《Android Framework 之路》BootAnimation（1）

介绍

开机动画，BootAnimation，就是Android手机开机郭晨各种以一个展示给用户的界面，实际是一个多个帧组成的动画，在界面上进行一帧一帧的播放，形成开机动画的效果。
本文针对Android5.1源码分析BootAnimation

源码分析

文件产生

Android平台的开机动画由system/bin下的bootanimation文件完成，而这个文件产生于
frameworks/base/cmds/bootanimation/Android.mk

LOCAL_PATH:= $(call my-dir)
include $(CLEAR_VARS)

LOCAL_SRC_FILES:= \
    bootanimation_main.cpp \
    AudioPlayer.cpp \
    BootAnimation.cpp

LOCAL_CFLAGS += -DGL_GLEXT_PROTOTYPES -DEGL_EGLEXT_PROTOTYPES

LOCAL_C_INCLUDES += external/tinyalsa/include

LOCAL_SHARED_LIBRARIES := \
    libcutils \
    liblog \
    libandroidfw \
    libutils \
    libbinder \
    libui \
    libskia \
    libEGL \
    libGLESv1_CM \
    libgui \
    libtinyalsa

LOCAL_MODULE:= bootanimation

ifdef TARGET_32_BIT_SURFACEFLINGER
LOCAL_32_BIT_ONLY := true
endif
include $(BUILD_EXECUTABLE)

编译结果为bootanimation的bin文件，所以，在有足够权限的前提下，在adb shell下执行bootanimation也是可以看到对应的开机动画效果的。

启动开机动画

开机动画是以bin文件的形式存在于手机系统中，开机过程中通过init.rc定义
system/core/rootdir/init.rc

service bootanim /system/bin/bootanimation
    class core
    user graphics
    group graphics audio
    disabled//定义了disable，在开机过程中不会自动的启动
    oneshot

这里不会启动，那么在哪里启动？由于开机动画对SurfaceFlinger有依赖，所以应该是在SurfaceFlinger启动之后再开始执行，看一下源码。

SurfaceFlinger的启动在init.rc文件中

service surfaceflinger /system/bin/surfaceflinger
    class core
    user system
    group graphics drmrpc
    onrestart restart zygote

与SurfaceFlinger相关的源码存在于
frameworks\native\services\surfaceflinger
入口
frameworks/native/services/surfaceflinger/main_surfaceflinger.cpp

#if defined(HAVE_PTHREADS)
#include <sys/resource.h>
#endif

#include <cutils/sched_policy.h>
#include <binder/IServiceManager.h>
#include <binder/IPCThreadState.h>
#include <binder/ProcessState.h>
#include <binder/IServiceManager.h>
#include "SurfaceFlinger.h"

using namespace android;

int 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 pool
    sp<ProcessState> ps(ProcessState::self());
    ps->startThreadPool();

    // instantiate surfaceflinger
    sp<SurfaceFlinger> flinger = new SurfaceFlinger();

#if defined(HAVE_PTHREADS)
    setpriority(PRIO_PROCESS, 0, PRIORITY_URGENT_DISPLAY);
#endif
    set_sched_policy(0, SP_FOREGROUND);

    // initialize before clients can connect
    flinger->init();//开机动画在这里执行，接着往下看

    // publish surface flinger
    sp<IServiceManager> sm(defaultServiceManager());
    sm->addService(String16(SurfaceFlinger::getServiceName()), flinger, false);

    // run in this thread
    flinger->run();

    return 0;
}

frameworks/native/services/surfaceflinger/SurfaceFlinger.cpp

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

接着执行startBootAnim();

void SurfaceFlinger::startBootAnim() {
    // start boot animation
    property_set("service.bootanim.exit", "0");
    property_set("ctl.start", "bootanim");
}

这里采用的是通过property_set中”ctl.start”的方式执行bootanim,这里是通过设置属性值的方式来启动的，属性值的设置采用的是C/S模式，socket连接，这里不详述，大致说下，这行代码会执行到

system/core/init/property_service.c

void handle_property_set_fd()
{
    ......
    switch(msg.cmd) {
    case PROP_MSG_SETPROP:
        ......
        //这里很关键
        if(memcmp(msg.name,"ctl.",4) == 0) {
            // Keep the old close-socket-early behavior when handling
            // ctl.* properties.
            close(s);
            if (check_control_mac_perms(msg.value, source_ctx)) {
                handle_control_message((char*) msg.name + 4, (char*) msg.value);
            } else {
                ERROR("sys_prop: Unable to %s service ctl [%s] uid:%d gid:%d pid:%d\n",
                        msg.name + 4, msg.value, cr.uid, cr.gid, cr.pid);
            }
         //这里很关键
        } else {
            if (check_perms(msg.name, source_ctx)) {
                property_set((char*) msg.name, (char*) msg.value);
            } else {
                ERROR("sys_prop: permission denied uid:%d  name:%s\n",
                      cr.uid, msg.name);
            }

            // Note: bionic's property client code assumes that the
            // property server will not close the socket until *AFTER*
            // the property is written to memory.
            close(s);
        }
        freecon(source_ctx);
        break;

    default:
        close(s);
        break;
    }
}

接下来执行到
system/core/init/init.c

void handle_control_message(const char *msg, const char *arg)
{
    if (!strcmp(msg,"start")) {
        msg_start(arg);//就是这条路
    } else if (!strcmp(msg,"stop")) {
        msg_stop(arg);
    } else if (!strcmp(msg,"restart")) {
        msg_restart(arg);
    } else {
        ERROR("unknown control msg '%s'\n", msg);
    }
}

接着往下执行

static void msg_start(const char *name)
{
    struct service *svc = NULL;
    char *tmp = NULL;
    char *args = NULL;

    if (!strchr(name, ':'))
        svc = service_find_by_name(name);
    else {
        tmp = strdup(name);
        if (tmp) {
            args = strchr(tmp, ':');
            *args = '\0';
            args++;

            svc = service_find_by_name(tmp);
        }
    }

    if (svc) {
        service_start(svc, args);
    } else {
        ERROR("no such service '%s'\n", name);
    }
    if (tmp)
        free(tmp);
}