Surface在C++层的创建源码解析

时间：2021-07-01 18:58:16

Surface在C++层的创建源码解析

源码为：android4.4.4

1、创建SurfaceComposerClient绘图客户端

// create a client to surfaceflinger

sp<SurfaceComposerClient> client = new SurfaceComposerClient();  //创建SurfaceFlinger的本地代理

展开SurfaceComposerClient源码：frameworks\native\libs\gui\SurfaceComposerClient.cpp

SurfaceComposerClient::SurfaceComposerClient()

: mStatus(NO_INIT), mComposer(Composer::getInstance())

// Composer::getInstance() 应该是一个单例模式

{

}

mStatus： 为status_t类型变量  ， mComposer：为Composer&的引用

Composer类为SurfaceComposerClient类的友元类。

Composer::getInstance()获取一个Composer对象赋值给mComposer。

现在client对象的两个变量mStatus和mComposer都有值了。

2、通过client对象获取屏幕信息

DisplayInfo display;

//获取屏幕的宽高等信息

client->getDisplayInfo(client->getBuiltInDisplay(HWC_DISPLAY_PRIMARY), &display);

将获取到的屏幕信息存放发哦display这个结构体里。

看看client->getBuiltInDisplay(HWC_DISPLAY_PRIMARY)这个是什么意思。

sp<IBinder> SurfaceComposerClient::getBuiltInDisplay(int32_t id) {

return Composer::getInstance().getBuiltInDisplay(id);

} //调用Composer的getBuiltInDisplay方法

sp<IBinder> Composer::getBuiltInDisplay(int32_t id) {

return ComposerService::getComposerService()->getBuiltInDisplay(id);

}//再次调用ComposerService对象的getBuiltInDisplay方法

client-> getBuiltInDisplay最终获取到一个Ibinder对象

再看看client->getDisplayInfo这个方法

status_t SurfaceComposerClient::getDisplayInfo(

const sp<IBinder>& display, DisplayInfo* info)

{

return ComposerService::getComposerService()->getDisplayInfo(display, info);

}

根据HWC_DISPLAY_PRIMARY获取Ibinder对象，根据Binder对象获取ComposerSeveice对象调用取得屏幕信息。

3、根据SurfaceComposerClient对象创建SurfafeControl对象

//创建SurfaceControl的本地代理

sp<SurfaceControl> surfaceControl = client->createSurface(String8("testsurface"), display.w, display.h, PIXEL_FORMAT_RGBA_8888, 0);

看看createSurface源码

sp<SurfaceControl> SurfaceComposerClient::createSurface(

const String8& name,

uint32_t w,

uint32_t h,

PixelFormat format,

uint32_t flags)

{

sp<SurfaceControl> sur;

if (mStatus == NO_ERROR) {

sp<IBinder> handle;

sp<IGraphicBufferProducer> gbp;

status_t err = mClient->createSurface(name, w, h, format, flags,

&handle, &gbp); //通知服务端申请surface

ALOGE_IF(err, "SurfaceComposerClient::createSurface error %s", strerror(-err));

if (err == NO_ERROR) {

sur = new SurfaceControl(this, handle, gbp); //如果申请成功就创建

}

}

return sur;

}

mClient是什么东西：sp<ISurfaceComposerClient>  mClient; IsurfaceComposerClient是Binder的一个接口类。

先申请surface申请成功就创建一个surfaceControl的本地代理。

4、设置surface的图层Z轴

SurfaceComposerClient::openGlobalTransaction();

surfaceControl->setLayer(120000); //设置z轴

surfaceControl->setSize(display.w, display.h);

surfaceControl->setPosition(0, 0);  //起始位置

SurfaceComposerClient::closeGlobalTransaction(); //默认false

SurfaceComposerClient::openGlobalTransaction() 源码展开后：

void SurfaceComposerClient::openGlobalTransaction() {

Composer::openGlobalTransaction();

}

static void openGlobalTransaction() {

Composer::getInstance().openGlobalTransactionImpl();

}

void Composer::openGlobalTransactionImpl() {

{ // scope for the lock

Mutex::Autolock _l(mLock);

mTransactionNestCount += 1;  //最终是给这个变量加1

}

}

看看surfaceControl->setLayer(120000)设置z轴展开：

status_t SurfaceComposerClient::setLayer(const sp<IBinder>& id, int32_t z) {

return getComposer().setLayer(this, id, z);

}

status_t Composer::setLayer(const sp<SurfaceComposerClient>& client,

const sp<IBinder>& id, int32_t z) {

Mutex::Autolock _l(mLock);

layer_state_t* s = getLayerStateLocked(client, id);//状态加锁

if (!s)

return BAD_INDEX;

s->what |= layer_state_t::eLayerChanged;

s->z = z;

return NO_ERROR;

}

layer_state_t* Composer::getLayerStateLocked(

const sp<SurfaceComposerClient>& client, const sp<IBinder>& id) {

ComposerState s;

s.client = client->mClient;

s.state.surface = id; //将设置的Z轴坐标存在ComposerState对象里

ssize_t index = mComposerStates.indexOf(s); //查看链表中是否有该坐标

if (index < 0) { //没有就添加

// we don't have it, add an initialized layer_state to our list

index = mComposerStates.add(s); //将这个ComposerState对象存放到链表中

}

ComposerState* const out = mComposerStates.editArray();

return &(out[index].state);

}

以上就是设置Z轴方法，调用Composer对象getLayerStateLocked进行加锁，创建一个ComposerState对象，将传递进来的值存进行检查，检查是否存在，如果不存在就直接储到mComposerStates链表中。

SurfaceComposerClient::closeGlobalTransaction()展开：

void SurfaceComposerClient::closeGlobalTransaction(bool synchronous) {

Composer::closeGlobalTransaction(synchronous);

}

static void closeGlobalTransaction(bool synchronous) {

Composer::getInstance().closeGlobalTransactionImpl(synchronous);

}

void Composer::closeGlobalTransactionImpl(bool synchronous) {

sp<ISurfaceComposer> sm(ComposerService::getComposerService());

Vector<ComposerState> transaction;

Vector<DisplayState> displayTransaction;

uint32_t flags = 0;

{ // scope for the lock

Mutex::Autolock _l(mLock);

mForceSynchronous |= synchronous;

if (!mTransactionNestCount) {

ALOGW("At least one call to closeGlobalTransaction() was not matched by a prior "

"call to openGlobalTransaction().");

} else if (--mTransactionNestCount) { //和锁定时正好相反

return; 直接退出

}

//后面是没有进行上面的锁定，才执行下面该部分

transaction = mComposerStates;

mComposerStates.clear();

displayTransaction = mDisplayStates;

mDisplayStates.clear();

if (mForceSynchronous) {

flags |= ISurfaceComposer::eSynchronous;

}

if (mAnimation) {

flags |= ISurfaceComposer::eAnimation;

}

mForceSynchronous = false;

mAnimation = false;

}

sm->setTransactionState(transaction, displayTransaction, flags);

}

5、获取surface

// 获取Surface本地代理

sp<Surface> surface = surfaceControl->getSurface();//获取surface

sp<Surface> SurfaceControl::getSurface() const

{

Mutex::Autolock _l(mLock);

if (mSurfaceData == 0) {

// This surface is always consumed by SurfaceFlinger, so the

// producerControlledByApp value doesn't matter; using false.

mSurfaceData = new Surface(mGraphicBufferProducer, false);

}

return mSurfaceData;

}

直接new一个suface对象返回

6、surface->lock() 和surface->unlockAndPost();

Lock从屏幕缓冲队列中申请屏幕，再使用unlockAndpost将申请的屏幕加入到缓冲队列中交给surfaceflinger进行组合并显示在屏幕上。其实这才是绘图显示最重要的阶段，绘图显示快慢和这里优化有直接关系。

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