1 获得显示设备信息：

DisplayManagerService 启动后从SurfaceFlinger当中获取到系统默认的Display 与HDMI display的信息。

2 应用程序端指定其应用ContextImpl的Display。

3 应用程序获得Surface和配置Surface，这个surface对应于SurfaceFlinger中的Layer；

WindowManagerService作为一个系统服务，主要管理系统中所有的应用的Window。在WMS中，每个Window都有一个对应的WindowState对象。

3.1 addWindow,该函数在WindowManagerService当中，由WindowManagerImpl中的addView函数调用到，并且将Window所在的Display作为参数带到WMS当中。

关键是WindowManagerImpl的mContext，从这个mContext获取displayId

3.2在addWindow函数，WMS首先找到窗口所在的Display，创建WindowState，然后将窗口加到Display中的Windowlist当中。win.mToken.addWindow(win); 

3.3 WindowState,获取对应Display的layerstack将其放置在WindowStateAnimator当中，并且将值设置到SurfaceFlinger当中与之对应的Layer中，告知SurfaceFlinger自己所在Display。mSurfaceControl.setLayerStack(mLayerStack);

4 绘制Surface

SurfaceFlinger作为Android在native层比较重要的一个系统服务，主要作用是compose所有的layer，将其绘制输出到显示设备当中，也就是物理Display当中。

SurfaceFlinger根据Layer当中的layerStack成员，获知需要将该Layer绘制到具体哪一个Display当中。

@frameworks/base/core/java/android/app/ActivityThread.java
ActivityThread.performLaunchActivity()
@frameworks/base/core/java/android/app/Activity.javaactivity.attach(appContext, this, getInstrumentation(), r.token, r.ident, app, r.intent, r.activityInfo, title, r.parent, config,r.referrer, r.voiceInteractor, window,);mWindow = new PhoneWindow(this, window, activityConfigCallback);
@frameworks/base/core/java/com/android/internal/policy/PhoneWindow.javamContext = context;  //PhoneWindow设置mContext为Activity里的contextmWindow.setWindowManager((WindowManager)context.getSystemService(Context.WINDOW_SERVICE), mToken, (info.flags & ActivityInfo.FLAG_HARDWARE_ACCELERATED) != 0);//context是attach传入的值，使用context创建WindowManagerif (wm == null) {  //如果wm为空则创建使用mContext创建WindowManager，mContext是PhoneWindow保存的值wm = (WindowManager)mContext.getSystemService(Context.WINDOW_SERVICE);}mWindowManager = ((WindowManagerImpl)wm).createLocalWindowManager(this);return new WindowManagerImpl(mContext, parentWindow, mWindowContextToken); //创建WindowManagerImpl，mContext是wm的，wm有两种情况mContext = context;mParentWindow = parentWindow;1. Activity 为例来分析应用窗口的添加过程
@frameworks/base/core/java/android/app/ActivityThread.java
handleResumeActivity
@frameworks/base/core/java/android/view/WindowManagerImpl.javaView decor = r.window.getDecorView();wm.addView(decor, l);mGlobal.addView(view, params, mContext.getDisplayNoVerify(), mParentWindow, mContext.getUserId());    //WindowManagerImpl的mContext2. 直接添加view
@MyApplication/app/src/main/java/com/example/myapplication/MainActivity.java
TextView textView = new TextView(this);  // context传入this，this是当前的MainActivity
Log.d(TAG, "MyService onCreate: startActivityAsUser, thisContext=" + this.toString());
textView.setText("MyService");
WindowManager.LayoutParams layoutParams = new WindowManager.LayoutParams();
layoutParams.type = WindowManager.LayoutParams.TYPE_KEYGUARD_DIALOG;
layoutParams.width = WindowManager.LayoutParams.WRAP_CONTENT;
layoutParams.height = WindowManager.LayoutParams.WRAP_CONTENT;
windowManager.addView(textView, layoutParams);mGlobal.addView(view, params, mContext.getDisplayNoVerify(), mParentWindow, mContext.getUserId());    //WindowManagerImpl的mContextaddView流程：
@frameworks/base/core/java/android/view/WindowManagerGlobal.java
mGlobal.addView(view, params, mContext.getDisplayNoVerify(), mParentWindow, mContext.getUserId());  //void addView(View view, ViewGroup.LayoutParams params, Display display, Window parentWindow, int userId)root = new ViewRootImpl(view.getContext(), display);
@frameworks/base/core/java/android/view/ViewRootImpl.javaroot.setView(view, wparams, panelParentView, userId);requestLayout();mWindowSession.addToDisplayAsUser(mWindow, mWindowAttributes, mDisplay.getDisplayId());  // mDisplay是addView的时候传入的display