android 屏幕亮度调节方法详解

屏幕亮度自动调节：
主要是从sensor分析之中分离出来分析light 光线感应器，因此就分析一下自动调节屏幕亮度（手机随着光线的强度自我调节，也就是在亮的光线下屏幕自动调亮一些，暗的时候就自动调暗一些，省得光线对眼睛有刺激）.....

    (本人从历经挫折才大概了解流程)，现在就开始讲一下流程，如果有不对地方希望牛人指出来。。。

    先从sttings入手吧，在diaplay中有屏幕亮度调节，有一个进度调，上面有一个checkbox（自动调节屏幕亮度的），

那么我们当然去找settings下的文件开始看了，先找到
diaplaysettings.java文件以及display_setting.xml文件，display_setting.xml里面能找到相应的组件，但是 在diaplaysettings.java文件中却不能找到调用相应组件的代码，

那么我们再到settings中去找，能找到brightnesspreference.java文件，没错这个文件就是自动调节亮度的文件，我们先看看代码：
构造函数中有mautomaticavailable = context.getresources().getboolean(com.android.internal.r.bool.config_automatic_brightness_available);
开始以为mautomaticavailabl的值（为true，在config.xml中）是判断是否自动调节亮度，因为在我跟进到powermanagerservice.java中，在initinthread() 中
  musesoftwareautobrightness = resources.getboolean(
                com.android.internal.r.bool.config_automatic_brightness_available);

        if (musesoftwareautobrightness) {
            mautobrightnesslevels = resources.getintarray(
                    com.android.internal.r.array.config_autobrightnesslevels);//得到自动化调节的值调用 getautobrightnessvalue(int sensorvalue, int[] values) 方法
            mlcdbacklightvalues = resources.getintarray(
                    com.android.internal.r.array.config_autobrightnesslcdbacklightvalues);
            mbuttonbacklightvalues = resources.getintarray(
                    com.android.internal.r.array.config_autobrightnessbuttonbacklightvalues);
            mkeyboardbacklightvalues = resources.getintarray(。。。。。
。。。。。。这里看起来好像是当musesoftwareautobrightness为true时就取得config.xml文件config_autobrightnesslevels的值，再去根据光线自动调节，但是mautomaticavailabl的值只是说明有没有自动调节屏幕的功能（比如说你将config.xml文件的config_automatic_brightness_available的值改为false，编译替换framework-res.apk那么在屏幕亮度调节中将没有自动调节的checkbox），这也能解释构造函数一开始就初始化mautomaticavailabl的值。

接下来在brightnesspreference.java文件中有onprogresschanged，onstarttrackingtouch(seekbar seekbar)，onstoptrackingtouch(seekbar seekbar)方法，这些一看也能懂就不介绍了，在onbinddialogview(view view)方法中有
mcheckbox = (checkbox)view.findviewbyid(r.id.automatic_mode);
        if (mautomaticavailable) {//当有自动调节功能
            mcheckbox.setoncheckedchangelistener(this);//为checkbox添加监听事件
            try {
                moldautomatic = settings.system.getint(getcontext().getcontentresolver(),
                        settings.system.screen_brightness_mode);
。。。。。。
主要看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);
        }
    }
这里才是你选择自动调节亮度的checkbox，如果选择则setmode（settings.system.screen_brightness_mode_automatic）；并将数据存放到中。

这里是重点：这里有个数据库，当监测到数据库中的值发生改变时也就是变为settings.system.screen_brightness_mode_automatic时，就会跳到
powermanagerservice.java的initinthread()中contentresolver resolver = mcontext.getcontentresolver();
        cursor settingscursor = resolver.query(settings.system.content_uri, null,
                "(" + settings.system.name + "=?) or ("
                        + settings.system.name + "=?) or ("
                        + settings.system.name + "=?) or ("
                        + settings.system.name + "=?) or ("
                        + settings.system.name + "=?) or ("
                        + settings.system.name + "=?) or ("
                        + settings.system.name + "=?)",
                new string[]{stay_on_while_plugged_in, screen_off_timeout, dim_screen, xec_dls_control,
                        screen_brightness_mode, window_animation_scale, transition_animation_scale},
                null);
        msettings = new contentquerymap(settingscursor, settings.system.name, true, mhandler);
        settingsobserver settingsobserver = new settingsobserver();
        msettings.addobserver(settingsobserver);
数据库中数据发生改变时触发事件的发生。

在 powermanagerservice.java的systemready()（只在开机调用一次就不再调用）中
 if (musesoftwareautobrightness) {
            log.i("frist","frist="+"aaaa");
            mlightsensor = msensormanager.getdefaultsensor(sensor.type_light);
            enablelightsensor(true);
        }
而musesoftwareautobrightness是在initinthread()线程中取得了true值，那么就到enablelightsensor(true);方法去看
 if (enable) {
                    msensormanager.registerlistener(mlightlistener, mlightsensor,
                            sensormanager.sensor_delay_normal);
                }
如果传递来的值为true也就是enable=true就监听而且用匹配屏幕方向变化的感应sensor_delay_normal。
再看mlightlistener事件：sensoreventlistener mlightlistener = new sensoreventlistener() {
        public void onsensorchanged(sensorevent event) {
            synchronized (mlocks) {
                int value = (int)event.values[0];//从event里面获取当前数据
                log.i("value","value="+value);       
                long milliseconds = systemclock.elapsedrealtime();
                if (mdebuglightsensor) {
                    slog.d(tag, "onsensorchanged: light value: " + value);
                }
                mhandler.removecallbacks(mautobrightnesstask);
                if (mlightsensorvalue != value) {//mlightsensorvalue是当前的屏幕亮度
                    if (mlightsensorvalue == -1 ||
                            milliseconds < mlastscreenontime + mlightsensorwarmuptime) {
                        // process the value immediately if screen has just turned on
                        lightsensorchangedlocked(value);
                    } else {
                        // delay processing to debounce the sensor
                        mlightsensorpendingvalue = value;//mlightsensorpendingvalue是准备要设置的亮度
                        mhandler.postdelayed(mautobrightnesstask, light_sensor_delay);//到mautobrightnesstask线程去完成自动调节
                    }
                } else {
                    mlightsensorpendingvalue = -1;
                }
            }
        }
当前屏幕亮度肯定不等与-1，所以做else中的mhandler.postdelayed(mautobrightnesstask, light_sensor_delay)，那么我们再到mautobrightnesstask
线程看：private runnable mautobrightnesstask = new runnable() {
        public void run() {
            synchronized (mlocks) {
                int value = (int)mlightsensorpendingvalue;
                log.i("mlightsensorpendingvalue","mlightsensorpendingvalue"+mlightsensorpendingvalue);
                if (value >= 0) {
                    mlightsensorpendingvalue = -1;
                    lightsensorchangedlocked(value);
                }
            }
        }
    };就是不断的去调用lightsensorchangedlocked(value)
private void lightsensorchangedlocked(int value) {
。。。。。。。
if (mlightsensorvalue != value) {
            mlightsensorvalue = value;
            if ((mpowerstate & battery_low_bit) == 0) {
                // use light sensor value no matter it is in a dock or not.
                int lcdvalue = getautobrightnessvalue(
                        value,
                        mlcdbacklightvalues);// 取得mlcdbacklightvalues里面的值
                int buttonvalue = getautobrightnessvalue(value, mbuttonbacklightvalues);
                int keyboardvalue;
                if (mkeyboardvisible) {
                    keyboardvalue = getautobrightnessvalue(value, mkeyboardbacklightvalues);
                } else {
                    keyboardvalue = 0;
                }
。。。
if (mautobrightessenabled && mscreenbrightnessoverride < 0) {//设置屏幕亮度
                    mscreenbrightness.settargetlocked(lcdvalue, autobrightness_anim_steps,
                            initial_screen_brightness, (int)mscreenbrightness.curvalue);
                }
。。。。。
   }