Android显示系统SurfaceFlinger详解超级干货

04-27 1130阅读 0评论

本文详细讲解了Android显示系统SurfaceFlinger，文中通过示例代码介绍的非常详细。对大家的学习或工作具有一定的参考借鉴价值，需要的朋友可以参考下

1.【执行文件-surfaceflinger】
2.【动态库-libsurfaceflinger.so】
3. 服务启动配置文件：/frameworks/native/services/surfaceflinger/surfaceflinger.rc
4. Surface 创建过程
- ①FramebufferNativeWindow
- ②应用程序的本地窗口 - Surface
- ③Surface的创建
- ④SurfaceFlinger服务框架：

一、Android系统启动

Android设备从按下开机键到桌面显示画面，大致过程如下图流程：

开机显示桌面、从桌面点击 App 图标到 Activity显示在屏幕上的过程又是怎样的呢？下面介绍Android系统中的“画家” - SurfaceFlinger.

SurfaceFlinger 启动过程：

二、SurfaceFlinger代码剖析[Android 11]

代码路径：/frameworks/native/services/surfaceflinger/

SurfaceFlinger二进制分成surfaceflinger可执行文件（main入口）和libsurfaceflinger.so库文件（功能实现），由main_surfaceflinger.cpp文件编译而成，Android.bp代码模块编译配置如下：

1.【执行文件-surfaceflinger】

...cc_binary {

name: "surfaceflinger",

defaults: ["surfaceflinger_defaults"],

init_rc: ["surfaceflinger.rc"],

srcs: ["main_surfaceflinger.cpp"],

whole_static_libs: [

"libsigchain",

shared_libs: [

"android.frameworks.displayservice@1.0",

"android.hardware.configstore-utils",

"android.hardware.configstore@1.0",

"android.hardware.graphics.allocator@2.0",

"libbinder",

"libcutils",

"libdisplayservicehidl",

"libhidlbase",

"libhidltransport",

"liblayers_proto",

"liblog",

"libsurfaceflinger",

"libtimestats_proto",

"libutils",

static_libs: [

"libserviceutils",

"libtrace_proto",

ldflags: ["-Wl,--export-dynamic"],

// TODO(b/71715793): These version-scripts are required due to the use of

// whole_static_libs to pull in libsigchain. To work, the files had to be

// locally duplicated from their original location

// $ANDROID_ROOT/art/sigchainlib/

multilib: {

lib32: {

version_script: "version-script32.txt",

lib64: {

version_script: "version-script64.txt",

}...

SurfaceFlinger可执行二进制文件surfaceflinger由main_surfaceflinger.cpp文件独立编译而成，主要负责搭建进程启动环境：

int main(int, char**) {

signal(SIGPIPE, SIG_IGN);

// 从8.0开始，Android提供了hidl机制，将原先直接由JNI->Native->HAL的接口调用形式，统一规范成hidl service/client交互形式。

// 该方式从一方面规范和统一了Android Framework和HAL的调用机制，但实际从项目维度，这种调用方式对性能上开销，将比直接调用的方式要花费更多的时间。

hardware::configureRpcThreadpool(1 /* maxThreads */,

false /* callerWillJoin */);

startGraphicsAllocatorService();

// When SF is launched in its own process, limit the number of

// binder threads to 4.

ProcessState::self()->setThreadPoolMaxThreadCount(4);

// start the thread pool

sp ps(ProcessState::self());

ps->startThreadPool();

// 创建SurfaceFlinger对象，由强指针指向。

// SurfaceFlinger继承RefBase类，所以此处一旦new出对象赋给sp指针后，将立刻出发SurfaceFlinger类的onFirstRef方法的调用。

// instantiate surfaceflinger

sp flinger = surfaceflinger::createSurfaceFlinger();

setpriority(PRIO_PROCESS, 0, PRIORITY_URGENT_DISPLAY);

set_sched_policy(0, SP_FOREGROUND);

// Put most SurfaceFlinger threads in the system-background cpuset

// Keeps us from unnecessarily using big cores

// Do this after the binder thread pool init

if (cpusets_enabled()) set_cpuset_policy(0, SP_SYSTEM);

// SurfaceFlinger类正式初始化

// initialize before clients can connect

flinger->init();

// SurfaceFlinger向ServiceManager注册Binder服务，

// 这样在其他进程中可以通过getService+SERVICE_NAME来获取SurfaceFlinger服务，继而可以和SurfaceFlinger类进行Binder通信。

// publish surface flinger

sp sm(defaultServiceManager());

sm->addService(String16(SurfaceFlinger::getServiceName()), flinger, false,

IServiceManager::DUMP_FLAG_PRIORITY_CRITICAL | IServiceManager::DUMP_FLAG_PROTO);

//里面的new DisplayService()方法调用HIDL定义接口 Return getEventReceiver() override;

startDisplayService(); // dependency on SF getting registered above

if (SurfaceFlinger::setSchedFifo(true) != NO_ERROR) {

ALOGW("Couldn't set to SCHED_FIFO: %s", strerror(errno));

}

// SurfaceFlinger类进入主循环（此处注意SurfaceFlinger类未继承Threads类，不遵循Threads类的接口执行顺序）

// run surface flinger in this thread

flinger->run();

return 0;

}

HIDL接口介绍可以参考：HIDL 接口文档 | Android 开源项目 | Android Open Source Project

2.【动态库-libsurfaceflinger.so】

Android.bp代码模块编译配置如下：

...cc_library_shared {

name: "libsurfaceflinger",

defaults: ["libsurfaceflinger_defaults"],

cflags: [

"-fvisibility=hidden",

"-Werror=format",

"-DREDUCE_VIDEO_WORKLOAD",

"-DUSE_AML_HW_ACTIVE_MODE",

srcs: [

":libsurfaceflinger_sources",

logtags: ["EventLog/EventLogTags.logtags"],

include_dirs: [

"frameworks/native/vulkan/vkjson",

"frameworks/native/vulkan/include",

"hardware/amlogic/gralloc/amlogic",

"hardware/amlogic/hwcomposer/tvp",

"hardware/amlogic/gralloc",

static_libs: [

"libomxutils_static@2",

"libamgralloc_ext_static@2",

cppflags: [

"-fwhole-program-vtables", // requires ThinLTO

lto: {

thin: true,

}...

上面提到的createSurfaceFlinger()中会调用new SurfaceFlinger()，然后会执行到：onFirstRef()：

void SurfaceFlinger::onFirstRef()

{

mEventQueue.init(this);

}

onFirstRef() 中会创建 Handler 并初始化: /frameworks/native/services/surfaceflinger/Scheduler/MessageQueue.cpp

//MessageQueue.cpp

void MessageQueue::init(const sp& flinger)

{

mFlinger = flinger;

mLooper = new Looper(true);

mHandler = new Handler(*this);

}

然后会执行到 SurfaceFlinger::init()，该方法主要功能是：

初始化 EGL
创建 HWComposer
初始化非虚拟显示屏
启动 EventThread 线程

启动开机动画

// Do not call property_set on main thread which will be blocked by init

// Use StartPropertySetThread instead.

void SurfaceFlinger::init() {

ALOGI( "SurfaceFlinger's main thread ready to run. "

"Initializing graphics H/W...");

Mutex::Autolock _l(mStateLock);

// 对于CompositionEngine 属性进行设置，创建RenderEngine对象

// Get a RenderEngine for the given display / config (can't fail)

// TODO(b/77156734): We need to stop casting and use HAL types when possible.

// Sending maxFrameBufferAcquiredBuffers as the cache size is tightly tuned to single-display.

mCompositionEngine->setRenderEngine(renderengine::RenderEngine::create(

renderengine::RenderEngineCreationArgs::Builder()

.setPixelFormat(static_cast(defaultCompositionPixelFormat))

.setImageCacheSize(maxFrameBufferAcquiredBuffers)

.setUseColorManagerment(useColorManagement)

.setEnableProtectedContext(enable_protected_contents(false))

.setPrecacheToneMapperShaderOnly(false)

.setSupportsBackgroundBlur(mSupportsBlur)

.setContextPriority(useContextPriority

? renderengine::RenderEngine::ContextPriority::HIGH

: renderengine::RenderEngine::ContextPriority::MEDIUM)

.build()));

mCompositionEngine->setTimeStats(mTimeStats);

LOG_ALWAYS_FATAL_IF(mVrFlingerRequestsDisplay,

"Starting with vr flinger active is not currently supported.");　　//创建HWComposer对象并传入一个name属性，再通过mCompositionEngine->setHwComposer设置对象属性。

mCompositionEngine->setHwComposer(getFactory().createHWComposer(getBE().mHwcServiceName));

mCompositionEngine->getHwComposer().setConfiguration(this, getBE().mComposerSequenceId);　　//processDisplayHotplugEventsLocked(); 处理任何初始热插拔和显示更改的结果　　//在此方法中主要有调用 initScheduler(displayId);

// Process any initial hotplug and resulting display changes.

processDisplayHotplugEventsLocked();

const auto display = getDefaultDisplayDeviceLocked();

LOG_ALWAYS_FATAL_IF(!display, "Missing internal display after registering composer callback.");

LOG_ALWAYS_FATAL_IF(!getHwComposer().isConnected(*display->getId()),

"Internal display is disconnected.");

if (useVrFlinger) {

auto vrFlingerRequestDisplayCallback = [this](bool requestDisplay) {

// This callback is called from the vr flinger dispatch thread. We

// need to call signalTransaction(), which requires holding

// mStateLock when we're not on the main thread. Acquiring

// mStateLock from the vr flinger dispatch thread might trigger a

// deadlock in surface flinger (see b/66916578), so post a message

// to be handled on the main thread instead.

static_cast(schedule([=] {

ALOGI("VR request display mode: requestDisplay=%d", requestDisplay);

mVrFlingerRequestsDisplay = requestDisplay;

signalTransaction();

}));

};

mVrFlinger = dvr::VrFlinger::Create(getHwComposer().getComposer(),

getHwComposer()

.fromPhysicalDisplayId(*display->getId())

.value_or(0),

vrFlingerRequestDisplayCallback);

if (!mVrFlinger) {

ALOGE("Failed to start vrflinger");

}

// initialize our drawing state

mDrawingState = mCurrentState;

// set initial conditions (e.g. unblank default device)

initializeDisplays();

char primeShaderCache[PROPERTY_VALUE_MAX];

property_get("service.sf.prime_shader_cache", primeShaderCache, "1");

if (atoi(primeShaderCache)) {

getRenderEngine().primeCache();

}

// Inform native graphics APIs whether the present timestamp is supported:

const bool presentFenceReliable =

!getHwComposer().hasCapability(hal::Capability::PRESENT_FENCE_IS_NOT_RELIABLE);

mStartPropertySetThread = getFactory().createStartPropertySetThread(presentFenceReliable);

if (mStartPropertySetThread->Start() != NO_ERROR) {

ALOGE("Run StartPropertySetThread failed!");

}

ALOGV("Done initializing");

}

首先看下如何创建 HWComposer：frameworks/native/services/surfaceflinger/SurfaceFlingerDefaultFactory.cpp

//make_unique 相当于 new,(能够取代new 而且无需 delete pointer，有助于代码管理)。

std::unique_ptr DefaultFactory::createHWComposer(const std::string& serviceName) {

return std::make_unique(serviceName);

}

对于CompositionEngine进行初始化:

std::unique_ptr DefaultFactory::createCompositionEngine() {

return compositionengine::impl::createCompositionEngine();

}

同样是通过make_unique创建了 CompositionEngine对象：

std::unique_ptr createCompositionEngine() {

return std::make_unique();

}

再回到flinger->init()中processDisplayHotplugEventsLocked(); 处理任何初始热插拔和显示更改的结果，在此方法中主要有调用 initScheduler(displayId)：

void SurfaceFlinger::initScheduler(DisplayId primaryDisplayId) {

if (mScheduler) {

// In practice it's not allowed to hotplug in/out the primary display once it's been

// connected during startup, but some tests do it, so just warn and return.

ALOGW("Can't re-init scheduler");

return;

}

auto currentConfig = HwcConfigIndexType(getHwComposer().getActiveConfigIndex(primaryDisplayId));

mRefreshRateConfigs =

std::make_unique(getHwComposer().getConfigs(

primaryDisplayId),

currentConfig);

mRefreshRateStats =

std::make_unique(*mRefreshRateConfigs, *mTimeStats,

currentConfig, hal::PowerMode::OFF);

mRefreshRateStats->setConfigMode(currentConfig);

mPhaseConfiguration = getFactory().createPhaseConfiguration(*mRefreshRateConfigs);

　　 // 处创建Scheduler对象

// start the EventThread

mScheduler =

getFactory().createScheduler([this](bool enabled) { setPrimaryVsyncEnabled(enabled); },

*mRefreshRateConfigs, *this);

//创建app链接和 sf链接 mAppConnectionHandle =

mScheduler->createConnection("app", mPhaseConfiguration->getCurrentOffsets().late.app,

impl::EventThread::InterceptVSyncsCallback());

mSfConnectionHandle =

mScheduler->createConnection("sf", mPhaseConfiguration->getCurrentOffsets().late.sf,

[this](nsecs_t timestamp) {

mInterceptor->saveVSyncEvent(timestamp);

});

mEventQueue->setEventConnection(mScheduler->getEventConnection(mSfConnectionHandle));

mVSyncModulator.emplace(*mScheduler, mAppConnectionHandle, mSfConnectionHandle,

mPhaseConfiguration->getCurrentOffsets());

mRegionSamplingThread =

new RegionSamplingThread(*this, *mScheduler,

RegionSamplingThread::EnvironmentTimingTunables());

// Dispatch a config change request for the primary display on scheduler

// initialization, so that the EventThreads always contain a reference to a

// prior configuration.

// This is a bit hacky, but this avoids a back-pointer into the main SF

// classes from EventThread, and there should be no run-time binder cost

// anyway since there are no connected apps at this point.

const nsecs_t vsyncPeriod =

mRefreshRateConfigs->getRefreshRateFromConfigId(currentConfig).getVsyncPeriod();

mScheduler->onPrimaryDisplayConfigChanged(mAppConnectionHandle, primaryDisplayId.value,

currentConfig, vsyncPeriod);

}

详细看下app、sf的链接:

Scheduler::ConnectionHandle Scheduler::createConnection(

const char* connectionName, nsecs_t phaseOffsetNs,

impl::EventThread::InterceptVSyncsCallback interceptCallback) {

auto vsyncSource = makePrimaryDispSyncSource(connectionName, phaseOffsetNs);

auto eventThread = std::make_unique(std::move(vsyncSource), std::move(interceptCallback));

return createConnection(std::move(eventThread));

}

可以看到创建了DispSyncSource对象，且构造方法传入了四个值，dispSync对象，phaseOffset偏移量，traceVsync为true，name就是 app或 sf

DispSyncSource::DispSyncSource(DispSync* dispSync, nsecs_t phaseOffset, bool traceVsync,

const char* name)

: mName(name),

mValue(base::StringPrintf("VSYNC-%s", name), 0), //对mValue进行了赋值，systrace上我们看到的 VSYNC-app VSYNC-sf 标签就是它

mTraceVsync(traceVsync), //mTraceVsync为true,在onDispSyncEvent方法中

mVsyncOnLabel(base::StringPrintf("VsyncOn-%s", name)),

mDispSync(dispSync),

mPhaseOffset(base::StringPrintf("VsyncOffset-%s", name), phaseOffset) //对mPhaseOffset进行初始化 vsync信号到来时候，sf、app的偏移量

所以我们在systrace上面看到的 VSYNC-app/VSYNC-sf 驼峰 0 1变化，来源于这个。

创建EventThread对象，传入sf 或 app 相关联的vsyncSource对象:

1	auto eventThread = std::make_unique(std::move(vsyncSource), std::move(interceptCallback));

说明：

1）每个ConnectionHandle 对象里有个 id，作为 Scheduler 对象中 mConnections 属性（map）的键值，Connection 对象中又包含 ConnectionHandle、EventThreadConnection、EventThread 3个属性。
2）mScheduler->getEventConnection(mSfConnectionHandle) 中，以 mSfConnectionHandle 的 id 为键值，在 Scheduler 的 mConnections（unordered_map）中找到对应的Connection，并返回其 EventThreadConnection 成员属性。

3）getHwComposer().registerCallback() 中，依次调用 HwComposer、Device 的registerCallback() 方法，并在 Device 中将 SurfaceFlinger 对象封装到 ComposerCallbackBridge 中；对于封装后的对象，依次调用 Composer、IComposerClient 的 registerCallback() 方法，注入到 IComposerClient 的实现类中。

3. 服务启动配置文件：/frameworks/native/services/surfaceflinger/surfaceflinger.rc

上面发现服务配置文件也在Android.mk中被加载：LOCAL_INIT_RC := surfaceflinger.rc

service surfaceflinger /system/bin/surfaceflinger

class core animation

user system

group graphics drmrpc readproc

onrestart restart zygote

writepid /dev/stune/foreground/tasks

socket pdx/system/vr/display/client stream 0666 system graphics u:object_r:pdx_display_client_endpoint_socket:s0

socket pdx/system/vr/display/manager stream 0666 system graphics u:object_r:pdx_display_manager_endpoint_socket:s0

socket pdx/system/vr/display/vsync stream 0666 system graphics u:object_r:pdx_display_vsync_endpoint_socket:s0

4. Surface 创建过程

Surface 创建的过程就是 Activity 显示的过程，在 ActivityThread.handleResumeActivity() 中调用了 Activity.makeVisible()具体实现：

void makeVisible() {

if (!mWindowAdded) {

ViewManager wm = getWindowManager();//此处 getWindowManager 获取的是 WindowManagerImpl 对象

wm.addView(mDecor, getWindow().getAttributes());

mWindowAdded = true;

}

mDecor.setVisibility(View.VISIBLE);

}

WindowManagerImpl.java：

public void addView(@NonNull View view, @NonNull ViewGroup.LayoutParams params) {

applyDefaultToken(params);

mGlobal.addView(view, params, mDisplay, mParentWindow);

}

WindowManagerGlobal.java：

public void addView(View view, ViewGroup.LayoutParams params, Display display, Window parentWindow) {

...

final WindowManager.LayoutParams wparams = (WindowManager.LayoutParams) params;

//创建 ViewRootImpl

ViewRootImpl root = new ViewRootImpl(view.getContext(), display);

view.setLayoutParams(wparams);

mViews.add(view);

mRoots.add(root);

mParams.add(wparams);

//设置 View

root.setView(view, wparams, panelParentView);

...

}

创建 ViewRootImpl：

public ViewRootImpl(Context context, Display display) {

//获取 IWindowSession的代理类

this(context, display, WindowManagerGlobal.getWindowSession(),

false /* useSfChoreographer */);

}

WindowManagerGlobal.java：

@UnsupportedAppUsage

public static IWindowSession getWindowSession() {

synchronized (WindowManagerGlobal.class) {

if (sWindowSession == null) {

try {

// Emulate the legacy behavior. The global instance of InputMethodManager

// was instantiated here.

// TODO(b/116157766): Remove this hack after cleaning up @UnsupportedAppUsage

//获取 IMS 的代理类

InputMethodManager.ensureDefaultInstanceForDefaultDisplayIfNecessary();

IWindowManager windowManager = getWindowManagerService();

//经过 Binder 调用，最终调用 WMS

sWindowSession = windowManager.openSession(

new IWindowSessionCallback.Stub() {

@Override

public void onAnimatorScaleChanged(float scale) {

ValueAnimator.setDurationScale(scale);

}

});

} catch (RemoteException e) {

throw e.rethrowFromSystemServer();

}

return sWindowSession;

}

WindowManagerService.openSession：

// -------------------------------------------------------------

// IWindowManager API

// -------------------------------------------------------------

@Override

public IWindowSession openSession(IWindowSessionCallback callback) {

//创建session对象

return new Session(this, callback);

}

再次经过 Binder 将数据写回 app 进程，则获取的便是 Session 的代理对象 IWindowSession。

创建完 ViewRootImpl 对象后，接下来调用该对象的 setView() 方法:

ViewRootImpl：

public void setView(View view, WindowManager.LayoutParams attrs, View panelParentView) {

synchronized (this) {

requestLayout(); //详见下面分析

...

//通过 Binder调用，进入 system 进程的 Session

　　　　res = mWindowSession.addToDisplayAsUser(mWindow, mSeq, mWindowAttributes, 　　　　　　　　getHostVisibility(), mDisplay.getDisplayId(), userId, mTmpFrame, 　　　　　　　　mAttachInfo.mContentInsets, mAttachInfo.mStableInsets, 　　　　　　　　mAttachInfo.mDisplayCutout, inputChannel, 　　　　　　　　mTempInsets, mTempControls);

...

}

Session.java

@Override

public int addToDisplayAsUser(IWindow window, int seq, WindowManager.LayoutParams attrs,

int viewVisibility, int displayId, int userId, Rect outFrame,

Rect outContentInsets, Rect outStableInsets,

DisplayCutout.ParcelableWrapper outDisplayCutout, InputChannel outInputChannel,

InsetsState outInsetsState, InsetsSourceControl[] outActiveControls) {

//调用WMS的addWindow方法

return mService.addWindow(this, window, seq, attrs, viewVisibility, displayId, outFrame,

outContentInsets, outStableInsets, outDisplayCutout, outInputChannel,

outInsetsState, outActiveControls, userId);

}

WindowManagerService.java：

public int addWindow(Session session, IWindow client, int seq,

LayoutParams attrs, int viewVisibility, int displayId, Rect outFrame,

Rect outContentInsets, Rect outStableInsets,

DisplayCutout.ParcelableWrapper outDisplayCutout, InputChannel outInputChannel,

InsetsState outInsetsState, InsetsSourceControl[] outActiveControls,

int requestUserId) {

Arrays.fill(outActiveControls, null);

int[] appOp = new int[1];

final boolean isRoundedCornerOverlay = (attrs.privateFlags

& PRIVATE_FLAG_IS_ROUNDED_CORNERS_OVERLAY) != 0;

int res = mPolicy.checkAddPermission(attrs.type, isRoundedCornerOverlay, attrs.packageName,

appOp);

if (res != WindowManagerGlobal.ADD_OKAY) {

return res;

}

WindowState parentWindow = null;

final int callingUid = Binder.getCallingUid();

final int callingPid = Binder.getCallingPid();

final long origId = Binder.clearCallingIdentity();

final int type = attrs.type;

synchronized (mGlobalLock) {

if (!mDisplayReady) {

throw new IllegalStateException("Display has not been initialialized");

}

...

//创建 WindowState

final WindowState win = new WindowState(this, session, client, token, parentWindow,

appOp[0], seq, attrs, viewVisibility, session.mUid, userId,

session.mCanAddInternalSystemWindow);

if (win.mDeathRecipient == null) {

// Client has apparently died, so there is no reason to

// continue.

ProtoLog.w(WM_ERROR, "Adding window client %s"

+ " that is dead, aborting.", client.asBinder());

return WindowManagerGlobal.ADD_APP_EXITING;

}

if (win.getDisplayContent() == null) {

ProtoLog.w(WM_ERROR, "Adding window to Display that has been removed.");

return WindowManagerGlobal.ADD_INVALID_DISPLAY;

}

// 调整 WindowManager的LayoutParams 参数

final DisplayPolicy displayPolicy = displayContent.getDisplayPolicy();

displayPolicy.adjustWindowParamsLw(win, win.mAttrs, callingPid, callingUid);

res = displayPolicy.validateAddingWindowLw(attrs, callingPid, callingUid);

if (res != WindowManagerGlobal.ADD_OKAY) {

return res;

}

// 打开输入通道

final boolean openInputChannels = (outInputChannel != null

&& (attrs.inputFeatures & INPUT_FEATURE_NO_INPUT_CHANNEL) == 0);

if (openInputChannels) {

win.openInputChannel(outInputChannel);

}

...

displayContent.getInputMonitor().setUpdateInputWindowsNeededLw();

boolean focusChanged = false;

//当该窗口能接收按键事件，则更新聚焦窗口

if (win.canReceiveKeys()) {

focusChanged = updateFocusedWindowLocked(UPDATE_FOCUS_WILL_ASSIGN_LAYERS,

false /*updateInputWindows*/);

if (focusChanged) {

imMayMove = false;

}

if (imMayMove) {

displayContent.computeImeTarget(true /* updateImeTarget */);

}

...

}

Binder.restoreCallingIdentity(origId);

return res;

}

创建 SurfaceSession 对象，并将当前 Session 添加到 WMS.mSessions 成员变量。

Session.java：

void windowAddedLocked(String packageName) {

mPackageName = packageName;

mRelayoutTag = "relayoutWindow: " + mPackageName;

if (mSurfaceSession == null) {

if (DEBUG) {

Slog.v(TAG_WM, "First window added to " + this + ", creating SurfaceSession");

}

mSurfaceSession = new SurfaceSession();

ProtoLog.i(WM_SHOW_TRANSACTIONS, " NEW SURFACE SESSION %s", mSurfaceSession);

mService.mSessions.add(this);

if (mLastReportedAnimatorScale != mService.getCurrentAnimatorScale()) {

mService.dispatchNewAnimatorScaleLocked(this);

}

mNumWindow++;

}

SurfaceSession 的创建会调用 JNI，在 JNI 调用 nativeCreate()。

android_view_SurfaceSession.cpp：

static jlong nativeCreate(JNIEnv* env, jclass clazz) {

SurfaceComposerClient* client = new SurfaceComposerClient();

client->incStrong((void*)nativeCreate);

return reinterpret_cast(client);

}

static jlong nativeCreate(JNIEnv* env, jclass clazz, jobject sessionObj,

jstring nameStr, jint w, jint h, jint format, jint flags, jlong parentObject,

jobject metadataParcel) {

ScopedUtfChars name(env, nameStr);

sp client;

if (sessionObj != NULL) {

client = android_view_SurfaceSession_getClient(env, sessionObj);

} else {

client = SurfaceComposerClient::getDefault();

}

SurfaceControl *parent = reinterpret_cast(parentObject);

sp surface;

LayerMetadata metadata;

Parcel* parcel = parcelForJavaObject(env, metadataParcel);

if (parcel && !parcel->objectsCount()) {

status_t err = metadata.readFromParcel(parcel);

if (err != NO_ERROR) {

jniThrowException(env, "java/lang/IllegalArgumentException",

"Metadata parcel has wrong format");

}

status_t err = client->createSurfaceChecked(

String8(name.c_str()), w, h, format, &surface, flags, parent, std::move(metadata));

if (err == NAME_NOT_FOUND) {

jniThrowException(env, "java/lang/IllegalArgumentException", NULL);

return 0;

} else if (err != NO_ERROR) {

jniThrowException(env, OutOfResourcesException, NULL);

return 0;

}

surface->incStrong((void *)nativeCreate);

return reinterpret_cast(surface.get());

}

通过以上JNI接口获取SurfaceComposerClient 对象，作为跟 SurfaceFlinger 通信的代理对象。

void SurfaceComposerClient::onFirstRef() {

//getComposerService() 将返回 SF 的 Binder 代理端的 BpSurfaceFlinger 对象

sp sf(ComposerService::getComposerService());

if (sf != nullptr && mStatus == NO_INIT) {

sp conn;

//调用 SF 的 createConnection()

conn = sf->createConnection();

if (conn != nullptr) {

mClient = conn;

mStatus = NO_ERROR;

}

比如截屏接口就会通过SurfaceControl调用到其中的capture 接口：

status_t ScreenshotClient::capture(const sp& display, ui::Dataspace reqDataSpace,

ui::PixelFormat reqPixelFormat, const Rect& sourceCrop,

uint32_t reqWidth, uint32_t reqHeight, bool useIdentityTransform,

ui::Rotation rotation, bool captureSecureLayers,

sp* outBuffer, bool& outCapturedSecureLayers) {

sp s(ComposerService::getComposerService());

if (s == nullptr) return NO_INIT;

status_t ret = s->captureScreen(display, outBuffer, outCapturedSecureLayers, reqDataSpace,

reqPixelFormat, sourceCrop, reqWidth, reqHeight,

useIdentityTransform, rotation, captureSecureLayers);

if (ret != NO_ERROR) {

return ret;

}

return ret;

}

然后具体看下核心的SurfaceFlinger实现：

SurfaceFlinger.cpp：

sp SurfaceFlinger::createConnection() {

//创建一个Client

const sp client = new Client(this);

return client->initCheck() == NO_ERROR ? client : nullptr;

}

回到之前，创建完 ViewRootImpl 对象后，接下来调用该对象的 setView() 方法。在 setView() 中调用了 requestLayout() 方法，现在具体来看下这个方法调用流程：

@Override

public void requestLayout() {

if (!mHandlingLayoutInLayoutRequest) {

checkThread();

mLayoutRequested = true;

scheduleTraversals();

}

@UnsupportedAppUsage

void scheduleTraversals() {

if (!mTraversalScheduled) {

mTraversalScheduled = true;

mTraversalBarrier = mHandler.getLooper().getQueue().postSyncBarrier();　　　　　　　//启动TraversalRunnable

mChoreographer.postCallback(

Choreographer.CALLBACK_TRAVERSAL, mTraversalRunnable, null);

notifyRendererOfFramePending();

pokeDrawLockIfNeeded();

}

final class TraversalRunnable implements Runnable {

@Override

public void run() {

doTraversal();

}

void doTraversal() {

if (mTraversalScheduled) {

mTraversalScheduled = false;

mHandler.getLooper().getQueue().removeSyncBarrier(mTraversalBarrier);

if (mProfile) {

Debug.startMethodTracing("ViewAncestor");

}

　　　　　　//调用performTraversals performTraversals();

if (mProfile) {

Debug.stopMethodTracing();

mProfile = false;

}

private void performTraversals() {

// cache mView since it is used so much below...

final View host = mView; //它就是 DecorView

...

if (mFirst || windowShouldResize || viewVisibilityChanged || cutoutChanged || params != null

|| mForceNextWindowRelayout) {

mForceNextWindowRelayout = false;

if (isViewVisible) {

// If this window is giving internal insets to the window

// manager, and it is being added or changing its visibility,

// then we want to first give the window manager "fake"

// insets to cause it to effectively ignore the content of

// the window during layout. This avoids it briefly causing

// other windows to resize/move based on the raw frame of the

// window, waiting until we can finish laying out this window

// and get back to the window manager with the ultimately

// computed insets.

insetsPending = computesInternalInsets && (mFirst || viewVisibilityChanged);

}

...

try {

if (DEBUG_LAYOUT) {

Log.i(mTag, "host=w:" + host.getMeasuredWidth() + ", h:" +

host.getMeasuredHeight() + ", params=" + params);

}

if (mAttachInfo.mThreadedRenderer != null) {

// relayoutWindow may decide to destroy mSurface. As that decision

// happens in WindowManager service, we need to be defensive here

// and stop using the surface in case it gets destroyed.

if (mAttachInfo.mThreadedRenderer.pause()) {

// Animations were running so we need to push a frame

// to resume them

mDirty.set(0, 0, mWidth, mHeight);

}

mChoreographer.mFrameInfo.addFlags(FrameInfo.FLAG_WINDOW_LAYOUT_CHANGED);

}

// 关键函数relayoutWindow

relayoutResult = relayoutWindow(params, viewVisibility, insetsPending);

if (DEBUG_LAYOUT) Log.v(mTag, "relayout: frame=" + frame.toShortString()

+ " cutout=" + mPendingDisplayCutout.get().toString()

+ " surface=" + mSurface);

// If the pending {@link MergedConfiguration} handed back from

// {@link #relayoutWindow} does not match the one last reported,

// WindowManagerService has reported back a frame from a configuration not yet

// handled by the client. In this case, we need to accept the configuration so we

// do not lay out and draw with the wrong configuration.

if (!mPendingMergedConfiguration.equals(mLastReportedMergedConfiguration)) {

if (DEBUG_CONFIGURATION) Log.v(mTag, "Visible with new config: "

+ mPendingMergedConfiguration.getMergedConfiguration());

performConfigurationChange(mPendingMergedConfiguration, !mFirst,

INVALID_DISPLAY /* same display */);

updatedConfiguration = true;

}

} catch (RemoteException e) {

}

...

}

boolean cancelDraw = mAttachInfo.mTreeObserver.dispatchOnPreDraw() || !isViewVisible;

if (!cancelDraw) {

if (mPendingTransitions != null && mPendingTransitions.size() > 0) {

for (int i = 0; i

mPendingTransitions.get(i).startChangingAnimations();

}

mPendingTransitions.clear();

}

//开始绘制，其中调用了draw(fullRedrawNeeded);

performDraw();

} else {

if (isViewVisible) {

// Try again

scheduleTraversals();

} else if (mPendingTransitions != null && mPendingTransitions.size() > 0) {

for (int i = 0; i

mPendingTransitions.get(i).endChangingAnimations();

}

mPendingTransitions.clear();

}

if (mAttachInfo.mContentCaptureEvents != null) {

notifyContentCatpureEvents();

}

mIsInTraversal = false;

}

再看下relayoutWindow的实现：

... if (mSurfaceControl.isValid()) {

if (!useBLAST()) {

//先创建一个本地Surface,然后调用copyFrom 将SurfaceControl信息拷贝到Surface中

mSurface.copyFrom(mSurfaceControl);

} else {

final Surface blastSurface = getOrCreateBLASTSurface(mSurfaceSize.x,

mSurfaceSize.y);

// If blastSurface == null that means it hasn't changed since the last time we

// called. In this situation, avoid calling transferFrom as we would then

// inc the generation ID and cause EGL resources to be recreated.

if (blastSurface != null) {

mSurface.transferFrom(blastSurface);

}

} else {

destroySurface();

}....

SurfaceControl 类可以看作是一个 wrapper 类，最后会执行 copyFrom() 将其返回给 App 客户端：

@UnsupportedAppUsage

public void copyFrom(SurfaceControl other) {

if (other == null) {

throw new IllegalArgumentException("other must not be null");

}

long surfaceControlPtr = other.mNativeObject;

if (surfaceControlPtr == 0) {

throw new NullPointerException(

"null SurfaceControl native object. Are you using a released SurfaceControl?");

}

//通过JNI获取源SurfaceControl

long newNativeObject = nativeGetFromSurfaceControl(mNativeObject, surfaceControlPtr);

synchronized (mLock) {

if (newNativeObject == mNativeObject) {

return;

}

if (mNativeObject != 0) {

nativeRelease(mNativeObject);

}

//保存到全局mNativeObject用于外部调用

setNativeObjectLocked(newNativeObject);

}

Surface 显示过程总结：

在 App 进程中创建 PhoneWindow 后会创建 ViewRoot。ViewRoot 的创建会创建一个 Surface，这个 Surface 其实是空的，通过与 WindowManagerService 通信 copyFrom() 一个NativeSurface 与 SurfaceFlinger 通信时。

关于Native Window：

Native Window是OpenGL与本地窗口系统之间搭建了桥梁。整个GUI系统至少需要两种本地窗口：

（1）面向管理者（SurfaceFlinger）
SurfaceFlinger是系统中所有UI界面的管理者，需要直接或间接的持有“本地窗口”，此本地窗口是FramebufferNativeWindow。
- （2）面向应用程序
  这类本地窗口是Surface。
  
  正常情况按照SDK向导生成APK应用程序，是采用Skia等第三方图形库，而对于希望使用OpenGL ES来完成复杂界面渲染的应用开发者来说，Android也提供封装的GLSurfaceView（或其他方式）来实现图形显示。
  
  ①FramebufferNativeWindow
  
  EGL需要通过本地窗口来为OpenGL/OpenGL ES创建环境。由于OpenGL/ES对多平台支持，考虑到兼容性和移植性。不同平台的本地窗口EGLNativeWindowType数据类型不同。
  
  Android平台的数据类型是ANativeWindow，像是一份“协议”，规定了一个本地窗口的形态和功能。ANativeWindow是FramebufferNativeWindow的父类。
  
  Android中，由于多缓冲技术，EGLNativeWindowType所管理的缓冲区最少2个，最大3个。
  
  FramebufferNativeWindow初始化需要Golloc支持，步骤如下：
  - 加载GRALLOC_HARDWARE_MODULE_ID模块，参见上节。
  - 分别打开fb和gralloc设备，打开后的设备由全局变量fbDev和grDev管理。
  - 根据设备的属性来给FramebufferNativeWindow赋初值。
  - 根据FramebufferNativeWindow的实现来填充ANativeWindow中的“协议”
  - 其他一些必要的初始化
    ②应用程序的本地窗口 - Surface
    
    Surface也继承了ANativeWindow
    
    1
    
    class Surface : public ANativeObjectBase
    
    Surface是面向Android系统中所有UI应用程序的，即它承担着应用进程中的UI显示需求。
    
    需要面向上层实现（主要是Java层）提供绘制图像的画板。SurfaceFlinger需要收集系统中所有应用程序绘制的图像数据，然后集中显示到物理屏幕上。Surface需要扮演相应角色，本质上还是由SurfaceFlinger服务统一管理的，涉及到很多跨进程的通信细节。
    
    ③Surface的创建
    
    Surface将通过mGraphicBufferProducer来获取buffer,这些缓冲区会被记录在mSlots中数据中。mGraphicBufferProducer这一核心成员的初始化流程如下：
    
    ViewRootImpl持有一个Java层的Surface对象（mSurface）。
    
    ViewRootImpl向WindowManagerService发起relayout请求，此时mSurface被赋予真正的有效值，将辗转生成的SurfaceControl通过Surface.copyFrom()函数复制到mSurface中。
    
    由此，Surface由SurfaceControl管理，SurfaceControl由SurfaceComposerClient创建。SurfaceComposerClient获得的匿名Binder是ISurfaceComposer，其服务端实现是SurfaceFlinger。而Surface依赖的IGraphicBufferProducer对象在Service端的实现是BufferQueue。
    
    1
    
    2
    
    3
    
    class SurfaceFlinger :
    
    public BinderService, //在ServiceManager中注册为SurfaceFlinger
    
    public BnSurfaceComposer,//实现的接口却叫ISurfaceComposer
    
    ④SurfaceFlinger服务框架：
    
    Buffer，Consumer，Producer是“生产者-消费者”模型中的3个参与对象，如何协调好它们的工作是应用程序能否正常显示UI的关键。
    
    Buffer是BufferQueue，Producer是应用程序，Consumer是SurfaceFlinger。
    
    Surface内部提供一个BufferQueue，与上层和SurfaceFlinger形成一个生产者消费者模型，上层对应Producer，SurfaceFlinger对应Consumer。三者通过Buffer产生联系，每个Buffer都有四种状态：
    - Free：可被上层使用;
    - Dequeued：出列，正在被上层使用;
    - Queued：入列，已完成上层绘制，等待SurfaceFlinger合成;
    - Acquired：被获取，SurfaceFlinger正持有该Buffer进行合成;
      如此循环，形成一个Buffer被循环使用的过程（FREE-> DEQUEUED->QUEUED->ACQUIRED->FREE）。
      
      BufferQueue中的mSlots数组用于管理期内的缓冲区，最大容器是32。数据缓冲区的空间是动态分配的，应用程序与SurfaceFlinger都是使用OpenGL ES来完成UI显示。Layer类在SurfaceFlinger中表示“层”，通俗地讲就是代表了一个“画面”，最终物理屏幕上的显示结果就是通过对系统中同时存在的所有“画面”进行处理叠加而成。
      
      到此这篇关于Android显示系统SurfaceFlinger详解的文章就介绍到这了。希望对大家的学习有所帮助，也希望大家多多支持脚本之家。