亮度设置
应用设计
1.1 设置进度条范围
背光设置是在：设置->声音和显示->亮度，通过进度条来设置的。
文件：packages/apps/Settings/src/com/Android/settings/BrightnessPreference.java
private static final int MINIMUM_BACKLIGHT = android.os.Power.BRIGHTNESS_DIM + 10;
private static final int MAXIMUM_BACKLIGHT = android.os.Power.BRIGHTNESS_ON;
mSeekBar.setMax(MAXIMUM_BACKLIGHT - MINIMUM_BACKLIGHT);
设置进度条的范围，BRIGHTNESS_DIM = 20 BRIGHTNESS_ON=255，它们的定义在：
frameworks/base/core/java/android/os/Power.java
1.2 设置亮度
文件：packages/apps/Settings/src/com/android/settings/BrightnessPreference.java
public void onCheckedChanged(CompoundButton buttonView, boolean isChecked) {
setMode(isChecked ? Settings.System.SCREEN_BRIGHTNESS_MODE_AUTOMATIC
: Settings.System.SCREEN_BRIGHTNESS_MODE_MANUAL);
if (!isChecked) {
setBrightness(mSeekBar.getProgress() + MINIMUM_BACKLIGHT);
}
}
private void setBrightness(int brightness) {
try {
IPowerManager power = IPowerManager.Stub.asInterface(
ServiceManager.getService("power"));
if (power != null) {
power.setBacklightBrightness(brightness);
}
} catch (RemoteException doe) {
}
}
由以上代码可知，brightness的范围是：20~255;代码通过服务管理器(ServiceManager)获得power服务，然后通过power服务设置亮度。
power.setBacklightBrightness的定义在：
rameworks/base/core/java/android/os/IPowerManager.aidl.java
frameworks/base/core/java/android/os/PowerManager.java
2， Power服务
文件：frameworks/base/core/java/android/os/Power.java
/**
* Brightness value for dim backlight
*/
public static final int BRIGHTNESS_DIM = 20;
/**
* Brightness value for fully on
*/
public static final int BRIGHTNESS_ON = 255;
文件：frameworks/base/core/java/android/os/PowerManager.java
/**
* sets the brightness of the backlights (screen, keyboard, button).
*
* @param brightness value from 0 to 255
*
* {@hide}
*/
public void setBacklightBrightness(int brightness)
{
try {
mService.setBacklightBrightness(brightness);
} catch (RemoteException e) {
}
}
电源管理器(powermager)将brightness转给电源服务，该服务位置如下：
文件：frameworks/base/services/java/com/android/server/PowerManagerService.java
public void setBacklightBrightness(int brightness) {
mContext.enforceCallingOrSelfPermission(android.Manifest.permission.DEVICE_POWER, null);
// Don't let applications turn the screen all the way off
brightness = Math.max(brightness, Power.BRIGHTNESS_DIM);
mHardware.setLightBrightness_UNCHECKED(HardwareService.LIGHT_ID_BACKLIGHT, brightness,
HardwareService.BRIGHTNESS_MODE_USER);
mHardware.setLightBrightness_UNCHECKED(HardwareService.LIGHT_ID_KEYBOARD,
(mKeyboardVisible ? brightness : 0), HardwareService.BRIGHTNESS_MODE_USER);
mHardware.setLightBrightness_UNCHECKED(HardwareService.LIGHT_ID_BUTTONS, brightness,
HardwareService.BRIGHTNESS_MODE_USER);
long identity = Binder.clearCallingIdentity();
try {
mBatteryStats.noteScreenBrightness(brightness);
} catch (RemoteException e) {
Log.w(TAG, "RemoteException calling noteScreenBrightness on BatteryStatsService", e);
} finally {
Binder.restoreCallingIdentity(identity);
}
// update our animation state
if (ANIMATE_SCREEN_LIGHTS) {
mScreenBrightness.curValue = brightness;
mScreenBrightness.animating = false;
mScreenBrightness.targetValue = -1;
}
if (ANIMATE_KEYBOARD_LIGHTS) {
mKeyboardBrightness.curValue = brightness;
mKeyboardBrightness.animating = false;
mKeyboardBrightness.targetValue = -1;
}
if (ANIMATE_BUTTON_LIGHTS) {
mButtonBrightness.curValue = brightness;
mButtonBrightness.animating = false;
mButtonBrightness.targetValue = -1;
}
}
由以上代码可知，同时设置了背光、键盘、按钮的亮度。mHardware 是硬件服务，通过该服务调用底层与设备打交道的C\C++代码，setLightBrightness_UNCHECKED原型如下：
文件：frameworks/base/services\java\com\android\server\HardwareService.java
void setLightBrightness_UNCHECKED(int light, int brightness, int brightnessMode) {
int b = brightness & 0x000000ff;
b = 0xff000000 | (b << 16) | (b << 8) | b;
setLight_native(mNativePointer, light, b, LIGHT_FLASH_NONE, 0, 0, brightnessMode);
}