前言
经过上一篇文章的探索和学习，相信大家对Hal 层的运作原理以及SF如何监听Hal层返回的回调有一定的了解。
原本应该是聊如何申请图元的，但是感觉和前文的逻辑割裂有点大，还是继续按照SF初始化，开机的逻辑顺序继续走下去。这一次就让我们聊聊系统启动动画吧。
带着这个疑问去阅读，开机的时候没有Activity为什么可以播放开机动画呢？注意Android系统中存在几个开机动画，这里不去聊Linux开机动画，我们只聊Android渲染系统中的开机动画，也就是我们打开手机时候的那个动画。
如果遇到问题，可以到本文来讨论https://www.jianshu.com/p/a79de4a6d83c
正文
解析init.rc service的原理
文件：/frameworks/base/cmds/bootanimation/bootanim.rc
service bootanim /system/bin/bootanimation
class core animation
user graphics
group graphics audio
disabled
oneshot
writepid /dev/stune/top-app/tasks开机就启动进程，那肯定就要从rc里面找。负责开机动画的进程是bootanimation。上面是他的rc文件。值得注意的是，设置了disable标志位。
我们翻翻看在init进程,是怎么解析service的。在Android9.0中实际上会把service，action，import等都会进行字符串解析额，最后分散在三个链表等待执行。
文件：/system/core/init/service.cpp
const Service::OptionParserMap::Map& Service::OptionParserMap::map() const {
constexpr std::size_t kMax = std::numeric_limits<std::size_t>::max();
// clang-format off
static const Map option_parsers = {
{"capabilities",
{1, kMax, &Service::ParseCapabilities}},
{"class", {1, kMax, &Service::ParseClass}},
{"console", {0, 1, &Service::ParseConsole}},
{"critical", {0, 0, &Service::ParseCritical}},
{"disabled", {0, 0, &Service::ParseDisabled}},
{"enter_namespace",
{2, 2, &Service::ParseEnterNamespace}},
{"group", {1, NR_SVC_SUPP_GIDS + 1, &Service::ParseGroup}},
{"interface", {2, 2, &Service::ParseInterface}},
{"ioprio", {2, 2, &Service::ParseIoprio}},
{"priority", {1, 1, &Service::ParsePriority}},
{"keycodes", {1, kMax, &Service::ParseKeycodes}},
{"oneshot", {0, 0, &Service::ParseOneshot}},
{"onrestart", {1, kMax, &Service::ParseOnrestart}},
{"override", {0, 0, &Service::ParseOverride}},
{"oom_score_adjust",
{1, 1, &Service::ParseOomScoreAdjust}},
{"memcg.swappiness",
{1, 1, &Service::ParseMemcgSwappiness}},
{"memcg.soft_limit_in_bytes",
{1, 1, &Service::ParseMemcgSoftLimitInBytes}},
{"memcg.limit_in_bytes",
{1, 1, &Service::ParseMemcgLimitInBytes}},
{"namespace", {1, 2, &Service::ParseNamespace}},
{"rlimit", {3, 3, &Service::ParseProcessRlimit}},
{"seclabel", {1, 1, &Service::ParseSeclabel}},
{"setenv", {2, 2, &Service::ParseSetenv}},
{"shutdown", {1, 1, &Service::ParseShutdown}},
{"socket", {3, 6, &Service::ParseSocket}},
{"file", {2, 2, &Service::ParseFile}},
{"user", {1, 1, &Service::ParseUser}},
{"writepid", {1, kMax, &Service::ParseWritepid}},
};
// clang-format on
return option_parsers;
}在这个map中写好了每一个命令对应的解析方法指针。我们直接看看disable做了什么：
Result<Success> Service::ParseDisabled(const std::vector<std::string>& args) {
flags_ |= SVC_DISABLED;
flags_ |= SVC_RC_DISABLED;
return Success();
}很简单就是设置了DISABLED的flag。
当解析完毕将会尝试着执行解析好的service的命令。
Result<Success> Service::Start() {
bool disabled = (flags_ & (SVC_DISABLED | SVC_RESET));
flags_ &= (~(SVC_DISABLED|SVC_RESTARTING|SVC_RESET|SVC_RESTART|SVC_DISABLED_START));
if (flags_ & SVC_RUNNING) {
if ((flags_ & SVC_ONESHOT) && disabled) {
flags_ |= SVC_RESTART;
}
// It is not an error to try to start a service that is already running.
return Success();
}
bool needs_console = (flags_ & SVC_CONSOLE);
if (needs_console) {
if (console_.empty()) {
console_ = default_console;
}
int console_fd = open(console_.c_str(), O_RDWR | O_CLOEXEC);
if (console_fd < 0) {
flags_ |= SVC_DISABLED;
return ErrnoError() << "Couldn't open console '" << console_ << "'";
}
close(console_fd);
}
...
pid_t pid = -1;
if (namespace_flags_) {
pid = clone(nullptr, nullptr, namespace_flags_ | SIGCHLD, nullptr);
} else {
pid = fork();
}
if (pid == 0) {
...
}
if (pid < 0) {
pid_ = 0;
return ErrnoError() << "Failed to fork";
}
...
return Success();
}能看到如果没有disable，reset这些标志位阻碍，将会通过fork系统生成一个新的进程。但是这里disable了，因此不会走下来，而是会把解析结果保存起来。保存在ServiceList对象中的services_ vector集合。
到这里似乎逻辑断开了，我们先把思路阻塞到这里。稍后就能看到。
SF启动开机动画
在SF的init方法中，我为了独立出一节出来，故意有一段没有解析。如下：
文件：/frameworks/native/services/surfaceflinger/SurfaceFlinger.cpp
if (getHwComposer().hasCapability(
HWC2::Capability::PresentFenceIsNotReliable)) {
mStartPropertySetThread = new StartPropertySetThread(false);
} else {
mStartPropertySetThread = new StartPropertySetThread(true);
}
if (mStartPropertySetThread->Start() != NO_ERROR) {
ALOGE("Run StartPropertySetThread failed!");
}这个方法是干什么的呢？我第一次看的时候差点看漏了，差点找不到哪里启动开机动画，其实是把事情交给了StartPropertySetThread完成。
文件：/frameworks/native/services/surfaceflinger/StartPropertySetThread.cpp
StartPropertySetThread::StartPropertySetThread(bool timestampPropertyValue):
Thread(false), mTimestampPropertyValue(timestampPropertyValue) {}
status_t StartPropertySetThread::Start() {
return run("SurfaceFlinger::StartPropertySetThread", PRIORITY_NORMAL);
}
bool StartPropertySetThread::threadLoop() {
// Set property service.sf.present_timestamp, consumer need check its readiness
property_set(kTimestampProperty, mTimestampPropertyValue ? "1" : "0");
// Clear BootAnimation exit flag
property_set("service.bootanim.exit", "0");
// Start BootAnimation if not started
property_set("ctl.start", "bootanim");
// Exit immediately
return false;
}能看到在这里设置了两个系统属性，一个是service.bootanim.exit设置为0，另一个则是开机的关键，设置了ctl.start中的参数为bootanim。这样就能启动开机动画的进程。
为什么如此呢？我们还是要回到init进程的main函数中。
文件：/system/core/init/init.cpp
int main(int argc, char** argv) {
....
...
start_property_service();
...
const BuiltinFunctionMap function_map;
Action::set_function_map(&function_map);
subcontexts = InitializeSubcontexts();
ActionManager& am = ActionManager::GetInstance();
ServiceList& sm = ServiceList::GetInstance();
LoadBootScripts(am, sm);
// Turning this on and letting the INFO logging be discarded adds 0.2s to
// Nexus 9 boot time, so it's disabled by default.
if (false) DumpState();
am.QueueEventTrigger("early-init");
// Queue an action that waits for coldboot done so we know ueventd has set up all of /dev...
am.QueueBuiltinAction(wait_for_coldboot_done_action, "wait_for_coldboot_done");
// ... so that we can start queuing up actions that require stuff from /dev.
am.QueueBuiltinAction(MixHwrngIntoLinuxRngAction, "MixHwrngIntoLinuxRng");
am.QueueBuiltinAction(SetMmapRndBitsAction, "SetMmapRndBits");
am.QueueBuiltinAction(SetKptrRestrictAction, "SetKptrRestrict");
am.QueueBuiltinAction(keychord_init_action, "keychord_init");
am.QueueBuiltinAction(console_init_action, "console_init");
// Trigger all the boot actions to get us started.
am.QueueEventTrigger("init");
// Repeat mix_hwrng_into_linux_rng in case /dev/hw_random or /dev/random
// wasn't ready immediately after wait_for_coldboot_done
am.QueueBuiltinAction(MixHwrngIntoLinuxRngAction, "MixHwrngIntoLinuxRng");
// Don't mount filesystems or start core system services in charger mode.
std::string bootmode = GetProperty("ro.bootmode", "");
if (bootmode == "charger") {
am.QueueEventTrigger("charger");
} else {
am.QueueEventTrigger("late-init");
}
// Run all property triggers based on current state of the properties.
am.QueueBuiltinAction(queue_property_triggers_action, "queue_property_triggers");
...
return 0;
}我们忽律掉最下面init.cpp监听epoll消息的逻辑，其实在这个过程中还通过start_property_service启动了一个检测Android全局配置属性变化服务。
文件：http://androidxref.com/9.0.0_r3/xref/system/core/init/property_service.cpp
void start_property_service() {
selinux_callback cb;
cb.func_audit = SelinuxAuditCallback;
selinux_set_callback(SELINUX_CB_AUDIT, cb);
property_set("ro.property_service.version", "2");
property_set_fd = CreateSocket(PROP_SERVICE_NAME, SOCK_STREAM | SOCK_CLOEXEC | SOCK_NONBLOCK,
false, 0666, 0, 0, nullptr);
if (property_set_fd == -1) {
...
}
listen(property_set_fd, 8);
register_epoll_handler(property_set_fd, handle_property_set_fd);
}能看到在这个过程中，设置了版本号为2，启动了一个名字为property_service的socket服务。然后对这个服务进行监听，把property_set_fd注册到poll中，注册一个handle_property_set_fd回调事件。
我们先来看看property_set中做了什么事情：
文件：/bionic/libc/bionic/system_property_set.cpp
int __system_property_set(const char* key, const char* value) {
if (key == nullptr) return -1;
if (value == nullptr) value = "";
if (g_propservice_protocol_version == 0) {
detect_protocol_version();
}
if (g_propservice_protocol_version == kProtocolVersion1) {
....
} else {
if (strlen(value) >= PROP_VALUE_MAX && strncmp(key, "ro.", 3) != 0) return -1;
// Use proper protocol
PropertyServiceConnection connection;
if (!connection.IsValid()) {
errno = connection.GetLastError();
...
return -1;
}
SocketWriter writer(&connection);
if (!writer.WriteUint32(PROP_MSG_SETPROP2).WriteString(key).WriteString(value).Send()) {
errno = connection.GetLastError();
...
return -1;
}
int result = -1;
if (!connection.RecvInt32(&result)) {
errno = connection.GetLastError();
...
return -1;
}
...
return 0;
}
}因为版本号为2.其实它就会走下面的分之，此时能看到这不是简单的写入文件，而是写到了一个socket 中。
而这个socket是什么？
static const char property_service_socket[] = "/dev/socket/" PROP_SERVICE_NAME;
PropertyServiceConnection() : last_error_(0) {
socket_ = ::socket(AF_LOCAL, SOCK_STREAM | SOCK_CLOEXEC, 0);
if (socket_ == -1) {
last_error_ = errno;
return;
}
const size_t namelen = strlen(property_service_socket);
sockaddr_un addr;
memset(&addr, 0, sizeof(addr));
strlcpy(addr.sun_path, property_service_socket, sizeof(addr.sun_path));
addr.sun_family = AF_LOCAL;
socklen_t alen = namelen + offsetof(sockaddr_un, sun_path) + 1;
if (TEMP_FAILURE_RETRY(connect(socket_, reinterpret_cast<sockaddr*>(&addr), alen)) == -1) {
last_error_ = errno;
close(socket_);
socket_ = -1;
}
}我们能看到他的地址其实是dev/socket下的property_service。也就是刚好是上面注册的socket。
关键来看这个方法：
static void handle_property_set_fd() {
static constexpr uint32_t kDefaultSocketTimeout = 2000; /* ms */
int s = accept4(property_set_fd, nullptr, nullptr, SOCK_CLOEXEC);
if (s == -1) {
return;
}
ucred cr;
socklen_t cr_size = sizeof(cr);
if (getsockopt(s, SOL_SOCKET, SO_PEERCRED, &cr, &cr_size) < 0) {
close(s);
return;
}
SocketConnection socket(s, cr);
uint32_t timeout_ms = kDefaultSocketTimeout;
uint32_t cmd = 0;
if (!socket.RecvUint32(&cmd, &timeout_ms)) {
socket.SendUint32(PROP_ERROR_READ_CMD);
return;
}
switch (cmd) {
case PROP_MSG_SETPROP: {
...
}
case PROP_MSG_SETPROP2: {
std::string name;
std::string value;
if (!socket.RecvString(&name, &timeout_ms) ||
!socket.RecvString(&value, &timeout_ms)) {
socket.SendUint32(PROP_ERROR_READ_DATA);
return;
}
const auto& cr = socket.cred();
std::string error;
uint32_t result = HandlePropertySet(name, value, socket.source_context(), cr, &error);
if (result != PROP_SUCCESS) {
...
}
socket.SendUint32(result);
break;
}
default:
socket.SendUint32(PROP_ERROR_INVALID_CMD);
break;
}
}从上面得知，首先会写入PROP_MSG_SETPROP2一个命令，此时就会走到下面这个分之，接着通过RecvString读取数据内容，执行HandlePropertySet。
uint32_t HandlePropertySet(const std::string& name, const std::string& value,
const std::string& source_context, const ucred& cr, std::string* error) {
...
if (StartsWith(name, "ctl.")) {
if (!CheckControlPropertyPerms(name, value, source_context, cr)) {
*error = StringPrintf("Invalid permissions to perform '%s' on '%s'", name.c_str() + 4,
value.c_str());
return PROP_ERROR_HANDLE_CONTROL_MESSAGE;
}
HandleControlMessage(name.c_str() + 4, value, cr.pid);
return PROP_SUCCESS;
}
...
return PropertySet(name, value, error);
}
在SF中输送了两个属性过来，其中使用HandleControlMessage对ctl.进行了特殊处理。
static const std::map<std::string, ControlMessageFunction>& get_control_message_map() {
// clang-format off
static const std::map<std::string, ControlMessageFunction> control_message_functions = {
{"start", {ControlTarget::SERVICE, DoControlStart}},
{"stop", {ControlTarget::SERVICE, DoControlStop}},
{"restart", {ControlTarget::SERVICE, DoControlRestart}},
{"interface_start", {ControlTarget::INTERFACE, DoControlStart}},
{"interface_stop", {ControlTarget::INTERFACE, DoControlStop}},
{"interface_restart", {ControlTarget::INTERFACE, DoControlRestart}},
};
// clang-format on
return control_message_functions;
}
static Result<Success> DoControlStart(Service* service) {
return service->Start();
}
void HandleControlMessage(const std::string& msg, const std::string& name, pid_t pid) {
const auto& map = get_control_message_map();
const auto it = map.find(msg);
if (it == map.end()) {
...
return;
}
std::string cmdline_path = StringPrintf("proc/%d/cmdline", pid);
std::string process_cmdline;
if (ReadFileToString(cmdline_path, &process_cmdline)) {
std::replace(process_cmdline.begin(), process_cmdline.end(), '\0', ' ');
process_cmdline = Trim(process_cmdline);
} else {
process_cmdline = "unknown process";
}
...
const ControlMessageFunction& function = it->second;
if (function.target == ControlTarget::SERVICE) {
Service* svc = ServiceList::GetInstance().FindService(name);
if (svc == nullptr) {
...
return;
}
if (auto result = function.action(svc); !result) {
...
}
return;
}
....
}这里面的逻辑十分简单，本质上就是继续获取从property_set传递过来后续的字符串。也就是ctl.xxx点后面的命令对应的方法。并且先通过serviceList找到解析好的服务，调用缓存在map中命令start对应的方法指针，也就是service的start。就重新走到上面Service::Start fork出进程的逻辑中。
BootAnimation进程启动
int main()
{
setpriority(PRIO_PROCESS, 0, ANDROID_PRIORITY_DISPLAY);
bool noBootAnimation = bootAnimationDisabled();
ALOGI_IF(noBootAnimation, "boot animation disabled");
if (!noBootAnimation) {
sp<ProcessState> proc(ProcessState::self());
ProcessState::self()->startThreadPool();
waitForSurfaceFlinger();
// create the boot animation object
sp<BootAnimation> boot = new BootAnimation(new AudioAnimationCallbacks());
ALOGV("Boot animation set up. Joining pool.");
IPCThreadState::self()->joinThreadPool();
}
ALOGV("Boot animation exit");
return 0;
}首先默认当前noBootAnimation是false。因此会初始化Binder的驱动，调用waitForSurfaceFlinger从serviceManager中查找SF进程，找到才生成一个BootAnimation对象准备执行开机动画，并设置了一个音轨的回调。
BootAnimation 初始化
接下来就会揭开本片文章的秘密，为什么没有Activity还是能够显示界面。其核心原理是什么。
文件：/frameworks/base/cmds/bootanimation/BootAnimation.cpp
BootAnimation::BootAnimation(sp<Callbacks> callbacks)
: Thread(false), mClockEnabled(true), mTimeIsAccurate(false),
mTimeFormat12Hour(false), mTimeCheckThread(NULL), mCallbacks(callbacks) {
mSession = new SurfaceComposerClient();
...
}在这个构造函数中，生成了一个十分重要的对象SurfaceComposerClient。因为SurfaceComposerClient是一个sp强智能指针，会继续走到onFirstRef中。
void SurfaceComposerClient::onFirstRef() {
sp<ISurfaceComposer> sf(ComposerService::getComposerService());
if (sf != 0 && mStatus == NO_INIT) {
auto rootProducer = mParent.promote();
sp<ISurfaceComposerClient> conn;
conn = (rootProducer != nullptr) ? sf->createScopedConnection(rootProducer) :
sf->createConnection();
if (conn != 0) {
mClient = conn;
mStatus = NO_ERROR;
}
}
}先拿到一个单例的ComposerService 服务对象，接着通过ISurfaceComposer通过createScopedConnection通信创建一个ISurfaceComposerClient。
ISurfaceComposer指代的是什么，ISurfaceComposerClient又是指什么呢？
ComposerService的初始化
/*static*/ sp<ISurfaceComposer> ComposerService::getComposerService() {
ComposerService& instance = ComposerService::getInstance();
Mutex::Autolock _l(instance.mLock);
if (instance.mComposerService == NULL) {
ComposerService::getInstance().connectLocked();
assert(instance.mComposerService != NULL);
ALOGD("ComposerService reconnected");
}
return instance.mComposerService;
}
能看到它实际上是一个单例设计,返回了ISurfaceComposer对象。
ComposerService::ComposerService()
: Singleton<ComposerService>() {
Mutex::Autolock _l(mLock);
connectLocked();
}
void ComposerService::connectLocked() {
const String16 name("SurfaceFlinger");
while (getService(name, &mComposerService) != NO_ERROR) {
usleep(250000);
}
assert(mComposerService != NULL);
// Create the death listener.
class DeathObserver : public IBinder::DeathRecipient {
ComposerService& mComposerService;
virtual void binderDied(const wp<IBinder>& who) {
ALOGW("ComposerService remote (surfaceflinger) died [%p]",
who.unsafe_get());
mComposerService.composerServiceDied();
}
public:
explicit DeathObserver(ComposerService& mgr) : mComposerService(mgr) { }
};
mDeathObserver = new DeathObserver(*const_cast<ComposerService*>(this));
IInterface::asBinder(mComposerService)->linkToDeath(mDeathObserver);
}能看到在这个过程中，会从ServiceManager查找SF在Binder驱动中映射的服务。并且绑定上另一个死亡代理，用于销毁ComposerService中的资源。
到此时SF的binder接口已经对着BootAnimation暴露了。
了解ISurfaceComposer 本质上就是SF的远程端口，接下来再看看ISurfaceComposerClient是什么。
ISurfaceComposer createConnection
实际调用的是SF的createConnection
文件：/frameworks/native/services/surfaceflinger/SurfaceFlinger.cpp
sp<ISurfaceComposerClient> SurfaceFlinger::createConnection() {
return initClient(new Client(this));
}文件：/frameworks/native/services/surfaceflinger/Client.cpp
class Client : public BnSurfaceComposerClientClient::Client(const sp<SurfaceFlinger>& flinger)
: Client(flinger, nullptr)
{
}本质上就是一个实现了BnSurfaceComposerClient的Client对象。之后关于渲染的对象将会从中生成。
BootAnimation onFirstRef
void BootAnimation::onFirstRef() {
status_t err = mSession->linkToComposerDeath(this);
ALOGE_IF(err, "linkToComposerDeath failed (%s) ", strerror(-err));
if (err == NO_ERROR) {
run("BootAnimation", PRIORITY_DISPLAY);
}
}当通过SurfaceComposerClient链接到远程Binder服务后，就会执行run方法。
文件：/frameworks/native/libs/gui/SurfaceComposerClient.cpp
status_t SurfaceComposerClient::linkToComposerDeath(
const sp<IBinder::DeathRecipient>& recipient,
void* cookie, uint32_t flags) {
sp<ISurfaceComposer> sf(ComposerService::getComposerService());
return IInterface::asBinder(sf)->linkToDeath(recipient, cookie, flags);
}能看到本质上是生成一个ComposerService BpBinder对象，并且进行Binder的死亡代理绑定。
BootAnimation run
本质上BootAnimation还是一个线程：
class BootAnimation : public Thread, public IBinder::DeathRecipient因此执行run之后，会先执行readyToRun，接着执行treadLoop方法。注意这两个方法都已经在线程中了。
BootAnimation readyToRun 准备渲染流程
status_t BootAnimation::readyToRun() {
mAssets.addDefaultAssets();
sp<IBinder> dtoken(SurfaceComposerClient::getBuiltInDisplay(
ISurfaceComposer::eDisplayIdMain));
DisplayInfo dinfo;
status_t status = SurfaceComposerClient::getDisplayInfo(dtoken, &dinfo);
if (status)
return -1;
// create the native surface
sp<SurfaceControl> control = session()->createSurface(String8("BootAnimation"),
dinfo.w, dinfo.h, PIXEL_FORMAT_RGB_565);
SurfaceComposerClient::Transaction t;
t.setLayer(control, 0x40000000)
.apply();
sp<Surface> s = control->getSurface();
// initialize opengl and egl
const EGLint attribs[] = {
EGL_RED_SIZE, 8,
EGL_GREEN_SIZE, 8,
EGL_BLUE_SIZE, 8,
EGL_DEPTH_SIZE, 0,
EGL_NONE
};
EGLint w, h;
EGLint numConfigs;
EGLConfig config;
EGLSurface surface;
EGLContext context;
EGLDisplay display = eglGetDisplay(EGL_DEFAULT_DISPLAY);
eglInitialize(display, 0, 0);
eglChooseConfig(display, attribs, &config, 1, &numConfigs);
surface = eglCreateWindowSurface(display, config, s.get(), NULL);
context = eglCreateContext(display, config, NULL, NULL);
eglQuerySurface(display, surface, EGL_WIDTH, &w);
eglQuerySurface(display, surface, EGL_HEIGHT, &h);
if (eglMakeCurrent(display, surface, surface, context) == EGL_FALSE)
return NO_INIT;
mDisplay = display;
mContext = context;
mSurface = surface;
mWidth = w;
mHeight = h;
mFlingerSurfaceControl = control;
mFlingerSurface = s;
// If the device has encryption turned on or is in process
// of being encrypted we show the encrypted boot animation.
char decrypt[PROPERTY_VALUE_MAX];
property_get("vold.decrypt", decrypt, "");
bool encryptedAnimation = atoi(decrypt) != 0 ||
!strcmp("trigger_restart_min_framework", decrypt);
if (!mShuttingDown && encryptedAnimation) {
static const char* encryptedBootFiles[] =
{PRODUCT_ENCRYPTED_BOOTANIMATION_FILE, SYSTEM_ENCRYPTED_BOOTANIMATION_FILE};
for (const char* f : encryptedBootFiles) {
if (access(f, R_OK) == 0) {
mZipFileName = f;
return NO_ERROR;
}
}
}
static const char* bootFiles[] =
{PRODUCT_BOOTANIMATION_FILE, OEM_BOOTANIMATION_FILE, SYSTEM_BOOTANIMATION_FILE};
static const char* shutdownFiles[] =
{PRODUCT_SHUTDOWNANIMATION_FILE, OEM_SHUTDOWNANIMATION_FILE, SYSTEM_SHUTDOWNANIMATION_FILE};
for (const char* f : (!mShuttingDown ? bootFiles : shutdownFiles)) {
if (access(f, R_OK) == 0) {
mZipFileName = f;
return NO_ERROR;
}
}
return NO_ERROR;
}在准备渲染流程中，做的事情有如下几个步骤：
- 1.SurfaceComposerClient::getBuiltInDisplay 从SF中查询可用的物理屏幕
- 2.SurfaceComposerClient::getDisplayInfo 从SF中获取屏幕的详细信息
- 3.session()->createSurface 通过Client创建绘制平面控制中心
- 4.t.setLayer(control, 0x40000000) 设置当前layer的层级
- 5.control->getSurface 获取真正的绘制平面对象
- 6.eglGetDisplay 获取opengl es的默认主屏幕，加载OpenGL es
- 7.eglInitialize 初始化屏幕对象和着色器缓存
- 8.eglChooseConfig 自动筛选出最合适的配置
- 9.eglCreateWindowSurface 从Surface中创建一个opengl es的surface
- 10.eglCreateContext 创建当前opengl es 的上下文
- 11.eglQuerySurface 查找当前环境的宽高属性
- 12.eglMakeCurrent 把上下文Context，屏幕display还有渲染面surface,线程关联起来。
- 13.从如下几个目录查找zip文件，分为两种模式，一种是加密文件的动画，一种是普通压缩文件动画：
在这些zip包中其实就是一张张图片。播放的时候，解压这些zip包，一张张的图片想动画一样播出。static const char OEM_BOOTANIMATION_FILE[] = "/oem/media/bootanimation.zip"; static const char PRODUCT_BOOTANIMATION_FILE[] = "/product/media/bootanimation.zip"; static const char SYSTEM_BOOTANIMATION_FILE[] = "/system/media/bootanimation.zip"; static const char PRODUCT_ENCRYPTED_BOOTANIMATION_FILE[] = "/product/media/bootanimation-encrypted.zip"; static const char SYSTEM_ENCRYPTED_BOOTANIMATION_FILE[] = "/system/media/bootanimation-encrypted.zip"; static const char OEM_SHUTDOWNANIMATION_FILE[] = "/oem/media/shutdownanimation.zip"; static const char PRODUCT_SHUTDOWNANIMATION_FILE[] = "/product/media/shutdownanimation.zip"; static const char SYSTEM_SHUTDOWNANIMATION_FILE[] = "/system/media/shutdownanimation.zip";
从第6点开始就是opengl es开发初四话流程的套路。其实真的核心的准备核心还是前5点。opengles的环境真正和Android系统关联起来是是第9点创建opengles的surface时候和Android的本地窗口互相绑定。
BootAnimation threadLoop
bool BootAnimation::threadLoop()
{
bool r;
// We have no bootanimation file, so we use the stock android logo
// animation.
if (mZipFileName.isEmpty()) {
r = android();
} else {
r = movie();
}
eglMakeCurrent(mDisplay, EGL_NO_SURFACE, EGL_NO_SURFACE, EGL_NO_CONTEXT);
eglDestroyContext(mDisplay, mContext);
eglDestroySurface(mDisplay, mSurface);
mFlingerSurface.clear();
mFlingerSurfaceControl.clear();
eglTerminate(mDisplay);
eglReleaseThread();
IPCThreadState::self()->stopProcess();
return r;
}在这里如果设定了bootanimation的zip压缩包则会走movie解压播放zip中的动画，否则就会走android默认动画。
BootAnimation moive
既然老罗解析了Android默认的动画，我就去解析Android自定义动画的核心原理。
bool BootAnimation::movie()
{
Animation* animation = loadAnimation(mZipFileName);
if (animation == NULL)
return false;
...
mUseNpotTextures = false;
String8 gl_extensions;
const char* exts = reinterpret_cast<const char*>(glGetString(GL_EXTENSIONS));
if (!exts) {
glGetError();
} else {
gl_extensions.setTo(exts);
if ((gl_extensions.find("GL_ARB_texture_non_power_of_two") != -1) ||
(gl_extensions.find("GL_OES_texture_npot") != -1)) {
mUseNpotTextures = true;
}
}
// Blend required to draw time on top of animation frames.
//设置混合颜色模式 后面是1 - 原图的四个颜色分量
glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
//设置颜色过度模式，非平滑模式
glShadeModel(GL_FLAT);
glDisable(GL_DITHER);
glDisable(GL_SCISSOR_TEST);
glDisable(GL_BLEND);
//绑定纹理
glBindTexture(GL_TEXTURE_2D, 0);
//启动纹理
glEnable(GL_TEXTURE_2D);
//控制纹理如何与片元颜色进行计算的 设置纹理环境，纹理代替片元
glTexEnvx(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_REPLACE);
//设置横纵两轴的边界外以重复模式绘制纹理
glTexParameterx(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);
glTexParameterx(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);
//为线性过滤
glTexParameterx(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
glTexParameterx(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
bool clockFontInitialized = false;
if (mClockEnabled) {
clockFontInitialized =
(initFont(&animation->clockFont, CLOCK_FONT_ASSET) == NO_ERROR);
mClockEnabled = clockFontInitialized;
}
if (mClockEnabled && !updateIsTimeAccurate()) {
mTimeCheckThread = new TimeCheckThread(this);
mTimeCheckThread->run("BootAnimation::TimeCheckThread", PRIORITY_NORMAL);
}
playAnimation(*animation);
if (mTimeCheckThread != nullptr) {
mTimeCheckThread->requestExit();
mTimeCheckThread = nullptr;
}
releaseAnimation(animation);
if (clockFontInitialized) {
glDeleteTextures(1, &animation->clockFont.texture.name);
}
return false;
}大致分为三步骤：
- 1.loadAnimation 解析zip包的动画数据
- 2.初始化纹理设置
- 3.playAnimation 播放解析好的纹理数据
- 4.releaseAnimation 播放完毕释放资源
loadAnimation
BootAnimation::Animation* BootAnimation::loadAnimation(const String8& fn)
{
if (mLoadedFiles.indexOf(fn) >= 0) {
ALOGE("File \"%s\" is already loaded. Cyclic ref is not allowed",
fn.string());
return NULL;
}
ZipFileRO *zip = ZipFileRO::open(fn);
if (zip == NULL) {
ALOGE("Failed to open animation zip \"%s\": %s",
fn.string(), strerror(errno));
return NULL;
}
Animation *animation = new Animation;
animation->fileName = fn;
animation->zip = zip;
animation->clockFont.map = nullptr;
mLoadedFiles.add(animation->fileName);
parseAnimationDesc(*animation);
if (!preloadZip(*animation)) {
return NULL;
}
mLoadedFiles.remove(fn);
return animation;
}
关键方法有两个，第一个是parseAnimationDesc，第二个是preloadZip。
parseAnimationDesc 解析zip包中的描述文件
bool BootAnimation::parseAnimationDesc(Animation& animation)
{
String8 desString;
if (!readFile(animation.zip, "desc.txt", desString)) {
return false;
}
char const* s = desString.string();
// Parse the description file
for (;;) {
const char* endl = strstr(s, "\n");
if (endl == NULL) break;
String8 line(s, endl - s);
const char* l = line.string();
int fps = 0;
int width = 0;
int height = 0;
int count = 0;
int pause = 0;
char path[ANIM_ENTRY_NAME_MAX];
char color[7] = "000000"; // default to black if unspecified
char clockPos1[TEXT_POS_LEN_MAX + 1] = "";
char clockPos2[TEXT_POS_LEN_MAX + 1] = "";
char pathType;
if (sscanf(l, "%d %d %d", &width, &height, &fps) == 3) {
// ALOGD("> w=%d, h=%d, fps=%d", width, height, fps);
animation.width = width;
animation.height = height;
animation.fps = fps;
} else if (sscanf(l, " %c %d %d %s #%6s %16s %16s",
&pathType, &count, &pause, path, color, clockPos1, clockPos2) >= 4) {
//ALOGD("> type=%c, count=%d, pause=%d, path=%s, color=%s, clockPos1=%s, clockPos2=%s",
// pathType, count, pause, path, color, clockPos1, clockPos2);
Animation::Part part;
part.playUntilComplete = pathType == 'c';
part.count = count;
part.pause = pause;
part.path = path;
part.audioData = NULL;
part.animation = NULL;
if (!parseColor(color, part.backgroundColor)) {
ALOGE("> invalid color '#%s'", color);
part.backgroundColor[0] = 0.0f;
part.backgroundColor[1] = 0.0f;
part.backgroundColor[2] = 0.0f;
}
parsePosition(clockPos1, clockPos2, &part.clockPosX, &part.clockPosY);
animation.parts.add(part);
}
else if (strcmp(l, "$SYSTEM") == 0) {
// ALOGD("> SYSTEM");
Animation::Part part;
part.playUntilComplete = false;
part.count = 1;
part.pause = 0;
part.audioData = NULL;
part.animation = loadAnimation(String8(SYSTEM_BOOTANIMATION_FILE));
if (part.animation != NULL)
animation.parts.add(part);
}
s = ++endl;
}
return true;
}想要正常解析开机动画，需要有一个desc.txt。有一个例子如下：
241 63 60
c 1 30 part0
c 1 0 part1
c 0 0 part2
c 1 64 part3
c 1 15 part4该文件头三个字符串定义了宽高，和帧数。找到\n结束后就到下一行中去。
接下来的部分就是动画每一部分，第一个字符串c是指是否一直播放到结束；第而个则是指pause，是暂停的帧数；第三个int是指当前帧数中有加载目录下多少画面，最后一个代表资源路径。
把每一部分当成一个part保存在Animation中。
当然在Android 9.0版本中还能设置更多的选项如音频等。
preloadZip预加载zip
bool BootAnimation::preloadZip(Animation& animation)
{
// read all the data structures
const size_t pcount = animation.parts.size();
void *cookie = NULL;
ZipFileRO* zip = animation.zip;
if (!zip->startIteration(&cookie)) {
return false;
}
ZipEntryRO entry;
char name[ANIM_ENTRY_NAME_MAX];
while ((entry = zip->nextEntry(cookie)) != NULL) {
const int foundEntryName = zip->getEntryFileName(entry, name, ANIM_ENTRY_NAME_MAX);
if (foundEntryName > ANIM_ENTRY_NAME_MAX || foundEntryName == -1) {
continue;
}
const String8 entryName(name);
const String8 path(entryName.getPathDir());
const String8 leaf(entryName.getPathLeaf());
if (leaf.size() > 0) {
if (entryName == CLOCK_FONT_ZIP_NAME) {
FileMap* map = zip->createEntryFileMap(entry);
if (map) {
animation.clockFont.map = map;
}
continue;
}
for (size_t j = 0; j < pcount; j++) {
if (path == animation.parts[j].path) {
uint16_t method;
// supports only stored png files
if (zip->getEntryInfo(entry, &method, NULL, NULL, NULL, NULL, NULL)) {
if (method == ZipFileRO::kCompressStored) {
FileMap* map = zip->createEntryFileMap(entry);
if (map) {
Animation::Part& part(animation.parts.editItemAt(j));
if (leaf == "audio.wav") {
// a part may have at most one audio file
part.audioData = (uint8_t *)map->getDataPtr();
part.audioLength = map->getDataLength();
} else if (leaf == "trim.txt") {
part.trimData.setTo((char const*)map->getDataPtr(),
map->getDataLength());
} else {
Animation::Frame frame;
frame.name = leaf;
frame.map = map;
frame.trimWidth = animation.width;
frame.trimHeight = animation.height;
frame.trimX = 0;
frame.trimY = 0;
part.frames.add(frame);
}
}
} else {
...
}
}
}
}
}
}
for (Animation::Part& part : animation.parts) {
const char* trimDataStr = part.trimData.string();
for (size_t frameIdx = 0; frameIdx < part.frames.size(); frameIdx++) {
const char* endl = strstr(trimDataStr, "\n");
// No more trimData for this part.
if (endl == NULL) {
break;
}
String8 line(trimDataStr, endl - trimDataStr);
const char* lineStr = line.string();
trimDataStr = ++endl;
int width = 0, height = 0, x = 0, y = 0;
if (sscanf(lineStr, "%dx%d+%d+%d", &width, &height, &x, &y) == 4) {
Animation::Frame& frame(part.frames.editItemAt(frameIdx));
frame.trimWidth = width;
frame.trimHeight = height;
frame.trimX = x;
frame.trimY = y;
} else {
break;
}
}
}
mCallbacks->init(animation.parts);
zip->endIteration(cookie);
return true;
}这里面做了两件事情：
- 1.首先，解压zip包中所有的资源，注入到每一个Animation parts中。让其拥有真正的资源地址。
- 2.根据每一个parts中的资源数据和头信息，生成一个个Frame保存在Animation中。
playAnimation 播放动画
bool BootAnimation::playAnimation(const Animation& animation)
{
const size_t pcount = animation.parts.size();
nsecs_t frameDuration = s2ns(1) / animation.fps;
const int animationX = (mWidth - animation.width) / 2;
const int animationY = (mHeight - animation.height) / 2;
ALOGD("%sAnimationShownTiming start time: %" PRId64 "ms", mShuttingDown ? "Shutdown" : "Boot",
elapsedRealtime());
for (size_t i=0 ; i<pcount ; i++) {
const Animation::Part& part(animation.parts[i]);
const size_t fcount = part.frames.size();
glBindTexture(GL_TEXTURE_2D, 0);
// Handle animation package
if (part.animation != NULL) {
playAnimation(*part.animation);
if (exitPending())
break;
continue; //to next part
}
for (int r=0 ; !part.count || r<part.count ; r++) {
// Exit any non playuntil complete parts immediately
if(exitPending() && !part.playUntilComplete)
break;
mCallbacks->playPart(i, part, r);
glClearColor(
part.backgroundColor[0],
part.backgroundColor[1],
part.backgroundColor[2],
1.0f);
for (size_t j=0 ; j<fcount && (!exitPending() || part.playUntilComplete) ; j++) {
const Animation::Frame& frame(part.frames[j]);
nsecs_t lastFrame = systemTime();
if (r > 0) {
glBindTexture(GL_TEXTURE_2D, frame.tid);
} else {
if (part.count != 1) {
glGenTextures(1, &frame.tid);
glBindTexture(GL_TEXTURE_2D, frame.tid);
glTexParameterx(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
glTexParameterx(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
}
int w, h;
initTexture(frame.map, &w, &h);
}
const int xc = animationX + frame.trimX;
const int yc = animationY + frame.trimY;
Region clearReg(Rect(mWidth, mHeight));
clearReg.subtractSelf(Rect(xc, yc, xc+frame.trimWidth, yc+frame.trimHeight));
if (!clearReg.isEmpty()) {
Region::const_iterator head(clearReg.begin());
Region::const_iterator tail(clearReg.end());
glEnable(GL_SCISSOR_TEST);
while (head != tail) {
const Rect& r2(*head++);
glScissor(r2.left, mHeight - r2.bottom, r2.width(), r2.height());
glClear(GL_COLOR_BUFFER_BIT);
}
glDisable(GL_SCISSOR_TEST);
}
glDrawTexiOES(xc, mHeight - (yc + frame.trimHeight),
0, frame.trimWidth, frame.trimHeight);
if (mClockEnabled && mTimeIsAccurate && validClock(part)) {
drawClock(animation.clockFont, part.clockPosX, part.clockPosY);
}
eglSwapBuffers(mDisplay, mSurface);
nsecs_t now = systemTime();
nsecs_t delay = frameDuration - (now - lastFrame);
//ALOGD("%lld, %lld", ns2ms(now - lastFrame), ns2ms(delay));
lastFrame = now;
if (delay > 0) {
struct timespec spec;
spec.tv_sec = (now + delay) / 1000000000;
spec.tv_nsec = (now + delay) % 1000000000;
int err;
do {
err = clock_nanosleep(CLOCK_MONOTONIC, TIMER_ABSTIME, &spec, NULL);
} while (err<0 && errno == EINTR);
}
checkExit();
}
usleep(part.pause * ns2us(frameDuration));
// For infinite parts, we've now played them at least once, so perhaps exit
if(exitPending() && !part.count)
break;
}
}
// Free textures created for looping parts now that the animation is done.
for (const Animation::Part& part : animation.parts) {
if (part.count != 1) {
const size_t fcount = part.frames.size();
for (size_t j = 0; j < fcount; j++) {
const Animation::Frame& frame(part.frames[j]);
glDeleteTextures(1, &frame.tid);
}
}
}
return true;
}能看到在这个过程中，如果没有设置c标志为则不会播放。否则将会循环每一个每一个part中对应frame的个数。当是frame的第一帧的时候将会初始化纹理，设置好纹理需要加载的数据以及宽高，并且绑定当前frame的id为渲染纹理的句柄。
找到动画的动画的启动位置，其位置就是整个屏幕的宽高-动画绘制区域宽高的1/2，保证整个动画刚好在大小适应的位置。
获取到区域之后，通过glScissor进行裁剪。glDrawTexiOES绘制纹理位置，最后进行opengles 缓冲区交换。计算当前已经消耗的时间和每一帧进行比对，再进行延时处理。
最后处理pause的数据，查看需要暂停沉睡多少帧。
最后的最后，销毁每一个绑定在frame.id上的纹理。以及调用checkExit检测是否需要退出该进程。
releaseAnimation
void BootAnimation::releaseAnimation(Animation* animation) const
{
for (Vector<Animation::Part>::iterator it = animation->parts.begin(),
e = animation->parts.end(); it != e; ++it) {
if (it->animation)
releaseAnimation(it->animation);
}
if (animation->zip)
delete animation->zip;
delete animation;
}销毁animation中part以及zip映射的内存。
那么什么时候才是整个进程真正销毁呢？那一般就是桌面进程准备显示了，那就应该销毁BootAnimation进程了。我们可以猜测就在桌面的Activity 进入了Resume之后进行销毁的。
BootAnimation 进程的销毁
文件：/frameworks/base/core/java/android/app/ActivityThread.java
public void handleResumeActivity(IBinder token, boolean finalStateRequest, boolean isForward,
String reason) {
...
Looper.myQueue().addIdleHandler(new Idler());
}在执行完Resume之后，会添加一次IdleHandler对象。让进程空闲执行。
public final boolean queueIdle() {
ActivityClientRecord a = mNewActivities;
boolean stopProfiling = false;
...
if (a != null) {
mNewActivities = null;
IActivityManager am = ActivityManager.getService();
ActivityClientRecord prev;
do {
if (a.activity != null && !a.activity.mFinished) {
try {
am.activityIdle(a.token, a.createdConfig, stopProfiling);
a.createdConfig = null;
} catch (RemoteException ex) {
throw ex.rethrowFromSystemServer();
}
}
prev = a;
a = a.nextIdle;
prev.nextIdle = null;
} while (a != null);
}
...
return false;
}该方法将会通信到AMS中。
文件：/frameworks/base/services/core/java/com/android/server/am/ActivityManagerService.java
@Override
public final void activityIdle(IBinder token, Configuration config, boolean stopProfiling) {
final long origId = Binder.clearCallingIdentity();
synchronized (this) {
ActivityStack stack = ActivityRecord.getStackLocked(token);
if (stack != null) {
ActivityRecord r =
mStackSupervisor.activityIdleInternalLocked(token, false /* fromTimeout */,
false /* processPausingActivities */, config);
if (stopProfiling) {
if ((mProfileProc == r.app) && mProfilerInfo != null) {
clearProfilerLocked();
}
}
}
}
Binder.restoreCallingIdentity(origId);
}文件：/frameworks/base/services/core/java/com/android/server/am/ActivityStackSupervisor.java
final ActivityRecord activityIdleInternalLocked(final IBinder token, boolean fromTimeout,
boolean processPausingActivities, Configuration config) {
if (DEBUG_ALL) Slog.v(TAG, "Activity idle: " + token);
ArrayList<ActivityRecord> finishes = null;
ArrayList<UserState> startingUsers = null;
int NS = 0;
int NF = 0;
boolean booting = false;
boolean activityRemoved = false;
ActivityRecord r = ActivityRecord.forTokenLocked(token);
if (r != null) {
....
mHandler.removeMessages(IDLE_TIMEOUT_MSG, r);
r.finishLaunchTickingLocked();
if (fromTimeout) {
reportActivityLaunchedLocked(fromTimeout, r, -1, -1);
}
if (config != null) {
r.setLastReportedGlobalConfiguration(config);
}
// We are now idle. If someone is waiting for a thumbnail from
// us, we can now deliver.
r.idle = true;
if (isFocusedStack(r.getStack()) || fromTimeout) {
booting = checkFinishBootingLocked();
}
}
....
}
....
return r;
}能看到此时将会执行checkFinishBootingLocked检测BootAnimation是否关闭。
private boolean checkFinishBootingLocked() {
final boolean booting = mService.mBooting;
boolean enableScreen = false;
mService.mBooting = false;
if (!mService.mBooted) {
mService.mBooted = true;
enableScreen = true;
}
if (booting || enableScreen) {
mService.postFinishBooting(booting, enableScreen);
}
return booting;
}这里很简单，就是一个全局的标志位判断,接下来就回到AMS中
void postFinishBooting(boolean finishBooting, boolean enableScreen) {
mHandler.sendMessage(mHandler.obtainMessage(FINISH_BOOTING_MSG,
finishBooting ? 1 : 0, enableScreen ? 1 : 0));
}进入AMS的Handler中
case FINISH_BOOTING_MSG: {
if (msg.arg1 != 0) {
finishBooting();
}
if (msg.arg2 != 0) {
enableScreenAfterBoot();
}
break;
}会执行finishBooting继续设置一个标志位。这个标志用来判断不需要其他时候有其他进程来执行结束BootAnimation进程的操作。
void enableScreenAfterBoot() {
mWindowManager.enableScreenAfterBoot();
...
}此时就会走到WMS中的enableScreenAfterBoot。因为WMS作为窗体管理服务，肯定有渲染相关的服务在里面。
文件：/frameworks/base/services/core/java/com/android/server/wm/WindowManagerService.java
public void enableScreenAfterBoot() {
synchronized(mWindowMap) {
...
if (mSystemBooted) {
return;
}
mSystemBooted = true;
hideBootMessagesLocked();
mH.sendEmptyMessageDelayed(H.BOOT_TIMEOUT, 30 * 1000);
}
mPolicy.systemBooted();
performEnableScreen();
} private void performEnableScreen() {
synchronized(mWindowMap) {
...
try {
IBinder surfaceFlinger = ServiceManager.getService("SurfaceFlinger");
if (surfaceFlinger != null) {
Parcel data = Parcel.obtain();
data.writeInterfaceToken("android.ui.ISurfaceComposer");
surfaceFlinger.transact(IBinder.FIRST_CALL_TRANSACTION, // BOOT_FINISHED
data, null, 0);
data.recycle();
}
} catch (RemoteException ex) {
...
}
...
try {
mActivityManager.bootAnimationComplete();
} catch (RemoteException e) {
}
...
}关键是通信到SF中，传入了FIRST_CALL_TRANSACTION命令，而这个命令实际上就是BOOT_FINISHED。
BOOT_FINISHED = IBinder::FIRST_CALL_TRANSACTION,我们去SF的基类看看做了什么。
文件：/frameworks/native/libs/gui/ISurfaceComposer.cpp
case BOOT_FINISHED: {
CHECK_INTERFACE(ISurfaceComposer, data, reply);
bootFinished();
return NO_ERROR;
}其实就是SF中的bootFinished方法。
void SurfaceFlinger::bootFinished()
{
if (mStartPropertySetThread->join() != NO_ERROR) {
ALOGE("Join StartPropertySetThread failed!");
}
const nsecs_t now = systemTime();
const nsecs_t duration = now - mBootTime;
ALOGI("Boot is finished (%ld ms)", long(ns2ms(duration)) );
// wait patiently for the window manager death
const String16 name("window");
sp<IBinder> window(defaultServiceManager()->getService(name));
if (window != 0) {
window->linkToDeath(static_cast<IBinder::DeathRecipient*>(this));
}
....
property_set("service.bootanim.exit", "1");
const int LOGTAG_SF_STOP_BOOTANIM = 60110;
LOG_EVENT_LONG(LOGTAG_SF_STOP_BOOTANIM,
ns2ms(systemTime(SYSTEM_TIME_MONOTONIC)));
sp<LambdaMessage> readProperties = new LambdaMessage([&]() {
readPersistentProperties();
});
postMessageAsync(readProperties);
}在此刻，SF绑定了对WMS的Binder死亡代理。不过关键还是设置了service.bootanim.exit这个全局属性。而这个属性刚好就是BootAnimation在checkExit方法中不断循环检测。
void BootAnimation::checkExit() {
// Allow surface flinger to gracefully request shutdown
char value[PROPERTY_VALUE_MAX];
property_get(EXIT_PROP_NAME, value, "0");
int exitnow = atoi(value);
if (exitnow) {
requestExit();
mCallbacks->shutdown();
}
}requestExit其实就是退出该BootAnimation线程的threadLoop方法，这样整个main方法就不会阻塞住，就会一直运行整个main到底结束整个进程。
总结
用一幅图总结：
这些其实都是普通的OpenGL es的操作。但是似乎把Android渲染系统部分给屏蔽掉了。我们似乎没有办法继续探索下去了？不得不说封装的太棒了，压根没有感受到OpenGL es适配了平台的特性。
回答开头的疑问，为什么我们不需要Activity也能渲染呢，由始至终都没有看到Activity的存在？其实Activity本身并不是负责渲染，它不过是集UI交互的大成者。真正负责渲染的，其实是由Surface联通SF进行交互渲染的。我们日常开发(不打开硬件加速)似乎有没有看到OpenGL es的身影。
其实我们可以做一个大胆的猜测，其实Android的渲染很可能分为2个部分，一个是借助OpenGL es进行渲染，另一个则是通过Skia画笔绘制好像素之后进行渲染。究竟是不是这样呢？不妨留一个悬念，下一篇文章，将会带领大家阅读Android在封装OpenGL es上做了什么努力。
