1、安卓每个版本的更新， 其核心代码也会随之更新，本次为Android 12 版本默认屏幕亮度的修改。
其中涉及的核心代码主要有：
java
packages\apps\Settings\src\com\android\settings\display\BrightnessLevelPreferenceController.java
frameworks\base\services\core\java\com\android\server\power\PowerManagerService.java
frameworks/base/res/res/values/config.xml2、设置默认亮度的主要方法代码
在BrightnessLevelPreferenceController中处理：
java
public class BrightnessLevelPreferenceController extends AbstractPreferenceController implements
PreferenceControllerMixin, LifecycleObserver, OnStart, OnStop {
private ContentObserver mBrightnessObserver =
new ContentObserver(new Handler(Looper.getMainLooper())) {
@Override
public void onChange(boolean selfChange) {
updatedSummary(mPreference);
}
};
public BrightnessLevelPreferenceController(Context context, Lifecycle lifecycle) {
super(context);
if (lifecycle != null) {
lifecycle.addObserver(this);
}
PowerManager powerManager = (PowerManager) context.getSystemService(Context.POWER_SERVICE);
mMinBrightness = powerManager.getBrightnessConstraint(
PowerManager.BRIGHTNESS_CONSTRAINT_TYPE_MINIMUM);
mMaxBrightness = powerManager.getBrightnessConstraint(
PowerManager.BRIGHTNESS_CONSTRAINT_TYPE_MAXIMUM);
mMinVrBrightness = powerManager.getBrightnessConstraint(
PowerManager.BRIGHTNESS_CONSTRAINT_TYPE_MINIMUM_VR);
mMaxVrBrightness = powerManager.getBrightnessConstraint(
PowerManager.BRIGHTNESS_CONSTRAINT_TYPE_MAXIMUM_VR);
mContentResolver = mContext.getContentResolver();
mDefaultBacklight = powerManager.getBrightnessConstraint(
PowerManager.BRIGHTNESS_CONSTRAINT_TYPE_DEFAULT);
}在PowerManager得到相应的值：
java
private void updatedSummary(Preference preference) {
if (preference != null) {
preference.setSummary(NumberFormat.getPercentInstance().format(getCurrentBrightness()));
}
}
private double getCurrentBrightness() {
final int value;
if (isInVrMode()) {
value = convertLinearToGammaFloat(System.getFloat(mContentResolver,
System.SCREEN_BRIGHTNESS_FOR_VR_FLOAT, mMaxBrightness),
mMinVrBrightness, mMaxVrBrightness);
} else {
value = convertLinearToGammaFloat(Settings.System.getFloat(mContentResolver,
System.SCREEN_BRIGHTNESS_FLOAT, mDefaultBacklight),
mMinBrightness, mMaxBrightness);
}
return getPercentage(value, GAMMA_SPACE_MIN, GAMMA_SPACE_MAX);
}
private double getPercentage(double value, int min, int max) {
if (value > max) {
return 1.0;
}
if (value < min) {
return 0.0;
}
return (value - min) / (max - min);
}...
java
public final class PowerManagerService extends SystemService
implements Watchdog.Monitor {
@VisibleForTesting
PowerManagerService(Context context, Injector injector) {
super(context);
mContext = context;
......
// Save brightness values:
// Get float values from config.
// Store float if valid
// Otherwise, get int values and convert to float and then store.
final float min = mContext.getResources().getFloat(com.android.internal.R.dimen
.config_screenBrightnessSettingMinimumFloat);
final float max = mContext.getResources().getFloat(com.android.internal.R.dimen
.config_screenBrightnessSettingMaximumFloat);
final float def = mContext.getResources().getFloat(com.android.internal.R.dimen
.config_screenBrightnessSettingDefaultFloat);
final float doze = mContext.getResources().getFloat(com.android.internal.R.dimen
.config_screenBrightnessDozeFloat);
final float dim = mContext.getResources().getFloat(com.android.internal.R.dimen
.config_screenBrightnessDimFloat);
if (min == INVALID_BRIGHTNESS_IN_CONFIG || max == INVALID_BRIGHTNESS_IN_CONFIG
|| def == INVALID_BRIGHTNESS_IN_CONFIG) {
mScreenBrightnessMinimum = BrightnessSynchronizer.brightnessIntToFloat(
mContext.getResources().getInteger(com.android.internal.R.integer
.config_screenBrightnessSettingMinimum),
PowerManager.BRIGHTNESS_OFF + 1, PowerManager.BRIGHTNESS_ON,
PowerManager.BRIGHTNESS_MIN, PowerManager.BRIGHTNESS_MAX);
mScreenBrightnessMaximum = BrightnessSynchronizer.brightnessIntToFloat(
mContext.getResources().getInteger(com.android.internal.R.integer
.config_screenBrightnessSettingMaximum),
PowerManager.BRIGHTNESS_OFF + 1, PowerManager.BRIGHTNESS_ON,
PowerManager.BRIGHTNESS_MIN, PowerManager.BRIGHTNESS_MAX);
mScreenBrightnessDefault = BrightnessSynchronizer.brightnessIntToFloat(
mContext.getResources().getInteger(com.android.internal.R.integer
.config_screenBrightnessSettingDefault),
PowerManager.BRIGHTNESS_OFF + 1, PowerManager.BRIGHTNESS_ON,
PowerManager.BRIGHTNESS_MIN, PowerManager.BRIGHTNESS_MAX);
} else {
mScreenBrightnessMinimum = min;
mScreenBrightnessMaximum = max;
mScreenBrightnessDefault = def;
}
..
}其中它是通过config中实现的：
java
public float getBrightnessConstraint(int constraint) {
switch (constraint) {
case PowerManager.BRIGHTNESS_CONSTRAINT_TYPE_MINIMUM:
return mScreenBrightnessMinimum;
case PowerManager.BRIGHTNESS_CONSTRAINT_TYPE_MAXIMUM:
return mScreenBrightnessMaximum;
case PowerManager.BRIGHTNESS_CONSTRAINT_TYPE_DEFAULT:
return mScreenBrightnessDefault;
case PowerManager.BRIGHTNESS_CONSTRAINT_TYPE_DIM:
return mScreenBrightnessDim;
case PowerManager.BRIGHTNESS_CONSTRAINT_TYPE_DOZE:
return mScreenBrightnessDoze;
case PowerManager.BRIGHTNESS_CONSTRAINT_TYPE_MINIMUM_VR:
return mScreenBrightnessMinimumVr;
case PowerManager.BRIGHTNESS_CONSTRAINT_TYPE_MAXIMUM_VR:
return mScreenBrightnessMaximumVr;
case PowerManager.BRIGHTNESS_CONSTRAINT_TYPE_DEFAULT_VR:
return mScreenBrightnessDefaultVr;
default:
return PowerManager.BRIGHTNESS_INVALID_FLOAT;
}
}3、修改代码的位置：
--- a/frameworks/base/res/res/values/config.xml
+++ b//frameworks/base/res/res/values/config.xml
@@ -28,5 +28,5 @@
<item name="config_screenBrightnessSettingMaximumFloat" format="float" type="dimen">1.0</item>
<!-- Default screen brightness setting set.
Set this to 0.4 for Default brightness Float.-->
- <item name="config_screenBrightnessSettingDefaultFloat" format="float" type="dimen">0.3</item>
+ <item name="config_screenBrightnessSettingDefaultFloat" format="float" type="dimen">0.4</item>
</resources>