Android SurfaceFlinger Part 1 - 啟動流程

SurfaceFlinger啟動方法有兩種

• 方法一: 隨著zygote啟動(Default)

       啟動的流程是 main@SystemServer.java ->system_init@com_android_server_SystemServer.cpp

        ->system_init@system_init.cpp

       在system_init的function裡寫著

    property_get("system_init.startsurfaceflinger", propBuf, "1");
        if (strcmp(propBuf, "1") == 0) {
        // Start the SurfaceFlinger
        SurfaceFlinger::instantiate();
    }
     ...
    ProcessState::self()->startThreadPool();
    IPCThreadState::self()->joinThreadPool();

        因此，假設系統中不存在"system_init.startsensorservice"就會執行SurfaceFlinger::instantiate();定義    在BinderService.h 最終執行
 sm->addService(String16(SERVICE::getServiceName()), new SERVICE());
        將surfaceflinger加入系統的service.

• 方法二:直接執行surfaceflinger

       我們可以在例如init.rc裡面直接去啟動surfaceflinger，程式碼位置是main_surfaceflinger.cpp 程式碼的內容是

  int main(int argc, char** argv) {
      SurfaceFlinger::publishAndJoinThreadPool();
      return 0;
  }

     SurfaceFlinger定義在SurfaceFlinger.h，而他是繼承BinderService 定義在BinderService.h 因此，我們可以在  BinderService.h看到 publishAndJoinThreadPool()的實做

    sp proc(ProcessState::self());
    sp sm(defaultServiceManager());
    sm->addService(String16(SERVICE::getServiceName()), new SERVICE());
    ProcessState::self()->startThreadPool();
    IPCThreadState::self()->joinThreadPool();

兩種方法都是利用

 sm->addService(String16(SERVICE::getServiceName()), new SERVICE());   

將surfaceflinger加入service並利用

ProcessState::self()->startThreadPool();
IPCThreadState::self()->joinThreadPool();

進入surfaceflinger裡的

SurfaceFlinger::readyToRun()

定義在Thread::_threadLoop@Threads.cpp

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

readyToRun()會做幾件事:

• 建立GraphicPlane

GraphicPlane& plane(graphicPlane(dpy));
DisplayHardware* const hw = new DisplayHardware(this, dpy);
plane.setDisplayHardware(hw);



在建立DisplayHardware的物件時init()@DisplayHareware，會new 一個FramebufferNativeWindow 的object FramebufferNativeWindow()@FramebufferNativeWindow 然後分別建立fbdev framebuffer_open()@gralloc.h及grdev gralloc_open()@gralloc.h 最後都會透過gralloc_device_open()@gralloc.cpp來建立，

如果是framebuffer的話，會呼叫fb_device_open()@framebuffer.cpp 在裡面要注意的是他透過mapFrameBuffer()->mapFrameBufferLocked()嘗試開啟

char const * const device_template[] = {
    "/dev/graphics/fb%u",
    "/dev/fb%u",
    0 };

與kernel做溝通. 如果是graphic的話就要看平台實做了。


• 初始化EGL
• 取得Display資訊

EGLDisplay display = eglGetDisplay(EGL_DEFAULT_DISPLAY);
eglInitialize(display, NULL, NULL);
eglGetConfigs(display, NULL, 0, &numConfigs);
err = selectConfigForPixelFormat(display, attribs, format, &config);



• 建立main surface by call eglCreateWindowSurface()

surface = eglCreateWindowSurface(display, config, mNativeWindow.get(), NULL);
if (mFlags & PARTIAL_UPDATES) {
    // if we have partial updates, we definitely don't need to
    // preserve the backbuffer, which may be costly.
    eglSurfaceAttrib(display, surface,
                EGL_SWAP_BEHAVIOR, EGL_BUFFER_DESTROYED);
}

• 取得LCD 的density

    if (property_get("qemu.sf.lcd_density", property, NULL) <= 0) {
        if (property_get("ro.sf.lcd_density", property, NULL) <= 0) {
            LOGW("ro.sf.lcd_density not defined, using 160 dpi by default.");
            strcpy(property, "160");
        }
    } else {
        /* for the emulator case, reset the dpi values too */
        mDpiX = mDpiY = atoi(property);
    }
    mDensity = atoi(property) * (1.0f/160.0f);

• 建立的Context

context = eglCreateContext(display, config, NULL, contextAttributes);

context存放著當前的 顏色,texture 等等的資訊
• 暫時 unBind context

eglMakeCurrent(display, EGL_NO_SURFACE, EGL_NO_SURFACE, EGL_NO_CONTEXT);



• 初始化hw composer

mHwc = new HWComposer(mFlinger);
if (mHwc->initCheck() == NO_ERROR) {
    mHwc->setFrameBuffer(mDisplay, mSurface);
}

• Bind context
最後回到readyToRun()透過hw.makeCurrent();來bind context接著就可以開始畫圖了
• 播放動畫

property_set("ctl.start", "bootanim");

在readyToRun()跑完之後，就會進入SurfaceFlinger::threadLoop()在下一篇會討論