SufraceFlinger图像合成原理(2)-SurfaceFlinger与应用进程间的通信

SF提供与其他进程通信的两个Binder : ISurfaceComposer、ISurfaceComposerClient。

每个应用进程会创建一个SurfaceComposerClient对象，用于和SF通信SurfaceComposerClient实例创建后调用onFirstRef

/frameworks/native/libs/gui/SurfaceComposerClient.cpp

ini 复制代码

void SurfaceComposerClient::onFirstRef() {
    // 1.
    sp<ISurfaceComposer> sf(ComposerService::getComposerService());
    if (sf != nullptr && mStatus == NO_INIT) {
        sp<ISurfaceComposerClient> conn;
        // 2. 
        conn = sf->createConnection();
        if (conn != nullptr) {
            mClient = conn;
            mStatus = NO_ERROR;
        }
    }
}

onFirstRef中获取了ISurfaceComposer和ISurfaceComposerClient两个binder的代理对象

通过ServiceManager获取SurfaceFlinger 服务代理对象
1. ComposerService::getComposerService()
2. -> ComposerService::getInstance().connectLocked()
3. /frameworks/native/libs/gui/SurfaceComposerClient.cpp

arduino 复制代码

68  bool ComposerService::connectLocked() {
69      const String16 name("SurfaceFlinger");
        //waitForService是通过ServiceManager获取系统服务
70      mComposerService = waitForService<ISurfaceComposer>(name);
71      if (mComposerService == nullptr) {
72          return false; // fatal error or permission problem
73      }
74  
        ... ...
90  }

通过sf->createConnection()，获取ISurfaceComposerClient代理对象

/frameworks/native/libs/gui/ISurfaceComposer.cpp

kotlin 复制代码

class BpSurfaceComposer : public BpInterface<ISurfaceComposer>
{
  virtual sp<ISurfaceComposerClient> createConnection(){
      Parcel data, reply;
      data.writeInterfaceToken(ISurfaceComposer::getInterfaceDescriptor());
      remote()->transact(BnSurfaceComposer::CREATE_CONNECTION, data, &reply);
      return interface_cast<ISurfaceComposerClient>(reply.readStrongBinder());
  }       

}

调用到服务端BnSurfaceComposer

css 复制代码

status_t BnSurfaceComposer::onTransact(
  uint32_t code, const Parcel& data, Parcel* reply, uint32_t flags){
  switch(code) {
      case CREATE_CONNECTION: {
          CHECK_INTERFACE(ISurfaceComposer, data, reply);
          sp<IBinder> b = IInterface::asBinder(createConnection());
          reply->writeStrongBinder(b);
          return NO_ERROR;
    ... ...

最后在SurfaceFlinger 中会创建一个Client对象，即BnSurfaceComposerClient对象，所以每个应用进程在SurfaceFlinger中都有一个Client对象与之对应

/frameworks/native/services/surfaceflinger/SurfaceFlinger.cpp

arduino 复制代码

522  sp<ISurfaceComposerClient> SurfaceFlinger::createConnection() {
523      const sp<Client> client = new Client(this);
524      return client->initCheck() == NO_ERROR ? client : nullptr;
525  }

Client对象持有SurfaceFlinger的引用

kotlin 复制代码

class Client : public BnSurfaceComposerClient
{
    ... ...
    sp<SurfaceFlinger> mFlinger;
}

到此涉及到的类关系图如下：

ISurfaceComposer：应用端与SurfaceFlinger 通信，主要是SurfaceFlinger提供的各种操作，如 setTransactionState更新状态去触发合成
ISurfaceComposerClient：应用端与SurfaceFlinger进程的Client通信，主要是是layer 相关操作，如createLayer 等