Handle onto a raw buffer that is being managed by the screen compositor.
A Surface is generally created by or from a consumer of image buffers (such as a SurfaceTexture, android.media.MediaRecorder, or android.renderscript.Allocation), and is handed to some kind of producer (such as OpenGL, MediaPlayer, or CameraDevice) to draw into.
Note: A Surface acts like a weak reference to the consumer it is associated with. By itself it will not keep its parent consumer from being reclaimed.

Override  
public Activity handleLaunchActivity(ActivityClientRecord r,  
        PendingTransactionActions pendingActions, Intent customIntent) {
	...
	WindowManagerGlobal.initialize();
	...
	final Activity a = performLaunchActivity(r, customIntent);
}


private Activity performLaunchActivity(ActivityClientRecord r, Intent customIntent) {
	...
	ContextImpl appContext = createBaseContextForActivity(r);
	...
	Activity activity = null;
	activity = mInstrumentation.newActivity(  
        cl, component.getClassName(), r.intent);
		
	...
	Application app = r.packageInfo.makeApplication(false, mInstrumentation);
	...
	activity.attach(appContext, this, getInstrumentation(), r.token,  
        r.ident, app, r.intent, r.activityInfo, title, r.parent,  
        r.embeddedID, r.lastNonConfigurationInstances, config,  
        r.referrer, r.voiceInteractor, window, r.configCallback,  
        r.assistToken, r.shareableActivityToken);
		
	...
	mInstrumentation.callActivityOnCreate(activity, r.state);
}

final void attach(Context context, ActivityThread aThread,  
        Instrumentation instr, IBinder token, int ident,  
        Application application, Intent intent, ActivityInfo info,  
        CharSequence title, Activity parent, String id,  
        NonConfigurationInstances lastNonConfigurationInstances,  
        Configuration config, String referrer, IVoiceInteractor voiceInteractor,  
        Window window, ActivityConfigCallback activityConfigCallback, IBinder assistToken,  
        IBinder shareableActivityToken) {
	
	attachBaseContext(context);  
  
	mFragments.attachHost(null /*parent*/);
	...
	mWindow = new PhoneWindow(this, window, activityConfigCallback);
	...
	mWindow.setWindowManager(  
        (WindowManager)context.getSystemService(Context.WINDOW_SERVICE),  
        mToken, mComponent.flattenToString(),  
        (info.flags & ActivityInfo.FLAG_HARDWARE_ACCELERATED) != 0);  
	if (mParent != null) {  
    	mWindow.setContainer(mParent.getWindow());  
	}  
	mWindowManager = mWindow.getWindowManager();

}

public void setWindowManager(WindowManager wm, IBinder appToken, String appName,  
        boolean hardwareAccelerated) {  
    mAppToken = appToken;  
    mAppName = appName;  
    mHardwareAccelerated = hardwareAccelerated;  
    if (wm == null) {  
        wm = (WindowManager)mContext.getSystemService(Context.WINDOW_SERVICE);  
    }  
    mWindowManager = ((WindowManagerImpl)wm).createLocalWindowManager(this);  
}


//WindowManagerImpl.java
public WindowManagerImpl createLocalWindowManager(Window parentWindow) {  
    Bridge.getLog().fidelityWarning(ILayoutLog.TAG_UNSUPPORTED,  
            "The preview does not support multiple windows.",  
            null, null, null);  
    return this;  
}

//ActivityThread.java
public void handleResumeActivity(ActivityClientRecord r, boolean finalStateRequest,  
        boolean isForward, String reason) {
	if (r.activity.mVisibleFromClient) {  
    	r.activity.makeVisible();  
	}
}



//Activity.java
void makeVisible() {  
    if (!mWindowAdded) {  
        ViewManager wm = getWindowManager();  
        wm.addView(mDecor, getWindow().getAttributes());  
        mWindowAdded = true;  
    }  
    mDecor.setVisibility(View.VISIBLE);  
}

//WindowmanagerGlobal
public void addView(View view, ViewGroup.LayoutParams params,  
        Display display, Window parentWindow, int userId) {
	ViewRootImpl root = new ViewRootImpl(view.getContext(), display);
	root.setView(view, wparams, panelParentView, userId);
}



//ViewRootImpl
public void setView(View view, WindowManager.LayoutParams attrs, View panelParentView,  
        int userId) {
	//启动Choreographer的Vsync信号监听，
	requestLayout();
	//通过WindowSession请求wms，这里的WindowSession是一个binder接口。
	es = mWindowSession.addToDisplayAsUser(mWindow, mWindowAttributes,  
        getHostVisibility(), mDisplay.getDisplayId(), userId,  
        mInsetsController.getRequestedVisibility(), inputChannel, mTempInsets,  
        mTempControls);
		
}


//WindowSession初始化
public static IWindowSession getWindowSession() {  
    synchronized (WindowManagerGlobal.class) {  
        if (sWindowSession == null) {  
            try {  
                // Emulate the legacy behavior.  The global instance of InputMethodManager  
 // was instantiated here. // TODO(b/116157766): Remove this hack after cleaning up @UnsupportedAppUsage InputMethodManager.ensureDefaultInstanceForDefaultDisplayIfNecessary();  
                IWindowManager windowManager = getWindowManagerService();  
                sWindowSession = windowManager.openSession(  
                        new IWindowSessionCallback.Stub() {  
                            @Override  
 public void onAnimatorScaleChanged(float scale) {  
                                ValueAnimator.setDurationScale(scale);  
                            }  
                        });  
            } catch (RemoteException e) {  
                throw e.rethrowFromSystemServer();  
            }  
        }  
        return sWindowSession;  
    }  
}

//Session.java   Session是IWindowSession这个AIDL接口的实现类，是应用与WMS进行交互的接口
@Override  
public int addToDisplay(IWindow window, WindowManager.LayoutParams attrs,  
        int viewVisibility, int displayId, InsetsState requestedVisibility,  
        InputChannel outInputChannel, InsetsState outInsetsState,  
        InsetsSourceControl[] outActiveControls) {  
    return mService.addWindow(this, window, attrs, viewVisibility, displayId,  
            UserHandle.getUserId(mUid), requestedVisibility, outInputChannel, outInsetsState,  
            outActiveControls);  
}

//1.WindowManagerService.addWindow()
public int addWindow(Session session, IWindow client, LayoutParams attrs, int viewVisibility,  
        int displayId, int requestUserId, InsetsState requestedVisibility,  
        InputChannel outInputChannel, InsetsState outInsetsState,  
        InsetsSourceControl[] outActiveControls) {
	final DisplayContent displayContent = getDisplayContentOrCreate(displayId, attrs.token);
	WindowToken token = displayContent.getWindowToken(  
        hasParent ? parentWindow.mAttrs.token : attrs.token);
	if (token == null) {
		token = new WindowToken.Builder(this, binder, type)  
        .setDisplayContent(displayContent)  
        .setOwnerCanManageAppTokens(session.mCanAddInternalSystemWindow)  
        .setRoundedCornerOverlay(isRoundedCornerOverlay)  
        .build();
	}
	final WindowState win = new WindowState(this, session, client, token, parentWindow,  
        appOp[0], attrs, viewVisibility, session.mUid, userId,  
        session.mCanAddInternalSystemWindow);
		
	...
	win.attach();
	
}

//2.WindowSession.attach()
void attach() {  
    mSession.windowAddedLocked();  
}

//3.Session.windowAddedLocked()
 void windowAddedLocked(){
 	...
 	mSurfaceSession = new SurfaceSession();
 	...
 }
 
 //4.SurfaceSession
 public SurfaceSession() {  
    mNativeClient = nativeCreate();  
}


5.android_view_SurfaceSession.nativeCreate()
static jlong nativeCreate(){
	SurfaceClientComposer* client = new SurfaceClientComposer();
}