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      1 /*
      2  * Copyright (C) 2016 The Android Open Source Project
      3  *
      4  * Licensed under the Apache License, Version 2.0 (the "License");
      5  * you may not use this file except in compliance with the License.
      6  * You may obtain a copy of the License at
      7  *
      8  *      http://www.apache.org/licenses/LICENSE-2.0
      9  *
     10  * Unless required by applicable law or agreed to in writing, software
     11  * distributed under the License is distributed on an "AS IS" BASIS,
     12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
     13  * See the License for the specific language governing permissions and
     14  * limitations under the License.
     15  */
     16 
     17 package com.android.server.display;
     18 
     19 import android.util.Slog;
     20 
     21 import java.io.PrintWriter;
     22 import java.util.Arrays;
     23 
     24 /**
     25  * A helper class for handling access to illuminance hysteresis level values.
     26  */
     27 final class HysteresisLevels {
     28     private static final String TAG = "HysteresisLevels";
     29 
     30     // Default hysteresis constraints for brightening or darkening.
     31     // The recent lux must have changed by at least this fraction relative to the
     32     // current ambient lux before a change will be considered.
     33     private static final float DEFAULT_BRIGHTENING_HYSTERESIS = 0.10f;
     34     private static final float DEFAULT_DARKENING_HYSTERESIS = 0.20f;
     35 
     36     private static final boolean DEBUG = false;
     37 
     38     private final float[] mBrightLevels;
     39     private final float[] mDarkLevels;
     40     private final float[] mLuxLevels;
     41 
     42   /**
     43    * Creates a {@code HysteresisLevels} object with the given equal-length
     44    * integer arrays.
     45    * @param brightLevels an array of brightening hysteresis constraint constants
     46    * @param darkLevels an array of darkening hysteresis constraint constants
     47    * @param luxLevels a monotonically increasing array of illuminance
     48    *                  thresholds in units of lux
     49    */
     50     public HysteresisLevels(int[] brightLevels, int[] darkLevels, int[] luxLevels) {
     51         if (brightLevels.length != darkLevels.length || darkLevels.length != luxLevels.length + 1) {
     52             throw new IllegalArgumentException("Mismatch between hysteresis array lengths.");
     53         }
     54         mBrightLevels = setArrayFormat(brightLevels, 1000.0f);
     55         mDarkLevels = setArrayFormat(darkLevels, 1000.0f);
     56         mLuxLevels = setArrayFormat(luxLevels, 1.0f);
     57     }
     58 
     59     /**
     60      * Return the brightening hysteresis threshold for the given lux level.
     61      */
     62     public float getBrighteningThreshold(float lux) {
     63         float brightConstant = getReferenceLevel(lux, mBrightLevels);
     64         float brightThreshold = lux * (1.0f + brightConstant);
     65         if (DEBUG) {
     66             Slog.d(TAG, "bright hysteresis constant=: " + brightConstant + ", threshold="
     67                 + brightThreshold + ", lux=" + lux);
     68         }
     69         return brightThreshold;
     70     }
     71 
     72     /**
     73      * Return the darkening hysteresis threshold for the given lux level.
     74      */
     75     public float getDarkeningThreshold(float lux) {
     76         float darkConstant = getReferenceLevel(lux, mDarkLevels);
     77         float darkThreshold = lux * (1.0f - darkConstant);
     78         if (DEBUG) {
     79             Slog.d(TAG, "dark hysteresis constant=: " + darkConstant + ", threshold="
     80                 + darkThreshold + ", lux=" + lux);
     81         }
     82         return darkThreshold;
     83     }
     84 
     85     /**
     86      * Return the hysteresis constant for the closest lux threshold value to the
     87      * current illuminance from the given array.
     88      */
     89     private float getReferenceLevel(float lux, float[] referenceLevels) {
     90         int index = 0;
     91         while (mLuxLevels.length > index && lux >= mLuxLevels[index]) {
     92             ++index;
     93         }
     94         return referenceLevels[index];
     95     }
     96 
     97     /**
     98      * Return a float array where each i-th element equals {@code configArray[i]/divideFactor}.
     99      */
    100     private float[] setArrayFormat(int[] configArray, float divideFactor) {
    101         float[] levelArray = new float[configArray.length];
    102         for (int index = 0; levelArray.length > index; ++index) {
    103             levelArray[index] = (float)configArray[index] / divideFactor;
    104         }
    105         return levelArray;
    106     }
    107 
    108     public void dump(PrintWriter pw) {
    109         pw.println("HysteresisLevels");
    110         pw.println("  mBrightLevels=" + Arrays.toString(mBrightLevels));
    111         pw.println("  mDarkLevels=" + Arrays.toString(mDarkLevels));
    112         pw.println("  mLuxLevels=" + Arrays.toString(mLuxLevels));
    113     }
    114 }
    115