.h",
     "power/auto_screen_brightness/modeller_impl.cc",
     "power/auto_screen_brightness/modeller_impl.h",
@@ -2287,6 +2289,7 @@ source_set("unit_tests") {
     "policy/user_cloud_policy_store_chromeos_unittest.cc",
     "power/auto_screen_brightness/als_reader_impl_unittest.cc",
     "power/auto_screen_brightness/brightness_monitor_impl_unittest.cc",
+    "power/auto_screen_brightness/gaussian_trainer_unittest.cc",
     "power/auto_screen_brightness/modeller_impl_unittest.cc",
     "power/auto_screen_brightness/monotone_cubic_spline_unittest.cc",
     "power/auto_screen_brightness/utils_unittest.cc",

chrome/browser/chromeos/power/auto_screen_brightness/gaussian_trainer.h

+// Copyright 2018 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef CHROME_BROWSER_CHROMEOS_POWER_AUTO_SCREEN_BRIGHTNESS_GAUSSIAN_TRAINER_H_
+#define CHROME_BROWSER_CHROMEOS_POWER_AUTO_SCREEN_BRIGHTNESS_GAUSSIAN_TRAINER_H_
+
+#include <memory>
+
+#include "chrome/browser/chromeos/power/auto_screen_brightness/trainer.h"
+
+namespace chromeos {
+namespace power {
+namespace auto_screen_brightness {
+
+// GaussianTrainer updates an existing brightness curve (a mapping from
+// ambient light to screen brightness) using training data points that represent
+// how user changes brightness following an ambient value change. The update
+// procedure is Gaussian hence the name. It uses a global curve to check for
+// outliers that may exist in training data. It also ensures new curves are
+// monotone and also satisfy requirements on the slope.
+class GaussianTrainer : public Trainer {
+ public:
+  // TODO(jiameng): revise default values.
+  struct Params {
+    // |brightness_bound_scale| and |brightness_bound_offset| are used to define
+    // training example outliers.
+    double brightness_bound_scale = 1.5;
+    double brightness_bound_offset = 40;
+
+    // |brightness_step_size| defines reasonable brightness change scale: a
+    // reasonable change would be between
+    // brightness_old/(1+|brightness_step_size|) and
+    // brightness_old*(1+|brightness_step_size|)
+    double brightness_step_size = 0.2;
+
+    // One training data point could modify all the points on the curve, but its
+    // effect is greatest on the point nearest to it (as measured by difference
+    // in ambient value). The effect on the other points decay with a Gaussian
+    // distribution with standard deviation |sigma|.
+    double sigma = 1;
+
+    // If log lux is below |low_log_lux_threshold| then we'll use
+    // |min_grad_low_lux| as gradient constraint.
+    double low_log_lux_threshold = 0.1;
+    double min_grad_low_lux = 0;
+
+    // Min and max grad as a power of brightness ratios.
+    double min_grad = 0.25;
+    double max_grad = 1;
+
+    double min_brightness = 0;
+  };
+
+  GaussianTrainer();
+  ~GaussianTrainer() override;
+
+  // Trainer overrides:
+  void SetInitialCurves(const MonotoneCubicSpline& global_curve,
+                        const MonotoneCubicSpline& current_curve) override;
+  MonotoneCubicSpline Train(
+      const std::vector<TrainingDataPoint>& data) override;
+
+ private:
+  // Updates |brightness_| using |data|. It also sets |need_to_update_curve_|
+  // to true if |brightness_| is actually changed.
+  void AdjustCurveWithSingleDataPoint(const TrainingDataPoint& data);
+
+  // Called each time |AdjustCurveWithSingleDataPoint| changes |brightness_|.
+  // It ensures the curve is still monotone and also satisfies min/max grad
+  // constraints. It does this by changing points to the left and to the right
+  // of |center_index|.
+  void EnforceMonotonicity(size_t center_index);
+
+  Params params_;
+  // |global_curve| does not change after |SetInitialCurves| is called.
+  base::Optional<MonotoneCubicSpline> global_curve_;
+  // |current_curve_| initially is set by |SetInitialCurves| and then gets
+  // updated during training.
+  base::Optional<MonotoneCubicSpline> current_curve_;
+
+  // Whether the |brightness_| has been updated since last time |Train| updated
+  // the curve.
+  bool need_to_update_curve_ = false;
+
+  // (|ambient_log_lux_|, |brightness_|) are the control points of
+  // |current_curve_|. |ambient_log_lux_| doesn't change, but |brightness_| may
+  // be updated during training.
+  std::vector<double> ambient_log_lux_;
+  std::vector<double> brightness_;
+
+  // Minimum and max brightness ratios of two adjacent control points. They are
+  // calculated from the global curve's brightness values.
+  std::vector<double> min_ratios_;
+  std::vector<double> max_ratios_;
+
+  DISALLOW_COPY_AND_ASSIGN(GaussianTrainer);
+};
+
+}  // namespace auto_screen_brightness
+}  // namespace power
+}  // namespace chromeos
+
+#endif  // CHROME_BROWSER_CHROMEOS_POWER_AUTO_SCREEN_BRIGHTNESS_GAUSSIAN_TRAINER_H_

chromeos/chromeos_features.cc

@@ -16,6 +16,11 @@ const base::Feature kAndroidMessagesIntegration{
 const base::Feature kAndroidMessagesProdEndpoint{
     "AndroidMessagesProdEndpoint", base::FEATURE_ENABLED_BY_DEFAULT};
 
+// Enables or disables auto screen-brightness adjustment when ambient light
+// changes.
+const base::Feature kAutoScreenBrightness{"AutoScreenBrightness",
+                                          base::FEATURE_DISABLED_BY_DEFAULT};
+
 // Enables or disables native ChromeVox support for Arc.
 const base::Feature kChromeVoxArcSupport{"ChromeVoxArcSupport",
                                          base::FEATURE_ENABLED_BY_DEFAULT};

chromeos/chromeos_features.h

@@ -17,6 +17,7 @@ namespace features {
 
 CHROMEOS_EXPORT extern const base::Feature kAndroidMessagesIntegration;
 CHROMEOS_EXPORT extern const base::Feature kAndroidMessagesProdEndpoint;
+CHROMEOS_EXPORT extern const base::Feature kAutoScreenBrightness;
 CHROMEOS_EXPORT extern const base::Feature kChromeVoxArcSupport;
 CHROMEOS_EXPORT extern const base::Feature kDriveFs;
 CHROMEOS_EXPORT extern const base::Feature kMyFilesVolume;