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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.javaprivate 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.java1.2 设置亮度
文件：packages/apps/Settings/src/com/android/settings/BrightnessPreference.javapublic 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.javaframeworks/base/core/java/android/os/PowerManager.java2， 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.javapublic 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CC++代码，setLightBrightness_UNCHECKED原型如下：文件：frameworks/base/servicesjavacomandroidserverHardwareService.javavoid 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）;    }