android 设置系统屏幕亮度

转自：http://blog.csdn.net/skdev/article/details/5335554

网上都到的都是下面这种，并不是真正设置系统的亮度：

public void onSharedPreferenceChanged(SharedPreferences sp, String key) {
// TODO Auto-generated method stub
if(TextUtils.equals(key, "brightness")){
int brightness=sp.getInt("brightness", 125);
LayoutParams lp=   getWindow().getAttributes();
lp.screenBrightness=brightness/255.0f;
getWindow().setAttributes(lp);
}

下面这位分析的非常详细:

3 亮度设置

3.1 应用设计

3.1.1 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

3.1.2 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

3.2 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);

}

参数说明：int light 表示类型，选项如下：

static final int LIGHT_ID_BACKLIGHT = 0;

static final int LIGHT_ID_KEYBOARD = 1;

static final int LIGHT_ID_BUTTONS = 2;

static final int LIGHT_ID_BATTERY = 3;

static final int LIGHT_ID_NOTIFICATIONS = 4;

static final int LIGHT_ID_ATTENTION = 5;

int brightness 表示亮度值

int brightnessMode 表示亮度的控制模式，选项如下：

/**

* Light brightness is managed by a user setting.

static final int BRIGHTNESS_MODE_USER = 0;

/**

* Light brightness is managed by a light sensor.

static final int BRIGHTNESS_MODE_SENSOR = 1;

由代码：

int b = brightness & 0x000000ff;

b = 0xff000000 | (b << 16) | (b << 8) | b;

可知，亮度值在此进行了修改，即亮度值的格式变成：FFRRGGBB，FF是没有的，RR、GG、BB分别是256色的红绿蓝，并且红绿蓝的值都是一样的亮度值。

3.3 硬件调用

3.3.1获取硬件

文件：frameworks/base/services/jni/com_android_server_HardwareService.cpp

enum {

LIGHT_INDEX_BACKLIGHT = 0,

LIGHT_INDEX_KEYBOARD = 1,

LIGHT_INDEX_BUTTONS = 2,

LIGHT_INDEX_BATTERY = 3,

LIGHT_INDEX_NOTIFICATIONS = 4,

LIGHT_INDEX_ATTENTION = 5,

LIGHT_COUNT

};

#define LIGHTS_HARDWARE_MODULE_ID "lights"

static jint init_native(JNIEnv *env, jobject clazz)

{

int err;

hw_module_t* module;

Devices* devices;

devices = (Devices*)malloc(sizeof(Devices));

err = hw_get_module(LIGHTS_HARDWARE_MODULE_ID, (hw_module_t const**)&module);

if (err == 0) {

devices->lights[LIGHT_INDEX_BACKLIGHT]

= get_device(module, LIGHT_ID_BACKLIGHT);

devices->lights[LIGHT_INDEX_KEYBOARD]

= get_device(module, LIGHT_ID_KEYBOARD);

devices->lights[LIGHT_INDEX_BUTTONS]

= get_device(module, LIGHT_ID_BUTTONS);

devices->lights[LIGHT_INDEX_BATTERY]

= get_device(module, LIGHT_ID_BATTERY);

devices->lights[LIGHT_INDEX_NOTIFICATIONS]

= get_device(module, LIGHT_ID_NOTIFICATIONS);

devices->lights[LIGHT_INDEX_ATTENTION]

= get_device(module, LIGHT_ID_ATTENTION);

} else {

memset(devices, 0, sizeof(Devices));

}

return (jint)devices;

}

用hw_get_module获取ID为LIGHTS_HARDWARE_MODULE_ID的硬件模块，该模块含有6个不同类型的亮度控制。

hw_get_module 的实现原理，如下：

文件：hardware/libhardware/Hardware.c

#define HAL_LIBRARY_PATH "/system/lib/hw"

static const char *variant_keys[] = {

"ro.hardware", /* This goes first so that it can pick up a different

file on the emulator. */

"ro.product.board",

"ro.board.platform",

"ro.arch"

};

static const int HAL_VARIANT_KEYS_COUNT =

(sizeof(variant_keys)/sizeof(variant_keys[0]));

int hw_get_module(const char *id, const struct hw_module_t **module)

{

int status;

int i;

const struct hw_module_t *hmi = NULL;

char prop[PATH_MAX];

char path[PATH_MAX];

* Here we rely on the fact that calling dlopen multiple times on

* the same .so will simply increment a refcount (and not load

* a new copy of the library).

* We also assume that dlopen() is thread-safe.

/* Loop through the configuration variants looking for a module */

for (i=0 ; i<HAL_VARIANT_KEYS_COUNT+1 ; i++) {

if (i < HAL_VARIANT_KEYS_COUNT) {

if (property_get(variant_keys[i], prop, NULL) == 0) {

continue;

}

snprintf(path, sizeof(path), "%s/%s.%s.so",

HAL_LIBRARY_PATH, id, prop);

} else {

snprintf(path, sizeof(path), "%s/%s.default.so",

HAL_LIBRARY_PATH, id);

}

if (access(path, R_OK)) {

continue;

}

/* we found a library matching this id/variant */

break;

}

status = -ENOENT;

if (i < HAL_VARIANT_KEYS_COUNT+1) {

/* load the module, if this fails, we're doomed, and we should not try

* to load a different variant. */

status = load(id, path, module);

}

return status;

}

property_get(variant_keys[i], prop, NULL) 会按如下顺序去获取如下变量所对应的值，然后返回给prop：

"ro.hardware", /* This goes first so that it can pick up a different

file on the emulator. */

"ro.product.board",

"ro.board.platform",

"ro.arch"

它们对应的变量为：

"ro.product.board=$TARGET_BOOTLOADER_BOARD_NAME"

"ro.board.platform=$TARGET_BOARD_PLATFORM"

如vendor/htc/dream-open/BoardConfig.mk里定义的TARGET_BOARD_PLATFORM := msm7k，则prop返回” msm7k ”，所以path = /system/lib/hw/lights. msm7k.so，也就是说要获取的硬件模块为lights. msm7k.so。

3.3.2调用硬件

setLight_native对应的jni C/C++代码是：

文件：frameworks/base/services/jni/com_android_server_HardwareService.cpp

static void setLight_native(JNIEnv *env, jobject clazz, int ptr,

int light, int colorARGB, int flashMode, int onMS, int offMS, int brightnessMode)

{

Devices* devices = (Devices*)ptr;

light_state_t state;

if (light < 0 || light >= LIGHT_COUNT || devices->lights[light] == NULL) {

return ;

}

memset(&state, 0, sizeof(light_state_t));

state.color = colorARGB;

state.flashMode = flashMode;

state.flashOnMS = onMS;

state.flashOffMS = offMS;

state.brightnessMode = brightnessMode;

devices->lights[light]->set_light(devices->lights[light], &state);

}

通过light标识找到对应的light设备，然后再设置亮度。

3.3.3 硬件原型

msm7k的lights对应的硬件原型是在：hardware/msm7k/liblights

文件：hardware/msm7k/liblights/Android.mk

LOCAL_MODULE_PATH := $(TARGET_OUT_SHARED_LIBRARIES)/hw

LOCAL_MODULE := lights.$(TARGET_BOARD_PLATFORM)

也就是生成模块：/system/lib/hw/lights. msm7k.so

文件：hardware/msm7k/liblights/lights.c

/** Open a new instance of a lights device using name */

static int open_lights(const struct hw_module_t* module, char const* name,

struct hw_device_t** device)

{

int (*set_light)(struct light_device_t* dev,

struct light_state_t const* state);

if (0 == strcmp(LIGHT_ID_BACKLIGHT, name)) {

set_light = set_light_backlight;

}

else if (0 == strcmp(LIGHT_ID_KEYBOARD, name)) {

set_light = set_light_keyboard;

}

else if (0 == strcmp(LIGHT_ID_BUTTONS, name)) {

set_light = set_light_buttons;

}

else if (0 == strcmp(LIGHT_ID_BATTERY, name)) {

set_light = set_light_battery;

}

else if (0 == strcmp(LIGHT_ID_NOTIFICATIONS, name)) {

set_light = set_light_notifications;

}

else if (0 == strcmp(LIGHT_ID_ATTENTION, name)) {

set_light = set_light_attention;

}

else {

return -EINVAL;

}

pthread_once(&g_init, init_globals);

struct light_device_t *dev = malloc(sizeof(struct light_device_t));

memset(dev, 0, sizeof(*dev));

dev->common.tag = HARDWARE_DEVICE_TAG;

dev->common.version = 0;

dev->common.module = (struct hw_module_t*)module;

dev->common.close = (int (*)(struct hw_device_t*))close_lights;

dev->set_light = set_light;

*device = (struct hw_device_t*)dev;

return 0;

}

static struct hw_module_methods_t lights_module_methods = {

.open = open_lights,

};

以上代码对应的是：

devices->lights[LIGHT_INDEX_BACKLIGHT]

= get_device(module, LIGHT_ID_BACKLIGHT);

devices->lights[LIGHT_INDEX_KEYBOARD]

= get_device(module, LIGHT_ID_KEYBOARD);

devices->lights[LIGHT_INDEX_BUTTONS]

= get_device(module, LIGHT_ID_BUTTONS);

devices->lights[LIGHT_INDEX_BATTERY]

= get_device(module, LIGHT_ID_BATTERY);

devices->lights[LIGHT_INDEX_NOTIFICATIONS]

= get_device(module, LIGHT_ID_NOTIFICATIONS);

devices->lights[LIGHT_INDEX_ATTENTION]

= get_device(module, LIGHT_ID_ATTENTION);

也就是说，对不同的亮度设置给予了不同的设置函数。

举例，背光设置，背光对应的代码如下：

char const*const LCD_FILE

= "/sys/class/leds/lcd-backlight/brightness";

static int

rgb_to_brightness(struct light_state_t const* state)

{

int color = state->color & 0x00ffffff;

return ((77*((color>>16)&0x00ff))

+ (150*((color>>8)&0x00ff)) + (29*(color&0x00ff))) >> 8;

}

static int

set_light_backlight(struct light_device_t* dev,

struct light_state_t const* state)

{

int err = 0;

int brightness = rgb_to_brightness(state);

pthread_mutex_lock(&g_lock);

g_backlight = brightness;

err = write_int(LCD_FILE, brightness);

if (g_haveTrackballLight) {

handle_trackball_light_locked(dev);

}

pthread_mutex_unlock(&g_lock);

return err;

}

也就是往文件/sys/class/leds/lcd-backlight/brightness写入亮度值，然后驱动会根据该文件更改背光的亮度。LCD_FILE的路径根据实际情况更改，同时需要在init.rc 修改其权限，使其可写rgb_to_brightness也根据实际更改，比如要直接亮度值控制，那只要获取r,g,b其中的一个值就行了，如：

static int

rgb_to_brightness(struct light_state_t const* state)

{

int color = state->color & 0x000000ff;

return color;

}