SurfaceFlinger原理（一）：SurfaceFlinger的初始化

SurfaceFlinger是Android的一个native进程，负责将图层进行合成，图层叠加起来就构成了我们看到的界面。合成的方式分为在线合成和离线合成。在线合成是指现在一块buffer画好所有的内容，然后直接交给linux图像驱动framebuffer显示出来；离线合成是指将一些图层的buffer直接递交HWComposer，HWComposer指的是能够处理图像数据并组合的现实硬件模块（有些设备上可能没有），当需要显示某一行的数据时，再将这些图层的数据进行处理组合后再交给framebuffer显示出来，合成方式有MDP，DYN，C2D等，反正不是GPU，因而减轻了GPU负担。
SurfaceFlinger启动的main函数在main_surfaceflinger.cpp中。最后的run函数使SurfaceFlinger进程陷入do…while循环中，不会退出。我们重点关注SurfaceFlinger的init函数。

/frameworks/native/services/surfaceflinger/main_surfaceflinger.cppint main(int, char**) {// When SF is launched in its own process, limit the number of// binder threads to 4.ProcessState::self()->setThreadPoolMaxThreadCount(4);// start the thread poolsp<ProcessState> ps(ProcessState::self());ps->startThreadPool();// instantiate surfaceflingersp<SurfaceFlinger> flinger = new SurfaceFlinger();#if defined(HAVE_PTHREADS)setpriority(PRIO_PROCESS, 0, PRIORITY_URGENT_DISPLAY);
#endifset_sched_policy(0, SP_FOREGROUND);// initialize before clients can connectflinger->init();// publish surface flingersp<IServiceManager> sm(defaultServiceManager());sm->addService(String16(SurfaceFlinger::getServiceName()), flinger, false);// run in this threadflinger->run();return 0;
}

下面介绍的情况均以只有一个主屏幕（id为0）为前提，实际上Android支持三种屏幕：主屏幕，外接屏幕（HDMI等），虚拟屏幕（投屏）。init函数的主要工作有：1.初始化EGL的一些环境以及设置；2.启动hwc；3.搜寻可用的屏幕,初始化屏幕的一些信息，新建DisplayDevice和FramebufferSurface，并分别作为生产者和消费者；4.分别为app端和SurfaceFlinger建立一个EventThread以响应vysnc信号；5.启动bootanimation。

/frameworks/native/services/surfaceflinger/SurfaceFlinger.cpp

void SurfaceFlinger::init() {
ALOGI( "SurfaceFlinger's main thread ready to run. "
"Initializing graphics H/W...");

status_t err;
Mutex::Autolock _l(mStateLock);

// initialize EGL for the default display
//初始化EGL环境
mEGLDisplay = eglGetDisplay(EGL_DEFAULT_DISPLAY);
eglInitialize(mEGLDisplay, NULL, NULL);

// Initialize the H/W composer object. There may or may not be an
// actual hardware composer underneath.
//初始化hwc
mHwc = new HWComposer(this,
*static_cast<HWComposer::EventHandler *>(this));

// get a RenderEngine for the given display / config (can't fail)
//创建RenderEngine，RenderEngine封装了一些OpenGL的操作
mRenderEngine = RenderEngine::create(mEGLDisplay, mHwc->getVisualID());

// retrieve the EGL context that was selected/created
//获取EGL上下文
mEGLContext = mRenderEngine->getEGLContext();

LOG_ALWAYS_FATAL_IF(mEGLContext == EGL_NO_CONTEXT,
"couldn't create EGLContext");

// initialize our non-virtual displays
for (size_t i=0 ; i<DisplayDevice::NUM_BUILTIN_DISPLAY_TYPES ; i++) {
DisplayDevice::DisplayType type((DisplayDevice::DisplayType)i);
// set-up the displays that are already connected
//屏幕可用或者为主屏幕
if (mHwc->isConnected(i) || type==DisplayDevice::DISPLAY_PRIMARY) {
// All non-virtual displays are currently considered secure.
bool isSecure = true;
//创建内置屏幕，每个屏幕id对应一个binder对象
createBuiltinDisplayLocked(type);
wp<IBinder> token = mBuiltinDisplays[i];

//创建生产者和消费者
sp<IGraphicBufferProducer> producer;
sp<IGraphicBufferConsumer> consumer;
BufferQueue::createBufferQueue(&producer, &consumer,
new GraphicBufferAlloc());
//新建FramebufferSurface作为消费者，向framebuffer传递数据就靠它了
sp<FramebufferSurface> fbs = new FramebufferSurface(*mHwc, i,
consumer);
//为屏幕创建hwc层的id
int32_t hwcId = allocateHwcDisplayId(type);
//新建DisplayDevice生产者，与显示画面有关
sp<DisplayDevice> hw = new DisplayDevice(this,
type, hwcId, mHwc->getFormat(hwcId), isSecure, token,
fbs, producer,
mRenderEngine->getEGLConfig());
if (i > DisplayDevice::DISPLAY_PRIMARY) {
// FIXME: currently we don't get blank/unblank requests
// for displays other than the main display, so we always
// assume a connected display is unblanked.
ALOGD("marking display %zu as acquired/unblanked", i);
hw->setPowerMode(HWC_POWER_MODE_NORMAL);
}
//屏幕id的对应的binder对象和DisplayDevice组成键值对，保存在mDisplays
mDisplays.add(token, hw);
}
}

// make the GLContext current so that we can create textures when creating Layers
// (which may happens before we render something)
//DisplayDevice::makeCurrent会调用到eglMakeCurrent，libagl.so的实现里eglMakeCurrent会dequeue一块buffer
getDefaultDisplayDevice()->makeCurrent(mEGLDisplay, mEGLContext);

// start the EventThread
//基于不同的vsync信号模型创建的EventThread,mEventThread是app端对vsync信号的处理线程，mSFEventThread是SurfaceFlinger端对vysnc信号的处理线程
sp<VSyncSource> vsyncSrc = new DispSyncSource(&mPrimaryDispSync,
vsyncPhaseOffsetNs, true, "app");
mEventThread = new EventThread(vsyncSrc);
sp<VSyncSource> sfVsyncSrc = new DispSyncSource(&mPrimaryDispSync,
sfVsyncPhaseOffsetNs, true, "sf");
mSFEventThread = new EventThread(sfVsyncSrc);
mEventQueue.setEventThread(mSFEventThread);
//mEventControlThread线程用来开关vsync
mEventControlThread = new EventControlThread(this);
mEventControlThread->run("EventControl", PRIORITY_URGENT_DISPLAY);

// set a fake vsync period if there is no HWComposer
//hwc层初始化失败后，使用1/16666667的屏幕刷新周期
if (mHwc->initCheck() != NO_ERROR) {
mPrimaryDispSync.setPeriod(16666667);
}

// initialize our drawing state
//初始化mDrawingState
mDrawingState = mCurrentState;

// set initial conditions (e.g. unblank default device)
//初始化主屏幕的一些flag和信息
initializeDisplays();

// start boot animation
//启动bootanimation
startBootAnim();
}
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先看看hwc的初始化。vsync信号分为两种：1.硬件产生的vsync；2.软件模拟的vsync。这份源码对应的是Android 5.1，使用的hwc HAL版本是1.4，所以不会打开framebuffer设备，在有hwc设备的情况下不会开启软件模拟vysnc。
而且硬件vsync一开始是出于关闭状态的。

/frameworks/native/services/surfaceflinger/DisplayHardware/HWComposer.cpp

HWComposer::HWComposer(
const sp<SurfaceFlinger>& flinger,
EventHandler& handler)
: mFlinger(flinger),
mFbDev(0), mHwc(0), mNumDisplays(1),
mCBContext(new cb_context),
mEventHandler(handler),
mDebugForceFakeVSync(false)
{
for (size_t i =0 ; i<MAX_HWC_DISPLAYS ; i++) {
mLists[i] = 0;
}

for (size_t i=0 ; i<HWC_NUM_PHYSICAL_DISPLAY_TYPES ; i++) {
mLastHwVSync[i] = 0;
mVSyncCounts[i] = 0;
}

char value[PROPERTY_VALUE_MAX];
property_get("debug.sf.no_hw_vsync", value, "0");
//mDebugForceFakeVSync决定我们是否启用硬件vsync，为true时永久关闭硬件vsync
mDebugForceFakeVSync = atoi(value);
//表示是否需要软件模拟vsync
bool needVSyncThread = true;

// Note: some devices may insist that the FB HAL be opened before HWC.
//加载framebuffer和hwc的HAL模块
int fberr = loadFbHalModule();
loadHwcModule();

if (mFbDev && mHwc && hwcHasApiVersion(mHwc, HWC_DEVICE_API_VERSION_1_1)) {
// close FB HAL if we don't needed it.
// FIXME: this is temporary until we're not forced to open FB HAL
// before HWC.
//如果framebuffer和hwc的硬件设备都被成功加载，且hwc HAL版本大于等于1.1，关闭framebuffer硬件设备
framebuffer_close(mFbDev);
mFbDev = NULL;
}

// If we have no HWC, or a pre-1.1 HWC, an FB dev is mandatory.
if ((!mHwc || !hwcHasApiVersion(mHwc, HWC_DEVICE_API_VERSION_1_1))
&& !mFbDev) {
ALOGE("ERROR: failed to open framebuffer (%s), aborting",
strerror(-fberr));
abort();
}

// these display IDs are always reserved
//NUM_BUILTIN_DISPLAYS（2）以内的id已被占用，申请hwc id需要从NUM_BUILTIN_DISPLAYS开始申请
for (size_t i=0 ; i<NUM_BUILTIN_DISPLAYS ; i++) {
mAllocatedDisplayIDs.markBit(i);
}

if (mHwc) {
ALOGI("Using %s version %u.%u", HWC_HARDWARE_COMPOSER,
(hwcApiVersion(mHwc) >> 24) & 0xff,
(hwcApiVersion(mHwc) >> 16) & 0xff);
if (mHwc->registerProcs) {
//注册hwc HAL层回调事件
mCBContext->hwc = this;
mCBContext->procs.invalidate = &hook_invalidate;
mCBContext->procs.vsync = &hook_vsync;
if (hwcHasApiVersion(mHwc, HWC_DEVICE_API_VERSION_1_1))
mCBContext->procs.hotplug = &hook_hotplug;
else
mCBContext->procs.hotplug = NULL;
memset(mCBContext->procs.zero, 0, sizeof(mCBContext->procs.zero));
mHwc->registerProcs(mHwc, &mCBContext->procs);
}

// don't need a vsync thread if we have a hardware composer
//有hwc模块就不需要软件模拟vysnc了
needVSyncThread = false;
// always turn vsync off when we start
//hwc初始化时先关闭硬件vysnc
eventControl(HWC_DISPLAY_PRIMARY, HWC_EVENT_VSYNC, 0);

// the number of displays we actually have depends on the
// hw composer version
if (hwcHasApiVersion(mHwc, HWC_DEVICE_API_VERSION_1_3)) {
// 1.3 adds support for virtual displays
mNumDisplays = MAX_HWC_DISPLAYS;
} else if (hwcHasApiVersion(mHwc, HWC_DEVICE_API_VERSION_1_1)) {
// 1.1 adds support for multiple displays
mNumDisplays = NUM_BUILTIN_DISPLAYS;
} else {
mNumDisplays = 1;
}
}

if (mFbDev) {
//hwc HAL1.1以上的版本mFbDev为null,不会走到该分支
ALOG_ASSERT(!(mHwc && hwcHasApiVersion(mHwc, HWC_DEVICE_API_VERSION_1_1)),
"should only have fbdev if no hwc or hwc is 1.0");

DisplayData& disp(mDisplayData[HWC_DISPLAY_PRIMARY]);
disp.connected = true;
disp.format = mFbDev->format;
DisplayConfig config = DisplayConfig();
config.width = mFbDev->width;
config.height = mFbDev->height;
config.xdpi = mFbDev->xdpi;
config.ydpi = mFbDev->ydpi;
config.refresh = nsecs_t(1e9 / mFbDev->fps);
disp.configs.push_back(config);
disp.currentConfig = 0;
} else if (mHwc) {
// here we're guaranteed to have at least HWC 1.1
//执行到这里说明是hwc HAL1.1以上的版本，这里从HAL层获取屏幕信息填充mDisplayData成员变量
for (size_t i =0 ; i<NUM_BUILTIN_DISPLAYS ; i++) {
queryDisplayProperties(i);
}
}

if (needVSyncThread) {
// we don't have VSYNC support, we need to fake it
//不支持硬件vsyn，就开启软件模拟vysnc线程
mVSyncThread = new VSyncThread(*this);
}
}
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再看看DisplayDevice的初始化。

/frameworks/native/services/surfaceflinger/DisplayDevice.cpp

DisplayDevice::DisplayDevice(
const sp<SurfaceFlinger>& flinger,
DisplayType type,
int32_t hwcId,
int format,
bool isSecure,
const wp<IBinder>& displayToken,
const sp<DisplaySurface>& displaySurface,
const sp<IGraphicBufferProducer>& producer,
EGLConfig config)
: lastCompositionHadVisibleLayers(false),
mFlinger(flinger),
mType(type), mHwcDisplayId(hwcId),
mDisplayToken(displayToken),
mDisplaySurface(displaySurface),
mDisplay(EGL_NO_DISPLAY),
mSurface(EGL_NO_SURFACE),
mDisplayWidth(), mDisplayHeight(), mFormat(),
mFlags(),
mPageFlipCount(),
mIsSecure(isSecure),
mSecureLayerVisible(false),
mLayerStack(NO_LAYER_STACK),
mOrientation(),
mPowerMode(HWC_POWER_MODE_OFF),
mActiveConfig(0)
{
//DisplayDevice新建一个Surface作为生产者
mNativeWindow = new Surface(producer, false);
ANativeWindow* const window = mNativeWindow.get();

/*
* Create our display's surface
*/

EGLSurface surface;
EGLint w, h;
EGLDisplay display = eglGetDisplay(EGL_DEFAULT_DISPLAY);
if (config == EGL_NO_CONFIG) {
config = RenderEngine::chooseEglConfig(display, format);
}
//创建EGLSurface
surface = eglCreateWindowSurface(display, config, window, NULL);
//获取Surface的宽高，保存在mDisplayWidth和mDisplayHeight中，这两个值在消费者FrameBufferSurfcae创建时从hwc HAL层获得，就是屏幕的宽高值
eglQuerySurface(display, surface, EGL_WIDTH, &mDisplayWidth);
eglQuerySurface(display, surface, EGL_HEIGHT, &mDisplayHeight);

// Make sure that composition can never be stalled by a virtual display
// consumer that isn't processing buffers fast enough. We have to do this
// in two places:
// * Here, in case the display is composed entirely by HWC.
// * In makeCurrent(), using eglSwapInterval. Some EGL drivers set the
// window's swap interval in eglMakeCurrent, so they'll override the
// interval we set here.
if (mType >= DisplayDevice::DISPLAY_VIRTUAL)
window->setSwapInterval(window, 0);

mConfig = config;
mDisplay = display;
mSurface = surface;
mFormat = format;
mPageFlipCount = 0;
mViewport.makeInvalid();
mFrame.makeInvalid();

// virtual displays are always considered enabled
//主屏幕的电源模式初始化为关闭状态，在SurfaceFlinger::onInitializeDisplays中，会将主屏幕的电源模式设为HWC_POWER_MODE_NORMAL
mPowerMode = (mType >= DisplayDevice::DISPLAY_VIRTUAL) ?
HWC_POWER_MODE_NORMAL : HWC_POWER_MODE_OFF;

// Name the display. The name will be replaced shortly if the display
// was created with createDisplay().
switch (mType) {
case DISPLAY_PRIMARY:
mDisplayName = "Built-in Screen";
break;
case DISPLAY_EXTERNAL:
mDisplayName = "HDMI Screen";
break;
default:
mDisplayName = "Virtual Screen"; // e.g. Overlay #n
break;
}

// initialize the display orientation transform.
//调整显示设备视角的大小、位移、旋转等参数，eOrientationDefault指的是默认的旋转方向，mViewport指的是逻辑显示区域，mFrame指的是物理显示区域
setProjection(DisplayState::eOrientationDefault, mViewport, mFrame);
}
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再看看双EventThread的初始化。我们可以在基于物理vsync的基础上添加相移，作为独立的vsync起始位置mPhase，再根据vsync的周期mPeriod，可以独立就算出一个独立的vsync模型，供app和SurfaceFlinger两个EventThread使用。而且还可以在后续的过程中动态更新这个vsync模型，这样做可以使物理vsync，app绘制下一帧，SurfaceFlinger合成图层错开工作，避免同一时间同时执行这三个操作，提高效率。
vsyncPhaseOffsetNs是app端的DispSyncSource使用的相移mPhase由VSYNC_EVENT_PHASE_OFFSET_NS宏指定，可以在在mk文件加入LOCAL_CFLAGS := -DVSYNC_EVENT_PHASE_OFFSET_NS=xxx指定；而SurfaceFlinger端使用的相移SF_VSYNC_EVENT_PHASE_OFFSET_NS则由SF_VSYNC_EVENT_PHASE_OFFSET_NS指定，也可以在mk文件中指定。而mPeriod在两个DispSyncSource构建时为0。

/frameworks/native/services/surfaceflinger/SurfaceFlinger.cpp

// start the EventThread
sp<VSyncSource> vsyncSrc = new DispSyncSource(&mPrimaryDispSync,
vsyncPhaseOffsetNs, true, "app");
mEventThread = new EventThread(vsyncSrc);
sp<VSyncSource> sfVsyncSrc = new DispSyncSource(&mPrimaryDispSync,
sfVsyncPhaseOffsetNs, true, "sf");
mSFEventThread = new EventThread(sfVsyncSrc);
mEventQueue.setEventThread(mSFEventThread);
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mPrimaryDispSync是一个DispSync对象，其在构造时会执行一个DispSyncThread线程。该线程负责在使能vync的时候执行一些回调操作，从而触发更新图层或者app绘制下一帧的动作。这个在以后篇幅再介绍。

/frameworks/native/services/surfaceflinger/DispSync.cpp

DispSync::DispSync() :
mRefreshSkipCount(0),
mThread(new DispSyncThread()) {

mThread->run("DispSync", PRIORITY_URGENT_DISPLAY + PRIORITY_MORE_FAVORABLE);

reset();
beginResync();

if (kTraceDetailedInfo) {
// If we're not getting present fences then the ZeroPhaseTracer
// would prevent HW vsync event from ever being turned off.
// Even if we're just ignoring the fences, the zero-phase tracing is
// not needed because any time there is an event registered we will
// turn on the HW vsync events.
if (!kIgnorePresentFences) {
addEventListener(0, new ZeroPhaseTracer());
}
}
}
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SurfaceFlinger::initializeDisplays用来初始化一些状态。

/frameworks/native/services/surfaceflinger/SurfaceFlinger.cpp

void SurfaceFlinger::initializeDisplays() {
class MessageScreenInitialized : public MessageBase {
SurfaceFlinger* flinger;
public:
MessageScreenInitialized(SurfaceFlinger* flinger) : flinger(flinger) { }
virtual bool handler() {
flinger->onInitializeDisplays();
return true;
}
};
sp<MessageBase> msg = new MessageScreenInitialized(this);
postMessageAsync(msg); // we may be called from main thread, use async message
}
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DisplayState用来记录一个屏幕设备的状态信息。这里将主屏幕的变化flag设为eDisplayProjectionChanged |eLayerStackChanged；将layerStack 设为0（通常一个屏幕对应一个layerstack）；将orientation设为默认旋转方向等等。这些信息都会被封装到DisplayState中，这个DisplayState会被添加到装载DisplayState的vector displays中，通过setTransactionState–>setDisplayStateLocked传递给mCurrentState的displays成员。SurfaceFlinger维持了两个成员变量mCurrentState和mDrawingState，mCurrentState记录了SurfaceFlinger当前屏幕的相关信息，mDrawingState记录了上一次更新图层时屏幕的相关信息。通过对比mCurrentState和mDrawingState，可以知道屏幕的哪些参数发生了改变，并更新这些信息到mCurrentState中。如果发生了变化，还会触发一次signalTransaction以更新图层。

/frameworks/native/services/surfaceflinger/SurfaceFlinger.cpp

void SurfaceFlinger::onInitializeDisplays() {
// reset screen orientation and use primary layer stack
Vector<ComposerState> state;
Vector<DisplayState> displays;
DisplayState d;
d.what = DisplayState::eDisplayProjectionChanged |
DisplayState::eLayerStackChanged;
d.token = mBuiltinDisplays[DisplayDevice::DISPLAY_PRIMARY];
d.layerStack = 0;
d.orientation = DisplayState::eOrientationDefault;
d.frame.makeInvalid();
d.viewport.makeInvalid();
d.width = 0;
d.height = 0;
displays.add(d);
setTransactionState(state, displays, 0);
setPowerModeInternal(getDisplayDevice(d.token), HWC_POWER_MODE_NORMAL);

const nsecs_t period =
getHwComposer().getRefreshPeriod(HWC_DISPLAY_PRIMARY);
mAnimFrameTracker.setDisplayRefreshPeriod(period);
}
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/frameworks/native/services/surfaceflinger/SurfaceFlinger.cpp

void SurfaceFlinger::setTransactionState(
const Vector<ComposerState>& state,
const Vector<DisplayState>& displays,
uint32_t flags)
{
ATRACE_CALL();
Mutex::Autolock _l(mStateLock);
uint32_t transactionFlags = 0;

if (flags & eAnimation) {
// For window updates that are part of an animation we must wait for
// previous animation "frames" to be handled.
while (mAnimTransactionPending) {
status_t err = mTransactionCV.waitRelative(mStateLock, s2ns(5));
if (CC_UNLIKELY(err != NO_ERROR)) {
// just in case something goes wrong in SF, return to the
// caller after a few seconds.
ALOGW_IF(err == TIMED_OUT, "setTransactionState timed out "
"waiting for previous animation frame");
mAnimTransactionPending = false;
break;
}
}
}

size_t count = displays.size();
for (size_t i=0 ; i<count ; i++) {
const DisplayState& s(displays[i]);
//更新屏幕信息到mCurrentState
transactionFlags |= setDisplayStateLocked(s);
}

count = state.size();
for (size_t i=0 ; i<count ; i++) {
const ComposerState& s(state[i]);
// Here we need to check that the interface we're given is indeed
// one of our own. A malicious client could give us a NULL
// IInterface, or one of its own or even one of our own but a
// different type. All these situations would cause us to crash.
//
// NOTE: it would be better to use RTTI as we could directly check
// that we have a Client*. however, RTTI is disabled in Android.
if (s.client != NULL) {
sp<IBinder> binder = s.client->asBinder();
if (binder != NULL) {
String16 desc(binder->getInterfaceDescriptor());
if (desc == ISurfaceComposerClient::descriptor) {
sp<Client> client( static_cast<Client *>(s.client.get()) );
transactionFlags |= setClientStateLocked(client, s.state);
}
}
}
}

if (transactionFlags) {
// this triggers the transaction
//屏幕信息发生了变化，触发更新图层
setTransactionFlags(transactionFlags);

// if this is a synchronous transaction, wait for it to take effect
// before returning.
if (flags & eSynchronous) {
mTransactionPending = true;
}
if (flags & eAnimation) {
mAnimTransactionPending = true;
}
while (mTransactionPending) {
status_t err = mTransactionCV.waitRelative(mStateLock, s2ns(5));
if (CC_UNLIKELY(err != NO_ERROR)) {
// just in case something goes wrong in SF, return to the
// called after a few seconds.
ALOGW_IF(err == TIMED_OUT, "setTransactionState timed out!");
mTransactionPending = false;
break;
}
}
}
}
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/frameworks/native/services/surfaceflinger/SurfaceFlinger.cpp

uint32_t SurfaceFlinger::setDisplayStateLocked(const DisplayState& s)
{
ssize_t dpyIdx = mCurrentState.displays.indexOfKey(s.token);
if (dpyIdx < 0)
return 0;

uint32_t flags = 0;
DisplayDeviceState& disp(mCurrentState.displays.editValueAt(dpyIdx));
if (disp.isValid()) {
const uint32_t what = s.what;
if (what & DisplayState::eSurfaceChanged) {
if (disp.surface->asBinder() != s.surface->asBinder()) {
disp.surface = s.surface;
flags |= eDisplayTransactionNeeded;
}
}
if (what & DisplayState::eLayerStackChanged) {
if (disp.layerStack != s.layerStack) {
disp.layerStack = s.layerStack;
flags |= eDisplayTransactionNeeded;
}
}
if (what & DisplayState::eDisplayProjectionChanged) {
if (disp.orientation != s.orientation) {
disp.orientation = s.orientation;
flags |= eDisplayTransactionNeeded;
}
if (disp.frame != s.frame) {
disp.frame = s.frame;
flags |= eDisplayTransactionNeeded;
}
if (disp.viewport != s.viewport) {
disp.viewport = s.viewport;
flags |= eDisplayTransactionNeeded;
}
}
if (what & DisplayState::eDisplaySizeChanged) {
if (disp.width != s.width) {
disp.width = s.width;
flags |= eDisplayTransactionNeeded;
}
if (disp.height != s.height) {
disp.height = s.height;
flags |= eDisplayTransactionNeeded;
}
}
}
return flags;
}
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/frameworks/native/services/surfaceflinger/SurfaceFlinger.cpp

void SurfaceFlinger::setPowerModeInternal(const sp<DisplayDevice>& hw,
int mode) {
ALOGD("Set power mode=%d, type=%d flinger=%p", mode, hw->getDisplayType(),
this);
int32_t type = hw->getDisplayType();
int currentMode = hw->getPowerMode();

if (mode == currentMode) {
ALOGD("Screen type=%d is already mode=%d", hw->getDisplayType(), mode);
return;
}

hw->setPowerMode(mode);
if (type >= DisplayDevice::NUM_BUILTIN_DISPLAY_TYPES) {
ALOGW("Trying to set power mode for virtual display");
return;
}

if (currentMode == HWC_POWER_MODE_OFF) {
getHwComposer().setPowerMode(type, mode);
if (type == DisplayDevice::DISPLAY_PRIMARY) {
// FIXME: eventthread only knows about the main display right now
mEventThread->onScreenAcquired();
resyncToHardwareVsync(true);
}

mVisibleRegionsDirty = true;
repaintEverything();
} else if (mode == HWC_POWER_MODE_OFF) {
if (type == DisplayDevice::DISPLAY_PRIMARY) {
disableHardwareVsync(true); // also cancels any in-progress resync

// FIXME: eventthread only knows about the main display right now
mEventThread->onScreenReleased();
}

getHwComposer().setPowerMode(type, mode);
mVisibleRegionsDirty = true;
// from this point on, SF will stop drawing on this display
} else {
getHwComposer().setPowerMode(type, mode);
}
}
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:initializeDisplays还有一步操作是设置DisplayDevice的PowerMode。主屏幕初始化时的PowerMode为HWC_POWER_MODE_OFF，现在要更新为HWC_POWER_MODE_NORMAL。

/frameworks/native/services/surfaceflinger/SurfaceFlinger.cpp

if (mode == currentMode) {
ALOGD("Screen type=%d is already mode=%d", hw->getDisplayType(), mode);
return;
}
//更新DisplayDevice的PowerMode
hw->setPowerMode(mode);
if (type >= DisplayDevice::NUM_BUILTIN_DISPLAY_TYPES) {
ALOGW("Trying to set power mode for virtual display");
return;
}

if (currentMode == HWC_POWER_MODE_OFF) {
//设置hwc的PowerMode
getHwComposer().setPowerMode(type, mode);
if (type == DisplayDevice::DISPLAY_PRIMARY) {
// FIXME: eventthread only knows about the main display right now
mEventThread->onScreenAcquired();
//需要打开硬件vsync同步
resyncToHardwareVsync(true);
}

mVisibleRegionsDirty = true;
//触发重绘操作
repaintEverything();
} else if (mode == HWC_POWER_MODE_OFF) {
if (type == DisplayDevice::DISPLAY_PRIMARY) {
disableHardwareVsync(true); // also cancels any in-progress resync

// FIXME: eventthread only knows about the main display right now
mEventThread->onScreenReleased();
}

getHwComposer().setPowerMode(type, mode);
mVisibleRegionsDirty = true;
// from this point on, SF will stop drawing on this display
} else {
getHwComposer().setPowerMode(type, mode);
}
}
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这里会更新vysnc周期mPeriod为hwc层的硬件Vysnc周期，一般为1/60s，因为从灭屏状态进入到点亮屏幕状态需要重建vsync模型。mPrimaryHWVsyncEnabled被初始化为false，所以通过EventControlThread::setVsyncEnabled就可以打开硬件Vsync了，从此开始进入Vsync的世界。

/frameworks/native/services/surfaceflinger/SurfaceFlinger.cpp

void SurfaceFlinger::resyncToHardwareVsync(bool makeAvailable) {
Mutex::Autolock _l(mHWVsyncLock);

if (makeAvailable) {
mHWVsyncAvailable = true;
} else if (!mHWVsyncAvailable) {
ALOGE("resyncToHardwareVsync called when HW vsync unavailable");
return;
}

const nsecs_t period =
getHwComposer().getRefreshPeriod(HWC_DISPLAY_PRIMARY);

mPrimaryDispSync.reset();
mPrimaryDispSync.setPeriod(period);

if (!mPrimaryHWVsyncEnabled) {
mPrimaryDispSync.beginResync();
//eventControl(HWC_DISPLAY_PRIMARY, SurfaceFlinger::EVENT_VSYNC, true);
mEventControlThread->setVsyncEnabled(true);
mPrimaryHWVsyncEnabled = true;
}
}
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SurfaceFlinger初始化的最后一步是启动bootanimation，由于跟原理无关，先略去。
---------------------
作者：Invoker123
来源：CSDN
原文：https://blog.csdn.net/invoker123/article/details/82470413
版权声明：本文为博主原创文章，转载请附上博文链接！

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