接animate()的openSurfaceTransaction(),prepareSurfaces(),closeSurfaceTransaction()

1. mService.openSurfaceTransaction()，通过SurfaceControl来通知native开始一个Transaction；

2. mService.closeSurfaceTransaction()，通过SurfaceControl来通知native(SurfaceFlinger)关闭一个Transaction最终来执行合成显示等工作；

WMS#openSurfaceTransaction：New出GlobalTransactionWrapper 接animate()的dc.prepareSurfaces();

DisplayContent#prepareSurfaces：将SurfaceControl提交在了mPendingTransaction上。然后完成遍历后，将mPendingTransaction合并到全局Transaction对象上提交给SurfaceFlinger。

mergeToGlobalTransaction将提供的Transaction合并提交,然后接animate()调Wms的closeSurfaceTransaction()

WMS#closeSurfaceTransaction: 再调用SurfaceControl的内部类GlobalTransactionWrapper#applyGlobalTransaction

SurfaceComposerClient#apply: 再调用android_view_SurfaceControl.cpp的nativeApplyTransaction方法,

apply方法主要就是收集之前通过transaction属性设置方法设置所有信息都需要收集起来，比如最重要的composerStates，然后调用sf的跨进程方法setTransactionState传递到sf中。

@frameworks/base/services/core/java/com/android/server/wm/WindowAnimator.java
private void animate(long frameTimeNs) {
@frameworks/base/services/core/java/com/android/server/wm/WindowManagerService.java    
    mService.openSurfaceTransaction();
@frameworks/base/core/java/android/view/SurfaceControl.java
        SurfaceControl.openTransaction();
            sGlobalTransaction = new GlobalTransactionWrapper();
@frameworks/base/services/core/java/com/android/server/wm/DisplayContent.java
    dc.prepareSurfaces();
@frameworks/base/core/java/android/view/SurfaceControl.java    
        SurfaceControl.mergeToGlobalTransaction(transaction);
            sGlobalTransaction.merge(t);
@frameworks/base/core/jni/android_view_SurfaceControl.cpp            
                nativeMergeTransaction(mNativeObject, other.mNativeObject);
                    transaction->merge(std::move(*otherTransaction));
    mService.closeSurfaceTransaction("WindowAnimator");
@frameworks/base/core/java/android/view/SurfaceControl.java    
        SurfaceControl.closeTransaction();
            else if (--sTransactionNestCount > 0) { //open和close一一对应，保证 sTransactionNestCount 数量    
            sGlobalTransaction.applyGlobalTransaction(false);
@frameworks/base/core/jni/android_view_SurfaceControl.cpp
                nativeApplyTransaction(mNativeObject, sync);
@frameworks/native/libs/gui/SurfaceComposerClient.cpp                
                    transaction->apply(sync);
                        for (auto const& kv : mComposerStates){ composerStates.add(kv.second);  }  // 遍历mComposerStates，其中包含了所有的InputWindow
                        displayStates = std::move(mDisplayStates);
                            //最后把上面收集的Transaction相关信息，调用sf的setTransactionState进行跨进程传递到sf进程
                            sf->setTransactionState(mFrameTimelineInfo, composerStates, displayStates, flags, applyToken,mInputWindowCommands, mDesiredPresentTime, mIsAutoTimestamp,hasListenerCallbacks, listenerCallbacks, mId)
                            clear();//apply后就需要把Transaction进行clear