安卓高手之路之 GDI图形引擎篇

1.底层C++

SufaceFlinger类图的静态结构

2.上层Java的调用流程。

首先，直接从WindowManagerService入手：

 public int relayoutWindow(Session session, IWindow client, int seq,
            WindowManager.LayoutParams attrs, int requestedWidth,
            int requestedHeight, int viewVisibility, int flags,
            Rect outFrame, Rect outContentInsets, Rect outVisibleInsets,
            Configuration outConfig, Surface outSurface)

这个方法中有一句： Surface surface = win.createSurfaceLocked();
创建Surface，然后继续跟下去，跟到了jni(android_view_Surface.cpp)的如下方法：

static void Surface_init(
        JNIEnv* env, jobject clazz,
        jobject session,
        jint, jstring jname, jint dpy, jint w, jint h, jint format, jint flags)
{
    if (session == NULL) {
        doThrowNPE(env);
        return;
    }

    SurfaceComposerClient* client =
            (SurfaceComposerClient*)env->GetIntField(session, sso.client);

    sp<SurfaceControl> surface;
    if (jname == NULL) {
        surface = client->createSurface(dpy, w, h, format, flags);
    } else {
        const jchar* str = env->GetStringCritical(jname, 0);
        const String8 name(str, env->GetStringLength(jname));
        env->ReleaseStringCritical(jname, str);
        surface = client->createSurface(name, dpy, w, h, format, flags);
    }

    if (surface == 0) {
        jniThrowException(env, OutOfResourcesException, NULL);
        return;
    }
    setSurfaceControl(env, clazz, surface);
}

郁闷的是这个session又是如何初始化的，同样在android_view_Surface.cpp中：

static void SurfaceSession_init(JNIEnv* env, jobject clazz)
{
    sp<SurfaceComposerClient> client = new SurfaceComposerClient;
    client->incStrong(clazz);
    env->SetIntField(clazz, sso.client, (int)client.get());
}

非常好，那么这个client就是和java层SurfaceSession构成了一一对应关系咯？事实的确如此。看java层的 SurfaceSession的定义，里面仅有的成员变量就是这个client：

public class SurfaceSession {
    /** Create a new connection with the surface flinger. */
    public SurfaceSession() {
        init();
    }

    /** Forcibly detach native resources associated with this object.
     *  Unlike destroy(), after this call any surfaces that were created
     *  from the session will no longer work. The session itself is destroyed.
     */
    public native void kill();

    /* no user serviceable parts here ... */
    @Override
    protected void finalize() throws Throwable {
        destroy();
    }
    
    private native void init();
    private native void destroy();
    
    private int mClient;
}

好了，现在回到java层继续看Surface。现在的概念应该很明确了，从本质上来说，Surface是由SurfaceSession创建的。那么SurfaceSession 又是由谁创建的呢？既然SurfaceSession 是Session的成员变量，那么就顺藤摸瓜去看：

  void windowAddedLocked() {
        if (mSurfaceSession == null) {
            if (WindowManagerService.localLOGV) Slog.v(
                WindowManagerService.TAG, "First window added to " + this + ", creating SurfaceSession");
            mSurfaceSession = new SurfaceSession();
            if (WindowManagerService.SHOW_TRANSACTIONS) Slog.i(
                    WindowManagerService.TAG, "  NEW SURFACE SESSION " + mSurfaceSession);
            mService.mSessions.add(this);
        }
        mNumWindow++;
    }

那么windowAddedLocked又是谁调用的呢？在WIndowState.java中：

 void attach() {
        if (WindowManagerService.localLOGV) Slog.v(
            WindowManagerService.TAG, "Attaching " + this + " token=" + mToken
            + ", list=" + mToken.windows);
        mSession.windowAddedLocked();
    }

那么这个attach又是谁调用的呢？WindowManagerService.java的一个方法，如下：

 public int addWindow(Session session, IWindow client, int seq,
            WindowManager.LayoutParams attrs, int viewVisibility,
            Rect outContentInsets, InputChannel outInputChannel)

由于这个方法比较长，就不贴了，只看其中最关键的地方，其中有这么一句话： win.attach(); 经过这么一分析，清楚了，SurfaceSession是WindowManagerService在addWindow的时候创建的。而 Surface是在WIndowManagerService进行relayoutWindow时创建的。

安卓高手之路之 GDI图形引擎篇

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