Android Camera 系统架构源码分析(3)---->Camera的显示流程

2023年10月4日 244次阅读来源: Android源码分析

Preview的显示流程
这次我们要从最开始startPreview的时候开始，在starPreview之间就setPreviewWindow()。

    
 
     
  //CameraClient.cpp
     
  status_t CameraClient::startPreviewMode() {
     
   mHardware->previewEnabled();
     
   mHardware->setPreviewWindow(mPreviewWindow);
     
   result = mHardware->startPreview();
     
  }

最后会调用到Cam1DeviceBase的setPreviewWindow()，其中的调用过程和startPreview()的一样，不再赘述

     
 
      
  Cam1DeviceBase::setPreviewWindow(preview_stream_ops* window)
      
  {
      
   //(1) 初始化显示
      
   status_t status = initDisplayClient(window);
      
   
      
   //(2) 开始显示
      
   status = enableDisplayClient();
      
  
      
  }

initDisplayClient(); 在之前说的Cam1DeviceBase::startPreview()的(2)也调用了
initDisplayClient();

    
 
     
  Cam1DeviceBase::initDisplayClient(preview_stream_ops* window)
     
  {
     
   Size previewSize;
     
  
     
   // [1] Check to see whether the passed window is NULL or not.
     
   //...
     
  
     
   // [2] Get preview size. 获得预览参数
     
   queryPreviewSize(previewSize.width, previewSize.height);
     
  
     
   // [3] Initialize Display Client.
     
   // [3.1] create a Display Client. 仅是初始化变量
     
   mpDisplayClient = IDisplayClient::createInstance();
     
  
     
   // [3.2] initialize the newly-created Display Client.
     
   mpDisplayClient->init();
     
  
     
   // [3.3] set preview_stream_ops & related window info.
     
   mpDisplayClient->setWindow(window, previewSize.width, previewSize.height, queryDisplayBufCount());
     
  
     
   // [3.4] set Image Buffer Provider Client if it exist.
     
   mpCamAdapter != 0 && ! mpDisplayClient->setImgBufProviderClient(mpCamAdapter);
     
  }

下面是
initDisplayClient();的细节分析

    
 
     
  DisplayClient::init()
     
  { 
     
   /**
     
   构造DisplayThread并让它run起来，注意构造时传入的handle参数为dispalyClient
     
   构造ImgBufQueue,它的id为eID_DISPLAY
     
   在previewClient init()时，也创建了一个ImgBufQueue，而ID是eID_PRV_CB
     
   **/
     
   ret = createDisplayThread() && createImgBufQueue();
     
  }
     
  
     
  DisplayClient::setWindow(preview_stream_ops*const window, int32_t const wndWidth, 
     
   int32_t const wndHeight, int32_t const i4MaxImgBufCount)
     
  { return set_preview_stream_ops(window, wndWidth, wndHeight, i4MaxImgBufCount);
     
  }
     
  
     
  DisplayClient::set_preview_stream_ops(preview_stream_ops*const window, int32_t const wndWidth, 
     
   int32_t const wndHeight, int32_t const i4MaxImgBufCount)
     
  {
     
   int32_t min_undequeued_buf_count = 0;
     
   //
     
   // (2) Check
     
   //....
     
   // (3) Sava info.
     
   mpStreamImgInfo.clear();
     
   mpStreamImgInfo = new ImgInfo(wndWidth, wndHeight, CAMERA_DISPLAY_FORMAT, CAMERA_DISPLAY_FORMAT_HAL, "Camera@Display");
     
   mpStreamOps = window;
     
   mi4MaxImgBufCount = i4MaxImgBufCount;
     
  
     
   // (4.1) Set gralloc usage bits for window. 
     
   err = mpStreamOps->set_usage(mpStreamOps, CAMERA_GRALLOC_USAGE);
     
  
     
   // (4.2) Get minimum undequeue buffer count
     
   err = mpStreamOps->get_min_undequeued_buffer_count(mpStreamOps, &min_undequeued_buf_count);
     
  
     
   // (4.3) Set the number of buffers needed for display.
     
   err = mpStreamOps->set_buffer_count(mpStreamOps, mi4MaxImgBufCount+min_undequeued_buf_count);
     
  
     
   // (4.4) Set window geometry
     
   err = mpStreamOps->set_buffers_geometry(mpStreamOps, mpStreamImgInfo->mu4ImgWidth, 
     
   mpStreamImgInfo->mu4ImgHeight, mpStreamImgInfo->mi4ImgFormat);
     
  }
     
  
     
  DisplayClient::setImgBufProviderClient(sp<IImgBufProviderClient>const& rpClient)
     
  {
     
   rpClient->onImgBufProviderCreated(mpImgBufQueue);
     
   
     
   mpImgBufPvdrClient = rpClient;
     
  }
     
  
     
  //BaseCamAdapter.cpp
     
  BaseCamAdapter::onImgBufProviderCreated(sp<IImgBufProvider>const& rpProvider)
     
  {
     
   int32_t const i4ProviderId = rpProvider->getProviderId();
     
  
     
   mpImgBufProvidersMgr->setProvider(i4ProviderId, rpProvider);
     
  }

DispalyClient的初始化就这么完成了，从但是我们并不知道上面已经初始化的参数有什么作用，又是如何开始刷显示的呢？我们返回到enableDisplayClient()继续跟踪

    
 
     
  Cam1DeviceBase::enableDisplayClient()
     
  {
     
   Size previewSize;
     
   
     
   // [1] Get preview size. 获取预览参数
     
   queryPreviewSize(previewSize.width, previewSize.height);
     
  
     
   // [2] Enable
     
   mpDisplayClient->enableDisplay(previewSize.width, previewSize.height, queryDisplayBufCount(), mpCamAdapter);
     
  }

    
 
     
  Cam1DeviceBase::enableDisplayClient()
     
  {
     
   Size previewSize;
     
   
     
   // [1] Get preview size. 获取预览参数
     
   queryPreviewSize(previewSize.width, previewSize.height);
     
  
     
   // [2] Enable
     
   mpDisplayClient->enableDisplay(previewSize.width, previewSize.height, queryDisplayBufCount(), mpCamAdapter);
     
  }
     
  
     
  DisplayClient::enableDisplay(int32_t const i4Width, int32_t const i4Height, 
     
   int32_t const i4BufCount, sp<IImgBufProviderClient>const& rpClient)
     
  {
     
   // Enable.
     
   enableDisplay();
     
  
     
  }
     
  
     
  DisplayClient::enableDisplay()
     
  {
     
   //Post a command to wake up the thread. 向DisplayThread发送消息
     
   mpDisplayThread->postCommand(Command(Command::eID_WAKEUP));
     
  }
     
  
     
  DisplayThread::threadLoop()
     
  {
     
   Command cmd;
     
   if ( getCommand(cmd) )
     
   {
     
   switch (cmd.eId)
     
   {
     
   case Command::eID_EXIT:
     
   //....
     
   case Command::eID_WAKEUP:
     
   default:
     
   //调用的是handler的onThreadloop
     
   //在前面已知DisplayThread的handler被设置成了DisplayClient
     
   mpThreadHandler->onThreadLoop(cmd);
     
   break;
     
   }
     
   }
     
  }

DisplayClient的onThreadLoop()在DisplayClient.BufOps.cpp里，仔细观察下面的函数是不会有似曾相识的感觉，原来下面函数的结构和Preview的onClientThreadLoop的函数结构一模一样，边里面使用的函数名都一样，虽然不是同一个函数

    
 
     
  DisplayClient::onThreadLoop(Command const& rCmd)
     
  {
     
   // (0) lock Processor.
     
   sp<IImgBufQueue> pImgBufQueue;
     
  
     
   // (1) Prepare all TODO buffers. 准备buf，把buf放入队列里
     
   if ( ! prepareAllTodoBuffers(pImgBufQueue) )
     
   {
     
   return true;
     
   }
     
  
     
   // (2) Start 通知开始处理
     
   pImgBufQueue->startProcessor();
     
  
     
   // (3) Do until disabled.
     
   while ( 1 )
     
   {
     
   // (.1) 阻塞等待通知，并开始处理buf
     
   waitAndHandleReturnBuffers(pImgBufQueue);
     
  
     
   // (.2) break if disabled.
     
   if ( ! isDisplayEnabled() )
     
   {
     
   MY_LOGI("Display disabled");
     
   break;
     
   }
     
  
     
   // (.3) re-prepare all TODO buffers, if possible, 
     
   // since some DONE/CANCEL buffers return. 准备buf，把buf放入队列里
     
   prepareAllTodoBuffers(pImgBufQueue);
     
   }
     
   //
     
   // (4) Stop
     
   pImgBufQueue->pauseProcessor();
     
   pImgBufQueue->flushProcessor();
     
   pImgBufQueue->stopProcessor();
     
   //
     
   // (5) Cancel all un-returned buffers.
     
   cancelAllUnreturnBuffers();
     
   //
     
   {
     
   Mutex::Autolock _l(mStateMutex);
     
   mState = eState_Suspend;
     
   mStateCond.broadcast();
     
   }
     
  }

根据之前的经验很直觉地找到了waitAndHandleReturnBuffers()函数，正是里面处理了数据，但是又怎么样把数据显示出来的呢？继续看

    
 
     
  DisplayClient::waitAndHandleReturnBuffers(sp<IImgBufQueue>const& rpBufQueue)
     
  {
     
   Vector<ImgBufQueNode> vQueNode;
     
  
     
   // (1) deque buffers from processor. 阻塞等待通知读取Buf
     
   rpBufQueue->dequeProcessor(vQueNode);
     
   
     
   // (2) handle buffers dequed from processor.
     
   ret = handleReturnBuffers(vQueNode);
     
  }
     
  
     
  DisplayClient::handleReturnBuffers(Vector<ImgBufQueNode>const& rvQueNode)
     
  {
     
   /*
     
   * Notes:
     
   * For 30 fps, we just enque (display) the latest frame, 
     
   * and cancel the others.
     
   * For frame rate > 30 fps, we should judge the timestamp here or source.
     
   */
     
   
     
   //
     
   // (3) Remove from List and enquePrvOps/cancelPrvOps, one by one.
     
   int32_t const queSize = rvQueNode.size();
     
   for (int32_t i = 0; i < queSize; i++)
     
   {
     
   sp<IImgBuf>const& rpQueImgBuf = rvQueNode[i].getImgBuf(); // ImgBuf in Queue.
     
   sp<StreamImgBuf>const pStreamImgBuf = *mStreamBufList.begin(); // ImgBuf in List.
     
   // (.1) Check valid pointers to image buffers in Queue & List
     
   if ( rpQueImgBuf == 0 || pStreamImgBuf == 0 )
     
   {
     
   MY_LOGW("Bad ImgBuf:(Que[%d], List.begin)=(%p, %p)", i, rpQueImgBuf.get(), pStreamImgBuf.get());
     
   continue;
     
   }
     
   // (.2) Check the equality of image buffers between Queue & List.
     
   if ( rpQueImgBuf->getVirAddr() != pStreamImgBuf->getVirAddr() )
     
   {
     
   MY_LOGW("Bad address in ImgBuf:(Que[%d], List.begin)=(%p, %p)", i, rpQueImgBuf->getVirAddr(), pStreamImgBuf->getVirAddr());
     
   continue;
     
   }
     
   // (.3) Every check is ok. Now remove the node from the list.
     
   mStreamBufList.erase(mStreamBufList.begin());
     
   //
     
   // (.4) enquePrvOps/cancelPrvOps
     
   if ( i == idxToDisp ) {
     
  
     
   //
     
   if(mpExtImgProc != NULL)
     
   {
     
   if(mpExtImgProc->getImgMask() & ExtImgProc::BufType_Display)
     
   {
     
   IExtImgProc::ImgInfo img;
     
   //
     
   img.bufType = ExtImgProc::BufType_Display;
     
   img.format = pStreamImgBuf->getImgFormat();
     
   img.width = pStreamImgBuf->getImgWidth();
     
   img.height = pStreamImgBuf->getImgHeight();
     
   img.stride[0] = pStreamImgBuf->getImgWidthStride(0);
     
   img.stride[1] = pStreamImgBuf->getImgWidthStride(1);
     
   img.stride[2] = pStreamImgBuf->getImgWidthStride(2);
     
   img.virtAddr = (MUINT32)(pStreamImgBuf->getVirAddr());
     
   img.bufSize = pStreamImgBuf->getBufSize();
     
   //预留的处理接口，用户可自行填充
     
   mpExtImgProc->doImgProc(img);
     
   }
     
   }
     
   //处理将要显示的Buf
     
   enquePrvOps(pStreamImgBuf);
     
   }
     
   else {
     
   //处理被忽略的buf
     
   cancelPrvOps(pStreamImgBuf);
     
   }
     
   }
     
  }
     
  
     
  DisplayClient::enquePrvOps(sp<StreamImgBuf>const& rpImgBuf)
     
  {
     
   // [1] unlock buffer before sending to display
     
   GraphicBufferMapper::get().unlock(rpImgBuf->getBufHndl());
     
  
     
   // [2] Dump image if wanted.
     
   dumpImgBuf_If(rpImgBuf);
     
  
     
   // [3] set timestamp.
     
   err = mpStreamOps->set_timestamp(mpStreamOps, rpImgBuf->getTimestamp());
     
   
     
   // [4] set gralloc buffer type & dirty 设置buf的参数
     
   ::gralloc_extra_setBufParameter(rpImgBuf->getBufHndl(),
     
   GRALLOC_EXTRA_MASK_TYPE | GRALLOC_EXTRA_MASK_DIRTY, GRALLOC_EXTRA_BIT_TYPE_CAMERA | GRALLOC_EXTRA_BIT_DIRTY);
     
  
     
   // [5] unlocks and post the buffer to display.
     
   //此处我们的mpStreamOps在之前的set_preview_stream_ops()被初始化为window，即setWindow()传下来的window参数。
     
   //所以我们得往上找，这个window是什么东西。
     
   err = mpStreamOps->enqueue_buffer(mpStreamOps, rpImgBuf->getBufHndlPtr());
     
  }

再往回找，setPreviewWindow传入了一个window，这个是一个Surface，这个surface通过App层的Surface传下来的buf重新构建的

     
 
      
  // set the buffer consumer that the preview will use
      
  status_t CameraClient::setPreviewTarget(
      
   const sp<IGraphicBufferProducer>& bufferProducer) {
      
   
      
   sp<IBinder> binder;
      
   sp<ANativeWindow> window;
      
   if (bufferProducer != 0) {
      
   binder = bufferProducer->asBinder();
      
   // Using controlledByApp flag to ensure that the buffer queue remains in
      
   // async mode for the old camera API, where many applications depend
      
   // on that behavior.
      
   window = new Surface(bufferProducer, /*controlledByApp*/ true);
      
   }
      
   return setPreviewWindow(binder, window);
      
  }

setPreviewTarget
()在最开始的
android_hardware_Camera.cpp里被调用，这里传进来的bufferProduce是从App层的surface里面获取出来的一个buf

      
 
       
  static void android_hardware_Camera_setPreviewSurface(JNIEnv *env, jobject thiz, jobject jSurface)
       
  {
       
   sp<IGraphicBufferProducer> gbp;
       
   sp<Surface> surface;
       
  
       
   surface = android_view_Surface_getSurface(env, jSurface);
       
   gbp = surface->getIGraphicBufferProducer();
       
  
       
   if (camera->setPreviewTarget(gbp) != NO_ERROR) {
       
   jniThrowException(env, "java/io/IOException", "setPreviewTexture failed");
       
   }
       
  }

你会以为上面的pStreamOps->enqueue_buffer用的就是这个surface，其实不是，这里又转了一下

      
 
       
  status_t setPreviewWindow(const sp<ANativeWindow>& buf)
       
  {
       
   mPreviewWindow = buf;
       
   mHalPreviewWindow.user = this;
       
  
       
   return mDevice->ops->set_preview_window(mDevice,
       
   buf.get() ? &mHalPreviewWindow.nw : 0);
       
  }

这里判断surface的传下来的buf是否为空，如果不为空则把mHalPreviewWindow.nw传下去，这个nw是一个操作方法的集合。相对应的
enqueue_buffer被初始化为下面这个函数

      
 
       
  static int __enqueue_buffer(struct preview_stream_ops* w,
       
   buffer_handle_t* buffer)
       
  {
       
   ANativeWindow *a = anw(w);
       
   return a->queueBuffer(a,
       
   container_of(buffer, ANativeWindowBuffer, handle), -1);
       
  }

pStreamOps->enqueue_buffer就是执行了一下上面的方法。其实就是把camera里面的数据填进surface的buf队列里

写过APP的都知道，这个Surface是Android上层用于显示的一个辅助类。而Camera的预览也相当于调用了Surface的操作函数。那问题又来了，调用这些Surface是如何去显示的呢？……我就到此为止了，完成了我做知识储备的目的，日后要是工作有需要深入再深入了，有兴趣的朋友可以自行……….深入。我们还是再继续看，这些数据是如何来的呢？

现在回头看看现在涉及到的几个大类做一下总结。
Cam1DeviceBase（包括其子类和父类）包含了所有的Camera的操作函数，如Open，显示，拍照，录像，自动对焦的操作，以及这些Camera操作和Camera硬件涉及到的参数，可以说，Cam1Device对Frameworks及App层来说就是一个Camera了。
在Cam1DeviceBase里包含了ParamsManager，顾名思义就是Camera的参数管理，我们之前也没去理会他，就让它飘会吧。Cam1DeviceBase还包含了几个Client，用于负责所有的功能操作。DisplayClient用来负责显示，CamClient则是一个大统一，把Camera的操作都归集于此。CamClient又把自己的功能分成几个 Client去负责，其中PreviewClient负责显示，RecordClient负责录制，在拍照的功能里FDClient，OTClient，PreviewClient都参了一脚，具体有什么用，有空再研究。但还有一个CameraAdapter，这也非常重要的

    原文作者：Android源码分析
    原文地址: https://blog.csdn.net/shell812/article/details/49425763
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