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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 /**
     22  * A helper class for handling access to illuminance hysteresis level values.
     23  */
     24 final class HysteresisLevels {
     25     private static final String TAG = "HysteresisLevels";
     26 
     27     // Default hysteresis constraints for brightening or darkening.
     28     // The recent lux must have changed by at least this fraction relative to the
     29     // current ambient lux before a change will be considered.
     30     private static final float DEFAULT_BRIGHTENING_HYSTERESIS = 0.10f;
     31     private static final float DEFAULT_DARKENING_HYSTERESIS = 0.20f;
     32 
     33     private static final boolean DEBUG = false;
     34 
     35     private final float[] mBrightLevels;
     36     private final float[] mDarkLevels;
     37     private final float[] mLuxLevels;
     38 
     39   /**
     40    * Creates a {@code HysteresisLevels} object with the given equal-length
     41    * integer arrays.
     42    * @param brightLevels an array of brightening hysteresis constraint constants
     43    * @param darkLevels an array of darkening hysteresis constraint constants
     44    * @param luxLevels a monotonically increasing array of illuminance
     45    *                  thresholds in units of lux
     46    */
     47     public HysteresisLevels(int[] brightLevels, int[] darkLevels, int[] luxLevels) {
     48         if (brightLevels.length != darkLevels.length || darkLevels.length != luxLevels.length + 1) {
     49             throw new IllegalArgumentException("Mismatch between hysteresis array lengths.");
     50         }
     51         mBrightLevels = setArrayFormat(brightLevels, 1000.0f);
     52         mDarkLevels = setArrayFormat(darkLevels, 1000.0f);
     53         mLuxLevels = setArrayFormat(luxLevels, 1.0f);
     54     }
     55 
     56     /**
     57      * Return the brightening hysteresis threshold for the given lux level.
     58      */
     59     public float getBrighteningThreshold(float lux) {
     60         float brightConstant = getReferenceLevel(lux, mBrightLevels);
     61         float brightThreshold = lux * (1.0f + brightConstant);
     62         if (DEBUG) {
     63             Slog.d(TAG, "bright hysteresis constant=: " + brightConstant + ", threshold="
     64                 + brightThreshold + ", lux=" + lux);
     65         }
     66         return brightThreshold;
     67     }
     68 
     69     /**
     70      * Return the darkening hysteresis threshold for the given lux level.
     71      */
     72     public float getDarkeningThreshold(float lux) {
     73         float darkConstant = getReferenceLevel(lux, mDarkLevels);
     74         float darkThreshold = lux * (1.0f - darkConstant);
     75         if (DEBUG) {
     76             Slog.d(TAG, "dark hysteresis constant=: " + darkConstant + ", threshold="
     77                 + darkThreshold + ", lux=" + lux);
     78         }
     79         return darkThreshold;
     80     }
     81 
     82     /**
     83      * Return the hysteresis constant for the closest lux threshold value to the
     84      * current illuminance from the given array.
     85      */
     86     private float getReferenceLevel(float lux, float[] referenceLevels) {
     87         int index = 0;
     88         while (mLuxLevels.length > index && lux >= mLuxLevels[index]) {
     89             ++index;
     90         }
     91         return referenceLevels[index];
     92     }
     93 
     94     /**
     95      * Return a float array where each i-th element equals {@code configArray[i]/divideFactor}.
     96      */
     97     private float[] setArrayFormat(int[] configArray, float divideFactor) {
     98         float[] levelArray = new float[configArray.length];
     99         for (int index = 0; levelArray.length > index; ++index) {
    100             levelArray[index] = (float)configArray[index] / divideFactor;
    101         }
    102         return levelArray;
    103     }
    104 }
    105