surface的创建过程

最新推荐文章于 2024-08-01 17:16:11 发布

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最新推荐文章于 2024-08-01 17:16:11 发布 · 1.8k 阅读

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本文详细剖析了Android中Surface的创建过程，从ViewRootImpl的mSurface开始，经过SurfaceSession的创建，到SurfaceComposerClient、SurfaceControl的生成，最终完成Surface的初始化。涉及关键步骤包括SurfaceSession的JNI创建、SurfaceFlinger的交互以及WindowSurfaceController的构造。

还是首先来看一个序列图：
在这里插入图片描述

1.ViewRootImpl.mSurface

ViewRootImpl这个类是是处理视图绘画，input输入，调用wms调用窗口的核心类。其成员变量mSurface在申明的时候就初始化了：

    final Surface mSurface = new Surface();

上面干巴巴的创建了Surface实例，进去看Surface这个类的无参构造函数也是个空的，所以还要继续往下分析

2.SurfaceSession的创建

在wms窗口管理过程中，视图的添加过程
ViewRootImpl.setView-> session.addToDisplay->WMS.addWindow
在WMS中添加窗口WindowState完成后，会调用WindowState类的attach函数
在这里插入图片描述

    void attach() {
   
   
        if (localLOGV) Slog.v(TAG, "Attaching " + this + " token=" + mToken);
        mSession.windowAddedLocked(mAttrs.packageName);
    }
    void windowAddedLocked(String packageName) {
   
   
        mPackageName = packageName;
        mRelayoutTag = "relayoutWindow: " + mPackageName;
        if (mSurfaceSession == null) {
   
   
            if (WindowManagerService.localLOGV) Slog.v(
                TAG_WM, "First window added to " + this + ", creating SurfaceSession");
            mSurfaceSession = new SurfaceSession();
            if (SHOW_TRANSACTIONS) Slog.i(
                    TAG_WM, "  NEW SURFACE SESSION " + mSurfaceSession);
            mService.mSessions.add(this);
            if (mLastReportedAnimatorScale != mService.getCurrentAnimatorScale()) {
   
   
                mService.dispatchNewAnimatorScaleLocked(this);
            }
        }
        mNumWindow++;
    }

上面就可以看到session的成员变量mSurfaceSession的赋值操作，这里通过
new SurfaceSession()创建了一个实例，下面我们看看SurfaceSession的构造函数。

3.SurfaceSession

    private long mNativeClient; // SurfaceComposerClient*

    public SurfaceSession() {
   
   
        mNativeClient = nativeCreate();
    }

    public SurfaceSession(Surface root) {
   
   
        mNativeClient = nativeCreateScoped(root.mNativeObject);
    }

这里就是获取SurfaceComposerClient的指针地址，而其实现方式是通过JNI来的，这里我们来看看其JNI的实现

4android_view_SurfaceSession.nativeCreate

static jlong nativeCreate(JNIEnv* env, jclass clazz) {
   
   
    SurfaceComposerClient* client = new SurfaceComposerClient();
    client->incStrong((void*)nativeCreate);
    return reinterpret_cast<jlong>(client);
}

上面的代码就是new了一个SurfaceComposerClient对象，然后返回了这个对象的地址，也就是我们实际得到的是SurfaceComposerClient实例

5.SurfaceComposerClient

SurfaceComposerClient::SurfaceComposerClient()
    : mStatus(NO_INIT), mComposer(Composer::getInstance())
{
   
   
}

SurfaceComposerClient::SurfaceComposerClient(const sp<IGraphicBufferProducer>& root)
    : mStatus(NO_INIT), mComposer(Composer::getInstance()), mParent(root)
{
   
   
}

void SurfaceComposerClient::onFirstRef() {
   
   
    sp<ISurfaceComposer> sm(ComposerService::getComposerService());
    if (sm != 0) {
   
   
        auto rootProducer = mParent.promote();
        sp<ISurfaceComposerClient> conn;
        conn = (rootProducer != nullptr) ? sm->createScopedConnection(rootProducer) :
                sm->createConnection();
        if (conn != 0) {
   
   
            mClient = conn;
            mStatus = NO_ERROR;
        }
    }
}
void ComposerService::connectLocked() {
   
   
    const String16 name("SurfaceFlinger");
    while (getService(name, &mComposerService) != NO_ERROR) {
   
   
        usleep(250000);
    }
    assert(mComposerService != NULL);

    // Create the death listener.
    class DeathObserver : public IBinder::DeathRecipient {
   
   
        ComposerService& mComposerService;
        virtual void binderDied(const wp<IBinder>& who) {
   
   
            ALOGW("ComposerService remote (surfaceflinger) died [%p]",
                  who.unsafe_get());
            mComposerService.composerServiceDied();
        }
     public:
        explicit DeathObserver(ComposerService& mgr) : mComposerService(mgr) {
   
    }
    };

    mDeathObserver = new DeathObserver(*const_cast<ComposerService*>(this));
    IInterface::asBinder(mComposerService)->linkToDeath(mDeathObserver);
}

1.在onFirstRef函数里面会获取fingerprint的服务，看connectLocked实现就可以确定，通过getservice这个API获取指定的SurfaceFlinger服务实例，这样一来client就和surfaceflinger建立了联系。
2.当获取了Surfaceflinger实例后，调用createScopedConnection来创建client

6.createScopedConnection

sp<ISurfaceComposerClient> SurfaceFlinger::createScopedConnection

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