Android 5.0 Camera系统源码分析(5)：
Camera预览3A流程
1. 前言
本文分析的是Android Hal层的源码，硬件平台基于mt6735。之前几篇讲的预览流程中3A相关的环节都忽略了，现在重新整理下。
3A指的是Auto Exposure，Auto Focus，Auto White Balance。这三个一起放上来代码实在太多了，这里将重点记录AF的代码。AF的部分工作是由ISP完成的，而ISP的大部分代码mtk都没有开放给我们，比如ISP是如何计算得到对焦位置信息的，但得到对焦位置之后怎么操作对焦马达的代码我们是看得到的，所以涉及到ISP的一些代码将被略过
2. 初始化3A
3A的初始化在DefaultCam1Device的onInit函数里面开始，之前在camera打开流程里面已经提到过 bool
DefaultCam1Device:: onInit() {
......
// (1) Open 3A
mpHal3a = NS3A::IHal3A::createInstance( NS3A::IHal3A::E_Camera_1, getOpenId(), LOG_TAG); ...... }
构造一个Hal3A对象，看下Hal3A::createInstance的实现
Hal3A* Hal3A::
createInstance(MINT32 i4SensorDevId, MINT32 i4SensorOpenIndex) {
switch (i4SensorDevId) {
case SENSOR_DEV_MAIN:
Hal3ADev
return Hal3ADev
break;
case SENSOR_DEV_SUB:
Hal3ADev
return Hal3ADev
其实这里的Hal3A并没有直接继承IHal3A，也就是说从IHal3A::createInstance到Hal3A::createInstance的调用过程经历了一番波折，但暂时不用关心它。从Hal3A::createInstance可以看到除了实例化以外还会调用init函数。构造函数没什么好看的-略过，直接看init函数
MRESULT Hal3A::
init(MINT32 i4SensorDevId, MINT32 i4SensorOpenIndex) {
...... // (1)
mpStateMgr = new StateMgr(i4SensorDevId); // (2)
bRet = postCommand(ECmd_Init); // (3)
createThread(); // (4)
bRet = IspTuningMgr::getInstance().init(m_i4SensorDev, m_i4SensorOpenIdx); // (5)
ret = EnableAFThread(1); ......
return S_3A_OK; }
步骤(1) new StateMgr，构造函数如下
StateMgr::StateMgr(MINT32 sensorDevId) : ...... {
#define STATE_INITIALIZE(_state_)\\
mpIState[eState_##_state_] = new State##_state_(sensorDevId, this);
STATE_INITIALIZE(Init);
STATE_INITIALIZE(Uninit);
STATE_INITIALIZE(CameraPreview); STATE_INITIALIZE(CamcorderPreview); STATE_INITIALIZE(Recording); STATE_INITIALIZE(Precapture); STATE_INITIALIZE(Capture); STATE_INITIALIZE(AF);
mpCurrentState = mpIState[eState_Uninit]; }
初始化3A的状态管理，将各个子状态都保存在mpIState数组里面，并将当前状态设置为Uninit状态
步骤(2) postCommand
MBOOL Hal3A::postCommand(ECmd_T const eCmd, MINTPTR const i4Arg) {
......
ERROR_CHECK(mpStateMgr->sendCmd(eCmd)) ...... }
MRESULT StateMgr::sendCmd(ECmd_T eCmd) {
Mutex::Autolock lock(m_Lock);
EIntent_T eNewIntent = static_cast
#define SEND_INTENT(_intent_)\\
case _intent_: return mpCurrentState->sendIntent(intent2type<_intent_>());\\
switch (eNewIntent) {
SEND_INTENT(eIntent_CameraPreviewStart) SEND_INTENT(eIntent_CameraPreviewEnd) SEND_INTENT(eIntent_CaptureStart) SEND_INTENT(eIntent_CaptureEnd) SEND_INTENT(eIntent_RecordingStart) SEND_INTENT(eIntent_RecordingEnd) SEND_INTENT(eIntent_AFUpdate) SEND_INTENT(eIntent_AFStart) SEND_INTENT(eIntent_AFEnd) SEND_INTENT(eIntent_Init)
SEND_INTENT(eIntent_Uninit) }
return -1; }
从步骤(1)可以看出这里的mpCurrentState指向的是StateUninit对象，所以接着看StateUninit的sendIntent函数
MRESULT StateUninit::
sendIntent(intent2type
MY_LOG(\
// AAO DMA buffer init
MINT32 i4SensorIdx = m_pHal3A->getSensorOpenIdx();
if (ENABLE_3A_GENERAL & m_pHal3A->m_3ACtrlEnable) { if (ENABLE_AAOBUF & m_pHal3A->m_3ACtrlEnable) { // AAO DMA buffer init
if (!IAAOBufMgr::getInstance().init(m_SensorDevId, i4SensorIdx)) { MY_ERR(\ return E_3A_ERR; }
if (!IAEBufMgr::getInstance().init(m_SensorDevId, i4SensorIdx)) { MY_ERR(\ return E_3A_ERR; } }
if (ENABLE_AFOBUF & m_pHal3A->m_3ACtrlEnable) { // AFO DMA buffer init
if (!IAFOBufMgr::getInstance().init(m_SensorDevId, i4SensorIdx)) { MY_ERR(\ return E_3A_ERR; } } }
// State transition: eState_Uninit --> eState_Init
m_pStateMgr->transitState(eState_Uninit, eState_Init);
return S_3A_OK; }
做了一堆乱七八糟的初始化之后将3A状态从Uninit状态切换到Init状态
步骤(3) createThread和步骤(5) EnableAFThread
MVOID
Hal3A::createThread() {
......
pthread_create(&mThread, NULL, onThreadLoop, this); pthread_create(&mPDThread, NULL, PDThreadLoop, this);
pthread_create(&mPDVCThread, NULL, PDVCThreadLoop, this); ...... }
MRESULT Hal3A::EnableAFThread(MINT32 a_bEnable) {
if (a_bEnable) {
if (mbAFThreadLoop== 0) {
......
pthread_create(&mAFThread, &attr, AFThreadFunc, this); } } else { ...... }
return ret; }
一共创建了4个线程，暂时只关心onThreadLoop 和AFThreadFunc。onThreadLoop是3A主线程，负责接收处理命令；AFThreadFunc负责实时更新AF参数