Android 如何实现亮度自动调节

下拉状态栏有个亮度的进度条，如果开启了亮度自动调节开关，会随着周围光线变化，这个进度条也会随着变化，接下来就是看看这个功能是如何实现的。

源码版本

基于 Android 9.0 分析。

BrightnessDialog，位于：
frameworks/base/packages/SystemUI/src/com/android/systemui/settings/BrightnessDialog.java

ToggleSliderView，位于：
frameworks/base/packages/SystemUI/src/com/android/systemui/settings/ToggleSliderView.java

DisplayPowerController，位于：
frameworks/base/services/core/java/com/android/server/display/DisplayPowerController.java

AutomaticBrightnessController，位于：
frameworks/base/services/core/java/com/android/server/display/AutomaticBrightnessController.java

BrightnessMappingStrategy，

概述

状态栏里亮度页面是 BrightnessDialog，其中进度条设置是 ToggleSliderView，亮度自动调节主要是 DisplayPowerController 和 AutomaticBrightnessController 两个类，当亮度发生变化时，如果关联到 ToggleSliderView，用的是 ContentObserver，Uri 为 Settings.System.SCREEN_AUTO_BRIGHTNESS_ADJ。

源码梳理

1、BrightnessDialog#onCreate：

@Override
protected void onCreate(Bundle savedInstanceState) {
  super.onCreate(savedInstanceState);
  //省略部分代码
  mBrightnessController = new BrightnessController(this, icon, slider);
}

2、这里进行了 BrightnessController 初始化，来看下：

public BrightnessController(Context context, ImageView icon, ToggleSlider control) {
  //省略部分代码
  mBrightnessObserver = new BrightnessObserver(mHandler);
  //省略部分代码
}

又进行了 BrightnessObserver 初始化：

/** ContentObserver to watch brightness **/
private class BrightnessObserver extends ContentObserver {
  //省略部分代码
  private final Uri BRIGHTNESS_FOR_VR_URI =
      Settings.System.getUriFor(Settings.System.SCREEN_BRIGHTNESS_FOR_VR);
  //Add By WuXiaolong for AutomaticBrightness
  private final Uri BRIGHTNESS_ADJ_URI =
      Settings.System.getUriFor(Settings.System.SCREEN_AUTO_BRIGHTNESS_ADJ);
  public BrightnessObserver(Handler handler) {
    super(handler);
  }
  @Override
  public void onChange(boolean selfChange) {
    onChange(selfChange, null);
  }
  @Override
  public void onChange(boolean selfChange, Uri uri) {
    if (selfChange) return;
    if (BRIGHTNESS_MODE_URI.equals(uri)) {
      mBackgroundHandler.post(mUpdateModeRunnable);
      mBackgroundHandler.post(mUpdateSliderRunnable);
    }
    //省略部分代码
    //Add By WuXiaolong for AutomaticBrightness
    else if (BRIGHTNESS_ADJ_URI.equals(uri) && mAutomatic) {
      mBackgroundHandler.post(mUpdateSliderRunnable);
    } else {
      mBackgroundHandler.post(mUpdateModeRunnable);
      mBackgroundHandler.post(mUpdateSliderRunnable);
    }
    for (BrightnessStateChangeCallback cb : mChangeCallbacks) {
      cb.onBrightnessLevelChanged();
    }
  }
  public void startObserving() {
    final ContentResolver cr = mContext.getContentResolver();
    cr.unregisterContentObserver(this);
    //省略部分代码
    cr.registerContentObserver(
        BRIGHTNESS_FOR_VR_URI,
        false, this, UserHandle.USER_ALL);
    //Add By WuXiaolong for AutomaticBrightness
    cr.registerContentObserver(
        BRIGHTNESS_ADJ_URI,
        false, this, UserHandle.USER_ALL);
  }
  public void stopObserving() {
    final ContentResolver cr = mContext.getContentResolver();
    cr.unregisterContentObserver(this);
  }
}

其实我目前下载的源码，这块功能是不全的，我已经加上了，哪里进行 BrightnessObserver 的 ContentObserver 注册呢？

3、回到 BrightnessDialog#onStart：

@Override
protected void onStart() {
  super.onStart();
  mBrightnessController.registerCallbacks();
  MetricsLogger.visible(this, MetricsEvent.BRIGHTNESS_DIALOG);
}

4、调用mBrightnessController.registerCallbacks();最终走到 mStartListeningRunnable：

private final Runnable mStartListeningRunnable = new Runnable() {
  @Override
  public void run() {
    //BrightnessObserver 注册
    mBrightnessObserver.startObserving();
    mUserTracker.startTracking();
    // Update the slider and mode before attaching the listener so we don't
    // receive the onChanged notifications for the initial values.
    mUpdateModeRunnable.run();
    mUpdateSliderRunnable.run();
    mHandler.sendEmptyMessage(MSG_ATTACH_LISTENER);
  }
};

当亮度有变化时，会走 BrightnessObserver#onChange，最终走到：

private final Handler mHandler = new Handler() {
  @Override
  public void handleMessage(Message msg) {
    mExternalChange = true;
    try {
      switch (msg.what) {
        //省略部分代码
        case MSG_UPDATE_SLIDER:
          updateSlider(msg.arg1, msg.arg2 != 0);
          break;
        //省略部分代码
        default:
          super.handleMessage(msg);
      }
    } finally {
      mExternalChange = false;
    }
  }
};

走 updateSlider方法，到 ：

private void animateSliderTo(int target) {
  if (!mControlValueInitialized) {
    // Don't animate the first value since it's default state isn't mea
    mControl.setValue(target);
    mControlValueInitialized = true;
  }
  //省略部分代码
}

5、跳到 ToggleSliderView#setValue：

@Override
public void setValue(int value) {
  //这里正是修改进度条
  mSlider.setProgress(value);
  if (mMirror != null) {
    mMirror.setValue(value);
  }
}

接下来就是看看亮度自动调节主要的两个类 DisplayPowerController 和 AutomaticBrightnessController。DisplayPowerController 属于 Display 模块，其控制设备屏幕亮灭、背光、与Power关系密切，这里主要看下屏幕亮度的控制这方面的逻辑。

6、首先，在 DisplayManagerService 中初始化 DisplayPowerController，如下：

private final class LocalService extends DisplayManagerInternal {
  @Override
  public void initPowerManagement(final DisplayPowerCallbacks callbacks, Handler handler,
      SensorManager sensorManager) {
    synchronized (mSyncRoot) {
      //省略部分代码
      mDisplayPowerController = new DisplayPowerController(
          mContext, callbacks, handler, sensorManager, blanker);
    }
    mHandler.sendEmptyMessage(MSG_LOAD_BRIGHTNESS_CONFIGURATION);
  }

7、接着看下 DisplayPowerController 构造方法，如下：

public DisplayPowerController(Context context,
    DisplayPowerCallbacks callbacks, Handler handler,
    SensorManager sensorManager, DisplayBlanker blanker) {
  //省略部分代码
  mUseSoftwareAutoBrightnessConfig = resources.getBoolean(
      com.android.internal.R.bool.config_automatic_brightness_available);
  //省略部分代码
  if (mUseSoftwareAutoBrightnessConfig) {
    //省略部分代码
    mBrightnessMapper = BrightnessMappingStrategy.create(resources);
    if (mBrightnessMapper != null) {
      mAutomaticBrightnessController = new AutomaticBrightnessController(this,
          handler.getLooper(), sensorManager, mBrightnessMapper,
          lightSensorWarmUpTimeConfig, mScreenBrightnessRangeMinimum,
          mScreenBrightnessRangeMaximum, dozeScaleFactor, lightSensorRate,
          initialLightSensorRate, brighteningLightDebounce, darkeningLightDebounce,
          autoBrightnessResetAmbientLuxAfterWarmUp, hysteresisLevels);
    } else {
      mUseSoftwareAutoBrightnessConfig = false;
    }
  }
  //省略部分代码
  mAutoBrightnessAdjustment = getAutoBrightnessAdjustmentSetting();
  mTemporaryAutoBrightnessAdjustment = Float.NaN;
  //省略部分代码
}

由于亮屏之后屏幕自动亮度才会生效，所以在亮屏的时候，流程会走到 DisplayPowerController 中的核心函数 updatePowerState()：

private void updatePowerState() {
  // Update the power state request.
  //省略部分代码

  final boolean autoBrightnessAdjustmentChanged = updateAutoBrightnessAdjustment();
  if (autoBrightnessAdjustmentChanged) {
    mTemporaryAutoBrightnessAdjustment = Float.NaN;
  }
  // Use the autobrightness adjustment override if set.
  final float autoBrightnessAdjustment;
  if (!Float.isNaN(mTemporaryAutoBrightnessAdjustment)) {
    autoBrightnessAdjustment = mTemporaryAutoBrightnessAdjustment;
    mAppliedTemporaryAutoBrightnessAdjustment = true;
  } else {
    autoBrightnessAdjustment = mAutoBrightnessAdjustment;
    mAppliedTemporaryAutoBrightnessAdjustment = false;
  }

  boolean hadUserBrightnessPoint = false;
  // Configure auto-brightness.
  if (mAutomaticBrightnessController != null) {
    hadUserBrightnessPoint = mAutomaticBrightnessController.hasUserDataPoints();
    mAutomaticBrightnessController.configure(autoBrightnessEnabled,
        mBrightnessConfiguration,
        mLastUserSetScreenBrightness / (float) PowerManager.BRIGHTNESS_ON,
        userSetBrightnessChanged, autoBrightnessAdjustment,
        autoBrightnessAdjustmentChanged, mPowerRequest.policy);
  }

  // Apply auto-brightness.
  boolean slowChange = false;
  if (brightness < 0) {
    float newAutoBrightnessAdjustment = autoBrightnessAdjustment;
    if (autoBrightnessEnabled) {
      brightness = mAutomaticBrightnessController.getAutomaticScreenBrightness();
      newAutoBrightnessAdjustment =
          mAutomaticBrightnessController.getAutomaticScreenBrightnessAdjustment();
    }
    if (brightness >= 0) {
      // Use current auto-brightness value and slowly adjust to changes.
      brightness = clampScreenBrightness(brightness);
      if (mAppliedAutoBrightness && !autoBrightnessAdjustmentChanged) {
        slowChange = true; // slowly adapt to auto-brightness
      }
      // Tell the rest of the system about the new brightness. Note that we do this
      // before applying the low power or dim transformations so that the slider
      // accurately represents the full possible range, even if they range changes what
      // it means in absolute terms.
      putScreenBrightnessSetting(brightness);
      mAppliedAutoBrightness = true;
    } else {
      mAppliedAutoBrightness = false;
    }
    if (autoBrightnessAdjustment != newAutoBrightnessAdjustment) {
      // If the autobrightness controller has decided to change the adjustment value
      // used, make sure that's reflected in settings.
      putAutoBrightnessAdjustmentSetting(newAutoBrightnessAdjustment);
    }
  } else {
    mAppliedAutoBrightness = false;
  }
  //省略部分代码
}

接下来分别看看 autoBrightnessAdjustment 和 newAutoBrightnessAdjustment 怎么来的？

autoBrightnessAdjustment 是来自 mTemporaryAutoBrightnessAdjustment 或 mAutoBrightnessAdjustment 赋值，mAutoBrightnessAdjustment 在第 7 步mAutoBrightnessAdjustment = getAutoBrightnessAdjustmentSetting();有初始化，看下 getAutoBrightnessAdjustmentSetting()：

private float getAutoBrightnessAdjustmentSetting() {
  final float adj = Settings.System.getFloatForUser(mContext.getContentResolver(),
      Settings.System.SCREEN_AUTO_BRIGHTNESS_ADJ, 0.0f, UserHandle.USER_CURRENT);
  return Float.isNaN(adj) ? 0.0f : clampAutoBrightnessAdjustment(adj);
}

继续看下 clampAutoBrightnessAdjustment：

private static float clampAutoBrightnessAdjustment(float value) {
  return MathUtils.constrain(value, -1.0f, 1.0f);
}

这里注意下 MathUtils.constrain() 表示百分比缩放函数，比如 MathUtils.constrain(0.5, 0, 255) 表示 （255-0）*0.5。

这样了解了 autoBrightnessAdjustment，接下来看 newAutoBrightnessAdjustment。

8、回到 DisplayPowerController#updatePowerState()，

看到 newAutoBrightnessAdjustment 调用了 AutomaticBrightnessController.getAutomaticScreenBrightnessAdjustment()，最终是到了 BrightnessMapper#getAutoBrightnessAdjustment() 其中 mAutoBrightnessAdjustment 变量，赋值是在 BrightnessMapper#setAutoBrightnessAdjustment：

@Override
public boolean setAutoBrightnessAdjustment(float adjustment) {
  adjustment = MathUtils.constrain(adjustment, -1, 1);
  if (adjustment == mAutoBrightnessAdjustment) {
    return false;
  }
  if (DEBUG) {
    Slog.d(TAG, "setAutoBrightnessAdjustment: " + mAutoBrightnessAdjustment + " => " +
        adjustment);
    PLOG.start("auto-brightness adjustment");
  }
  mAutoBrightnessAdjustment = adjustment;
  computeSpline();
  return true;
}

9、BrightnessMapper#setAutoBrightnessAdjustment

这个方法调用又回到了 AutomaticBrightnessController#setAutoBrightnessAdjustment：

private boolean setAutoBrightnessAdjustment(float adjustment) {
  return mBrightnessMapper.setAutoBrightnessAdjustment(adjustment);
}

AutomaticBrightnessController#setAutoBrightnessAdjustment调用是来到 AutomaticBrightnessController#configure()方法：

public void configure(boolean enable, @Nullable BrightnessConfiguration configuration,
    float brightness, boolean userChangedBrightness, float adjustment,
    boolean userChangedAutoBrightnessAdjustment, int displayPolicy) {
  // While dozing, the application processor may be suspended which will prevent us from
  // receiving new information from the light sensor. On some devices, we may be able to
  // switch to a wake-up light sensor instead but for now we will simply disable the sensor
  // and hold onto the last computed screen auto brightness. We save the dozing flag for
  // debugging purposes.
  boolean dozing = (displayPolicy == DisplayPowerRequest.POLICY_DOZE);
  boolean changed = setBrightnessConfiguration(configuration);
  changed |= setDisplayPolicy(displayPolicy);
  if (userChangedAutoBrightnessAdjustment) {
    changed |= setAutoBrightnessAdjustment(adjustment);
  }
  if (userChangedBrightness && enable) {
    // Update the brightness curve with the new user control point. It's critical this
    // happens after we update the autobrightness adjustment since it may reset it.
    changed |= setScreenBrightnessByUser(brightness);
  }
  final boolean userInitiatedChange =
      userChangedBrightness || userChangedAutoBrightnessAdjustment;
  if (userInitiatedChange && enable && !dozing) {
    prepareBrightnessAdjustmentSample();
  }
  changed |= setLightSensorEnabled(enable && !dozing);
  if (changed) {
    updateAutoBrightness(false /*sendUpdate*/);
  }
}

AutomaticBrightnessController#configure()调用来到了 DisplayPowerController #updatePowerState()。

这样也知道了 newAutoBrightnessAdjustment，继续 putAutoBrightnessAdjustmentSetting：

private void putAutoBrightnessAdjustmentSetting(float adjustment) {
  mAutoBrightnessAdjustment = adjustment;
  Settings.System.putFloatForUser(mContext.getContentResolver(),
      Settings.System.SCREEN_AUTO_BRIGHTNESS_ADJ, adjustment, UserHandle.USER_CURRENT);
}

就调到第 4 步 BrightnessObserver#onChange，进度条随之变化，Over！

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