Android 5.0 Camera系统源码分析(4)：Camera预览流程数据流

最新推荐文章于 2022-11-23 19:24:49 发布

陈纪建

最新推荐文章于 2022-11-23 19:24:49 发布

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CC 4.0 BY-SA版权

分类专栏： Android 拍照源码分析

本文链接：https://blog.youkuaiyun.com/u013898698/article/details/76572188

上一篇讲了怎么让Camera进入预览模式，提到了DisplayClient负责显示图像数据，而CamAdapter负责提供图像数据，这里主要记录了CamAdapter怎么获取图像，然后DisplayClient怎么将图像显示在屏幕上。

2. DisplayClient

上一篇提到在setPreviewWindow的时候会构造并初始化DisplayClient，之前没有仔细分析，现在来看看

bool 
DisplayClient:: 
init() 
{ 
    bool ret = false; 

    ret =   createDisplayThread() 
        &&  createImgBufQueue();

    return  ret; 
} 
 
 
  
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创建了一个显示线程和一个ImgBuf队列，看下这两个函数的具体实现

bool 
DisplayClient:: 
createDisplayThread() 
{ 
    bool    ret = false; 
    status_t status = OK; 

    mpDisplayThread = IDisplayThread::createInstance(this); 
    if  ( mpDisplayThread == 0 ||  OK != (status = mpDisplayThread->run()) ) 
    { 
        ......
    } 

    ret = true; 
lbExit: 
    return  ret; 
} 
 
 
  
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bool 
DisplayClient:: 
createImgBufQueue() 
{ 
    bool ret = false; 

    mpImgBufQueue = new ImgBufQueue(IImgBufProvider::eID_DISPLAY, "CameraDisplay@ImgBufQue"); 
    if  ( mpImgBufQueue == 0 ) 
    { 
        MY_LOGE("Fail to new ImgBufQueue"); 
        goto lbExit; 
    }
    ......
    ret = true; 
lbExit: 
    MY_LOGD("-"); 
    return  ret; 
}
 
 
  
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ImgBufQueue暂时放一边，createDisplayThread创建了DisplayThread，作为线程关注的重点当然是threadLoop，所以接着看DisplayThread的threadLoop函数

bool
DisplayThread::
threadLoop()
{
    Command cmd;
    if  ( getCommand(cmd) )
    {   
        switch  (cmd.eId)
        {   
        case Command::eID_EXIT:
            MY_LOGD("Command::%s", cmd.name());
            break;

        case Command::eID_WAKEUP:
        default:
            if  ( mpThreadHandler != 0 ) 
            {   
                mpThreadHandler->onThreadLoop(cmd);
            }
            break;
        }   
    }   

    return  true;
}
 
 
  
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DisplayThread将接收WAKEUP命令，然后做出响应。那么由谁来发这个WAKEUP命令呢，就在上一篇提到的enableDisplayClient函数里面发送。这里的mpThreadHandler 指的是DisplayClient，也就是在接收到WAKEUP命令后，将回调DisplayClient的onThreadLoop函数

bool
DisplayClient::
onThreadLoop(Command const& rCmd)
{
    //  (0) lock Processor.
    sp<IImgBufQueue> pImgBufQueue;
    {
        Mutex::Autolock _l(mModuleMtx);
        pImgBufQueue = mpImgBufQueue;
        if  ( pImgBufQueue == 0 || ! isDisplayEnabled() )
        {
            MY_LOGW("pImgBufQueue.get(%p), isDisplayEnabled(%d)", pImgBufQueue.get(), isDisplayEnabled());
            return  true;
        }
    }

    //  (1) Prepare all TODO buffers.
    if  ( ! prepareAllTodoBuffers(pImgBufQueue) )
    {
        return  true;
    }

    //  (2) Start
    if  ( ! pImgBufQueue->startProcessor() )
    {
        return  true;
    }

    //  (3) Do until disabled.
    while(1)
    {
        //  (.1)
        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.
        prepareAllTodoBuffers(pImgBufQueue);
    }

    ......

    return  true;
}
 
 
  
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先分析步骤(1)准备好接收数据的buffers

/******************************************************************************
*   dequePrvOps() -> enqueProcessor() & enque Buf List
*******************************************************************************/
bool
DisplayClient::
prepareAllTodoBuffers(sp<IImgBufQueue>const& rpBufQueue)
{       
    bool ret = false;

    while   ( mStreamBufList.size() < (size_t)mi4MaxImgBufCount )
    {   
        if  ( ! prepareOneTodoBuffer(rpBufQueue) )
        {
   
   
            break;
        }
    }   

    return ret;
}
 
 
  
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bool
DisplayClient::
prepareOneTodoBuffer(sp<IImgBufQueue>const& rpBufQueue)
{
    bool ret = false;

    ......

    //  (2) deque it from PrvOps
    sp<StreamImgBuf> pStreamImgBuf;
    if  ( ! dequePrvOps(pStreamImgBuf) )
    {   
        goto lbExit;
    }   

    //  (3) enque it into Processor
    ret = rpBufQueue->enqueProcessor(
        ImgBufQueNode(pStreamImgBuf, ImgBufQueNode::eSTATUS_TODO)
    );

    //  (4) enque it into List & increment the list size.
    mStreamBufList.push_back(pStreamImgBuf);

    ret = true;
lbExit:
    MY_LOGD_IF((2<=miLogLevel), "- ret(%d)", ret);
    return ret;
}
 
 
  
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