Android(安卓)SurfaceFlinger学习文档

参考资料：
1、“Android Display System --- Surface Flinger”
2、“Android核心分析(26) ----- Android GDI之SurfaceFlinger”
3、“Android SurfaceFlinger中的SharedClient -- 客户端（Surface）和服务端（Layer）之间的显示缓冲区管理”
4、“Android SurfaceFlinger中的工作线程：threadLoop()”

一、 surfaceflinger server如何启动：

1、【System_init.cpp】

extern "C" status_t system_init()

{

……..

char propBuf[PROPERTY_VALUE_MAX];

property_get("system_init.startsurfaceflinger", propBuf, "1");

if (strcmp(propBuf, "1") == 0) {

// Start the SurfaceFlinger

SurfaceFlinger::instantiate(); //实例化

}

……..

}

2、【SurfaceFlinger.cpp】

void SurfaceFlinger::instantiate() {

defaultServiceManager()->addService(

String16("SurfaceFlinger"), new SurfaceFlinger()); //添加SurfaceFlinger服务

}

3、【Threads.cpp】

int Thread::_threadLoop(void* user)

{

……..

self->mStatus = self->readyToRun();

……..

result = self->threadLoop();

……..

4、【SurfaceFlinger.cpp】

status_t SurfaceFlinger::readyToRun()

{

……..

}

5、【SurfaceFlinger.cpp】

bool SurfaceFlinger::threadLoop()

{

……..

}

二、上层如何与底层SurfaceFlinger建立联系

1、为应用程序创建一个 Client (用于管理和通信)

【SurfaceComposerClient.cpp】
SurfaceComposerClient::SurfaceComposerClient()
{
sp<ISurfaceComposer> sm(getComposerService());
if (sm == 0) {
_init(0, 0);
return;
}

_init(sm, sm->createConnection());

if (mClient != 0) {
Mutex::Autolock _l(gLock);
VERBOSE("Adding client %p to map", this);
gActiveConnections.add(mClient->asBinder(), this);
}
}

注：

经过Binder，最终调用SurfaceFlinger的createConnection实现，这里不作详细介绍，有兴趣请看参考：

“Android 核心分析之六 -----IPC框架分析 Binder，Service，Service manager”
http://blog.csdn.net/maxleng/article/details/5490770

【SurfaceFlinger.cpp】

sp<ISurfaceFlingerClient> SurfaceFlinger::createConnection()

{

Mutex::Autolock _l(mStateLock);

uint32_t token = mTokens.acquire();

sp<Client> client = new Client(token, this);

if (client->ctrlblk == 0) {

mTokens.release(token);

return 0;

}

status_t err = mClientsMap.add(token, client);

if (err < 0) {

mTokens.release(token);

return 0;

}

sp<BClient> bclient =

new BClient(this, token, client->getControlBlockMemory());

return bclient;

}

2、为这个 Client 分配 Surface（用于存放数据）

【SurfaceComposerClient.cpp】 sp<SurfaceControl> SurfaceComposerClient::createSurface(
int pid,
const String8& name,
DisplayID display,
uint32_t w,
uint32_t h,
PixelFormat format,
uint32_t flags)
{
sp<SurfaceControl> result;
if (mStatus == NO_ERROR) {
ISurfaceFlingerClient::surface_data_t data;
sp<ISurface> surface = mClient->createSurface(&data, pid, name,
display, w, h, format, flags);
if (surface != 0) {
if (uint32_t(data.token) < NUM_LAYERS_MAX) {
result = new SurfaceControl(this, surface, data, w, h, format, flags);
}
}
}
return result;
}

【SurfaceFlinger.cpp】
sp<ISurface> BClient::createSurface(
ISurfaceFlingerClient::surface_data_t* params, int pid,
const String8& name,
DisplayID display, uint32_t w, uint32_t h, PixelFormat format,
uint32_t flags)
{
return mFlinger->createSurface(mId, pid, name, params, display, w, h,
format, flags);
}

sp<ISurface> SurfaceFlinger::createSurface(ClientID clientId, int pid,

const String8& name, ISurfaceFlingerClient::surface_data_t* params,

DisplayID d, uint32_t w, uint32_t h, PixelFormat format,

uint32_t flags)

{

sp<LayerBaseClient> layer;

sp<LayerBaseClient::Surface> surfaceHandle;

if (int32_t(w|h) < 0) {

LOGE("createSurface() failed, w or h is negative (w=%d, h=%d)",

int(w), int(h));

return surfaceHandle;

}

Mutex::Autolock _l(mStateLock);

sp<Client> client = mClientsMap.valueFor(clientId);

if (UNLIKELY(client == 0)) {

LOGE("createSurface() failed, client not found (id=%d)", clientId);

return surfaceHandle;

}

//LOGD("createSurface for pid %d (%d x %d)", pid, w, h);

int32_t id = client->generateId(pid);

if (uint32_t(id) >= NUM_LAYERS_MAX) { //最大支持32个layer

LOGE("createSurface() failed, generateId = %d", id);

return surfaceHandle;

}

switch (flags & eFXSurfaceMask) {

case eFXSurfaceNormal:

if (UNLIKELY(flags & ePushBuffers)) {

layer = createPushBuffersSurfaceLocked(client, d, id,

w, h, flags);

} else {

layer = createNormalSurfaceLocked(client, d, id,

w, h, flags, format);

}

break;

case eFXSurfaceBlur:

layer = createBlurSurfaceLocked(client, d, id, w, h, flags);

break;

case eFXSurfaceDim:

layer = createDimSurfaceLocked(client, d, id, w, h, flags);

break;

}

if (layer != 0) {

layer->setName(name);

setTransactionFlags(eTransactionNeeded);

surfaceHandle = layer->getSurface(); //获取Isurface结构

if (surfaceHandle != 0) { //保存好layer信息

params->token = surfaceHandle->getToken();

params->identity = surfaceHandle->getIdentity();

params->width = w;

params->height = h;

params->format = format;

}

return surfaceHandle;

}

sp<LayerBaseClient> SurfaceFlinger::createNormalSurfaceLocked(

const sp<Client>& client, DisplayID display,

int32_t id, uint32_t w, uint32_t h, uint32_t flags,

PixelFormat& format)

{

// initialize the surfaces

switch (format) { // TODO: take h/w into account

case PIXEL_FORMAT_TRANSPARENT:

case PIXEL_FORMAT_TRANSLUCENT:

format = PIXEL_FORMAT_RGBA_8888;

break;

case PIXEL_FORMAT_OPAQUE:

format = PIXEL_FORMAT_RGB_565;

break;

}

sp<Layer> layer = new Layer(this, display, client, id);

status_t err = layer->setBuffers(w, h, format, flags);

if (LIKELY(err == NO_ERROR)) {

layer->initStates(w, h, flags);

addLayer_l(layer);

} else {

LOGE("createNormalSurfaceLocked() failed (%s)", strerror(-err));

layer.clear();

}

return layer;

}

【Layer.cpp】
Layer::Layer(SurfaceFlinger* flinger, DisplayID display,
const sp<Client>& c, int32_t i)
: LayerBaseClient(flinger, display, c, i),
mSecure(false),
mNoEGLImageForSwBuffers(false),
mNeedsBlending(true),
mNeedsDithering(false)
{
// no OpenGL operation is possible here, since we might not be
// in the OpenGL thread.
mFrontBufferIndex = lcblk->getFrontBuffer();
}

【LayerBase.cpp】
LayerBaseClient::LayerBaseClient(SurfaceFlinger* flinger, DisplayID display,
const sp<Client>& client, int32_t i)
: LayerBase(flinger, display), lcblk(NULL), client(client), mIndex(i),
mIdentity(uint32_t(android_atomic_inc(&sIdentity)))
{
lcblk = new SharedBufferServer(
client->ctrlblk, i, NUM_BUFFERS, //建立双buffer
mIdentity);
}

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