Android6.0 显示系统（二） SurfaceFlinger创建Surface

接上篇博客分析到SurfaceComposerClient中调用createSurface函数会最后调用到SurfaceFlinger的Client的createSurface函数。

我们来看下这个函数，其handle和gbp都是Binder对象，gbp就是图像缓冲区对象。这个handle对象的作用和前面介绍Activity中的token作用类似，也是利用Binder的唯一性为Surface生成一个唯一标识。

status_t Client::createSurface(
const String8& name,
uint32_t w, uint32_t h, PixelFormat format, uint32_t flags,
sp<IBinder>* handle,
sp<IGraphicBufferProducer>* gbp)
{
/*
* createSurface must be called from the GL thread so that it can
* have access to the GL context.
*/

class MessageCreateLayer : public MessageBase {
SurfaceFlinger* flinger;
Client* client;
sp<IBinder>* handle;
sp<IGraphicBufferProducer>* gbp;
status_t result;
const String8& name;
uint32_t w, h;
PixelFormat format;
uint32_t flags;
public:
MessageCreateLayer(SurfaceFlinger* flinger,
const String8& name, Client* client,
uint32_t w, uint32_t h, PixelFormat format, uint32_t flags,
sp<IBinder>* handle,
sp<IGraphicBufferProducer>* gbp)
: flinger(flinger), client(client),
handle(handle), gbp(gbp),
name(name), w(w), h(h), format(format), flags(flags) {
}
status_t getResult() const { return result; }
virtual bool handler() {
result = flinger->createLayer(name, client, w, h, format, flags,
handle, gbp);
return true;
}
};

sp<MessageBase> msg = new MessageCreateLayer(mFlinger.get(),
name, this, w, h, format, flags, handle, gbp);
mFlinger->postMessageSync(msg);
return static_cast<MessageCreateLayer*>( msg.get() )->getResult();
}

这个函数中定义了一个消息类MessageCreateLayer，然后把它的对象通过postMessageSync方法发送出去，这个消息是以同步的方式发送，因此函数结束后可以直接返回结果。因此就直接到了handler函数，在这个函数中调用了SurfaceFlinger的createLayer函数。

一、创建Layer

这个函数会根据传进来的flags来创建普通的的Layer还是模糊的Layer。

status_t SurfaceFlinger::createLayer(
const String8& name,
const sp<Client>& client,
uint32_t w, uint32_t h, PixelFormat format, uint32_t flags,
sp<IBinder>* handle, sp<IGraphicBufferProducer>* gbp)
{
if (int32_t(w|h) < 0) {
ALOGE("createLayer() failed, w or h is negative (w=%d, h=%d)",
int(w), int(h));
return BAD_VALUE;
}

status_t result = NO_ERROR;

sp<Layer> layer;

switch (flags & ISurfaceComposerClient::eFXSurfaceMask) {
case ISurfaceComposerClient::eFXSurfaceNormal:
result = createNormalLayer(client,//普通的
name, w, h, flags, format,
handle, gbp, &layer);
break;
case ISurfaceComposerClient::eFXSurfaceDim://模糊的
result = createDimLayer(client,
name, w, h, flags,
handle, gbp, &layer);
break;
default:
result = BAD_VALUE;
break;
}

if (result != NO_ERROR) {
return result;
}

result = addClientLayer(client, *handle, *gbp, layer);
if (result != NO_ERROR) {
return result;
}

setTransactionFlags(eTransactionNeeded);
return result;
}我们先来看看创建普通的Layer，根据传入的format参数，选择不同格式。然后创建一个Layer，具体Layer我们后续介绍。然后获取handle和gbp。

status_t SurfaceFlinger::createNormalLayer(const sp<Client>& client,
const String8& name, uint32_t w, uint32_t h, uint32_t flags, PixelFormat& format,
sp<IBinder>* handle, sp<IGraphicBufferProducer>* gbp, sp<Layer>* outLayer)
{
// initialize the surfaces
switch (format) {
case PIXEL_FORMAT_TRANSPARENT:
case PIXEL_FORMAT_TRANSLUCENT:
format = PIXEL_FORMAT_RGBA_8888;//透明
break;
case PIXEL_FORMAT_OPAQUE:
format = PIXEL_FORMAT_RGBX_8888;//不透明
break;
}

*outLayer = new Layer(this, client, name, w, h, flags);//创建一个Layer
status_t err = (*outLayer)->setBuffers(w, h, format, flags);
if (err == NO_ERROR) {
*handle = (*outLayer)->getHandle();
*gbp = (*outLayer)->getProducer();
}

ALOGE_IF(err, "createNormalLayer() failed (%s)", strerror(-err));
return err;
}下面我们再来看看模糊的Layer，这个比较简单，直接新建一个layerDim,然后获取handle和gbp。

status_t SurfaceFlinger::createDimLayer(const sp<Client>& client,
const String8& name, uint32_t w, uint32_t h, uint32_t flags,
sp<IBinder>* handle, sp<IGraphicBufferProducer>* gbp, sp<Layer>* outLayer)
{
*outLayer = new LayerDim(this, client, name, w, h, flags);
*handle = (*outLayer)->getHandle();
*gbp = (*outLayer)->getProducer();
return NO_ERROR;
}

二、获取handle

下面我们再来看handle的获取，只是新建一个Handle，而这个Handle只是一个Binder的实现，就是标识Surface的全局唯一性，没有什么实际的内容。

sp<IBinder> Layer::getHandle() {
Mutex::Autolock _l(mLock);

LOG_ALWAYS_FATAL_IF(mHasSurface,
"Layer::getHandle() has already been called");

mHasSurface = true;

/*
* The layer handle is just a BBinder object passed to the client
* (remote process) -- we don't keep any reference on our side such that
* the dtor is called when the remote side let go of its reference.
*
* LayerCleaner ensures that mFlinger->onLayerDestroyed() is called for
* this layer when the handle is destroyed.
*/

class Handle : public BBinder, public LayerCleaner {
wp<const Layer> mOwner;
public:
Handle(const sp<SurfaceFlinger>& flinger, const sp<Layer>& layer)
: LayerCleaner(flinger, layer), mOwner(layer) {
}
};

return new Handle(mFlinger, this);
}

三、gbp图像缓冲区

那么我们再来看看gbp的获取,就是Layer中mProducer成员变量。

sp<IGraphicBufferProducer> Layer::getProducer() const {
return mProducer;
}

而mProducer是在Layer的onFirstRef中赋值的，我们注意MonitoredProducer构造函数的一个参数producer，事实上MonitoredProducer只是一个代理类，真正的实现在这个producer参数。它是在BufferQueue::createBufferQueue中创造的。

void Layer::onFirstRef() {
// Creates a custom BufferQueue for SurfaceFlingerConsumer to use
sp<IGraphicBufferProducer> producer;
sp<IGraphicBufferConsumer> consumer;
BufferQueue::createBufferQueue(&producer, &consumer);
mProducer = new MonitoredProducer(producer, mFlinger);
......

这个producer就是BufferQueueProducer对象。

void BufferQueue::createBufferQueue(sp<IGraphicBufferProducer>* outProducer,
sp<IGraphicBufferConsumer>* outConsumer,
const sp<IGraphicBufferAlloc>& allocator) {

sp<BufferQueueCore> core(new BufferQueueCore(allocator));
sp<IGraphicBufferProducer> producer(new BufferQueueProducer(core));
sp<IGraphicBufferConsumer> consumer(new BufferQueueConsumer(core));

*outProducer = producer;
*outConsumer = consumer;
}下篇博客我们就分析这个。