Android 12(S) 图像显示系统 - Surface 一点补充知识（十二）
必读：
Android 12(S) 图像显示系统 - 开篇
一、前言
因为个人工作主要是Android多媒体播放的内容，在工作中查看源码或设计程序经常会遇到调用API：
static inline int native_window_api_connect(struct ANativeWindow* window, int api)
static inline int native_window_api_disconnect(struct ANativeWindow* window, int api)所以也一直好奇这两个方法都做了什么事情？这篇文章就来一探究竟。
二、native_window_api_connect 解析
Android系统中，开始播放视频并设置Surface后，都会做一次 connectToSurface 的操作，比如MediaCodec中，在初始化阶段setSurface后就会调用方法：
status_t MediaCodec::connectToSurface(const sp<Surface> &surface) {
...
err = nativeWindowConnect(surface.get(), "connectToSurface");
...
}这里就是去调用了 /frameworks/av/media/libstagefright/SurfaceUtils.cpp 中的方法：
status_t nativeWindowConnect(ANativeWindow *surface, const char *reason) {
ALOGD("connecting to surface %p, reason %s", surface, reason);
status_t err = native_window_api_connect(surface, NATIVE_WINDOW_API_MEDIA);
ALOGE_IF(err != OK, "Failed to connect to surface %p, err %d", surface, err);
return err;
}是不是看到了 native_window_api_connect ，其中参数 NATIVE_WINDOW_API_MEDIA 表明 video decoder会作为生产者来生成buffer数据。
再接着往下走，看看到底做了什么？
大体的调用流程如下：
/frameworks/native/libs/gui/Surface.cpp
/frameworks/native/libs/gui/BufferQueueProducer.cpp
>>> static inline int native_window_api_connect(struct ANativeWindow* window, int api)
>>> int Surface::hook_perform(ANativeWindow* window, int operation, ...)
>>> int Surface::perform(int operation, va_list args)
>>> int Surface::dispatchConnect(va_list args)
>>> int Surface::connect(int api)
>>> int Surface::connect(int api, const sp<IProducerListener>& listener)
>>> int Surface::connect(int api, const sp<IProducerListener>& listener, bool reportBufferRemoval)
>>> status_t BufferQueueProducer::connect(const sp<IProducerListener>& listener,
int api, bool producerControlledByApp, QueueBufferOutput *output)
最终进入到了BufferQueueProducer::connect函数中，看起来这里应该就是做具体事情的地方了
老规矩，看源码：
status_t BufferQueueProducer::connect(const sp<IProducerListener>& listener,
int api, bool producerControlledByApp, QueueBufferOutput *output) {
ATRACE_CALL();
std::lock_guard<std::mutex> lock(mCore->mMutex);
mConsumerName = mCore->mConsumerName; // 消费者名字
BQ_LOGV("connect: api=%d producerControlledByApp=%s", api,
producerControlledByApp ? "true" : "false");
// 对一些条件进行判断，必要时直接返回return
if (mCore->mIsAbandoned) {
BQ_LOGE("connect: BufferQueue has been abandoned");
return NO_INIT;
}
if (mCore->mConsumerListener == nullptr) {
BQ_LOGE("connect: BufferQueue has no consumer");
return NO_INIT;
}
if (output == nullptr) {
BQ_LOGE("connect: output was NULL");
return BAD_VALUE;
}
if (mCore->mConnectedApi != BufferQueueCore::NO_CONNECTED_API) {
BQ_LOGE("connect: already connected (cur=%d req=%d)",
mCore->mConnectedApi, api);
return BAD_VALUE;
}
int delta = mCore->getMaxBufferCountLocked(mCore->mAsyncMode,
mDequeueTimeout < 0 ?
mCore->mConsumerControlledByApp && producerControlledByApp : false,
mCore->mMaxBufferCount) -
mCore->getMaxBufferCountLocked();
if (!mCore->adjustAvailableSlotsLocked(delta)) {
BQ_LOGE("connect: BufferQueue failed to adjust the number of available "
"slots. Delta = %d", delta);
return BAD_VALUE;
}
int status = NO_ERROR;
switch (api) {
case NATIVE_WINDOW_API_EGL:
case NATIVE_WINDOW_API_CPU:
case NATIVE_WINDOW_API_MEDIA:
case NATIVE_WINDOW_API_CAMERA:
mCore->mConnectedApi = api;
output->width = mCore->mDefaultWidth;
output->height = mCore->mDefaultHeight;
output->transformHint = mCore->mTransformHintInUse = mCore->mTransformHint;
output->numPendingBuffers =
static_cast<uint32_t>(mCore->mQueue.size());
output->nextFrameNumber = mCore->mFrameCounter + 1;
output->bufferReplaced = false;
output->maxBufferCount = mCore->mMaxBufferCount;
if (listener != nullptr) {
// Set up a death notification so that we can disconnect
// automatically if the remote producer dies
#ifndef NO_BINDER
if (IInterface::asBinder(listener)->remoteBinder() != nullptr) {
status = IInterface::asBinder(listener)->linkToDeath(
static_cast<IBinder::DeathRecipient*>(this));
if (status != NO_ERROR) {
BQ_LOGE("connect: linkToDeath failed: %s (%d)",
strerror(-status), status);
}
mCore->mLinkedToDeath = listener;
}
#endif
mCore->mConnectedProducerListener = listener; // 设置producer listener
mCore->mBufferReleasedCbEnabled = listener->needsReleaseNotify();
}
break;
default:
BQ_LOGE("connect: unknown API %d", api);
status = BAD_VALUE;
break;
}
mCore->mConnectedPid = BufferQueueThreadState::getCallingPid();
mCore->mBufferHasBeenQueued = false;
mCore->mDequeueBufferCannotBlock = false;
mCore->mQueueBufferCanDrop = false;
mCore->mLegacyBufferDrop = true;
if (mCore->mConsumerControlledByApp && producerControlledByApp) {
mCore->mDequeueBufferCannotBlock = mDequeueTimeout < 0;
mCore->mQueueBufferCanDrop = mDequeueTimeout <= 0;
}
mCore->mAllowAllocation = true; // 允许分配 graphic buffer
VALIDATE_CONSISTENCY();
return status;
}我才疏学浅，按我理解，就是完成了一些初始化的操作，貌似也没啥了，这之后应该produder就可以 dequeue buffer 了
另外一点，这里有设置producer listener，之前文章中也讲过，貌似也没啥作用(也许我错了)
mCore->mConnectedProducerListener = listener;
mCore->mBufferReleasedCbEnabled = listener->needsReleaseNotify();
三、native_window_api_disconnect 解析
disconnect的调用流程和connect的流程类似。
