SDL.png

项目位置 https://github.com/deepsadness/SDLCmakeDemo

系列内容导读

1. SDL2-移植Android Studio+CMakeList集成
2. Android端FFmpeg +SDL2的简单播放器
3. SDL2 Android端的简要分析(VideoSubSystem)
4. SDL2 Android端的简要分析(AudioSubSystem)

Android 部分源码分析

暂时只包括视频系统的部分。

1. Android上SDLThread启动初始化
2.SDL初始化
SDL_Init(): 初始化SDL。
SDL_CreateWindow(): 创建窗口（Window）。
SDL_CreateRenderer(): 基于窗口创建渲染器（Render）。
SDL_CreateTexture(): 创建纹理（Texture）。
3. SDL循环渲染数据
SDL_UpdateTexture(): 设置纹理的数据。
SDL_RenderCopy(): 纹理复制给渲染器。
SDL_RenderPresent(): 显示。

SDLThread 启动的初始化

根据SDLActivity的初始化流程。来看一下SDL的初始化。

SDLActivity::onCreate方法

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        Log.v(TAG, "Device: " + Build.DEVICE);
        Log.v(TAG, "Model: " + Build.MODEL);
        Log.v(TAG, "onCreate()");
        super.onCreate(savedInstanceState);

        // Load shared libraries
        String errorMsgBrokenLib = "";
        try {
            //加载库
            loadLibraries();
        } catch (UnsatisfiedLinkError e) {
            System.err.println(e.getMessage());
            mBrokenLibraries = true;
            errorMsgBrokenLib = e.getMessage();
        } catch (Exception e) {
            System.err.println(e.getMessage());
            mBrokenLibraries = true;
            errorMsgBrokenLib = e.getMessage();
        }
          
        //没加载成功。就弹出框提示。
        if (mBrokenLibraries) {
            mSingleton = this;
            AlertDialog.Builder dlgAlert = new AlertDialog.Builder(this);
            dlgAlert.setMessage("An error occurred while trying to start the application. Please try again and/or reinstall."
                    + System.getProperty("line.separator")
                    + System.getProperty("line.separator")
                    + "Error: " + errorMsgBrokenLib);
            dlgAlert.setTitle("SDL Error");
            dlgAlert.setPositiveButton("Exit",
                    new DialogInterface.OnClickListener() {
                        @Override
                        public void onClick(DialogInterface dialog, int id) {
                            // if this button is clicked, close current activity
                            SDLActivity.mSingleton.finish();
                        }
                    });
            dlgAlert.setCancelable(false);
            dlgAlert.create().show();

            return;
        }

        // Set up JNI
        SDL.setupJNI();

        // Initialize state
        SDL.initialize();

        // So we can call stuff from static callbacks
        mSingleton = this;
        SDL.setContext(this);

      // 剪贴板
        if (Build.VERSION.SDK_INT >= 11) {
            mClipboardHandler = new SDLClipboardHandler_API11();
        } else {
            /* Before API 11, no clipboard notification (eg no SDL_CLIPBOARDUPDATE) */
            mClipboardHandler = new SDLClipboardHandler_Old();
        }
      
        //HID device
        mHIDDeviceManager = HIDDeviceManager.acquire(this);

        //创建Surface 
        mSurface = new SDLSurface(getApplication());

        mLayout = new RelativeLayout(this);
        mLayout.addView(mSurface);

        // Get our current screen orientation and pass it down.
        mCurrentOrientation = SDLActivity.getCurrentOrientation();
        SDLActivity.onNativeOrientationChanged(mCurrentOrientation);

        setContentView(mLayout);

        setWindowStyle(false);

        getWindow().getDecorView().setOnSystemUiVisibilityChangeListener(this);

        // Get filename from "Open with" of another application
        Intent intent = getIntent();
        if (intent != null && intent.getData() != null) {
            String filename = intent.getData().getPath();
            if (filename != null) {
                Log.v(TAG, "Got filename: " + filename);
                SDLActivity.onNativeDropFile(filename);
            }
        }
    }

• loadLibraries

//这个方法，可以看到就是我们之前的定义的库的名称。如果我们在CMakeList.txt中修改了自己编译的库的名称。那这里也要记得修改。
 protected String[] getLibraries() {
        return new String[]{
                "SDL2",
                // "SDL2_image",
                // "SDL2_mixer",
                // "SDL2_net",
                // "SDL2_ttf",
                "main"
        };
    }
 // Load the .so
    public void loadLibraries() {
        for (String lib : getLibraries()) {
            SDL.loadLibrary(lib);
        }
    }

  //如果添加了com.getkeepsafe.relinker.ReLinker这个库，就会用它就加载。没有的话，就系统默认的方法。
  public static void loadLibrary(String libraryName) throws UnsatisfiedLinkError, SecurityException, NullPointerException {

        if (libraryName == null) {
            throw new NullPointerException("No library name provided.");
        }

        try {
            Class relinkClass = mContext.getClassLoader().loadClass("com.getkeepsafe.relinker.ReLinker");
            Class relinkListenerClass = mContext.getClassLoader().loadClass("com.getkeepsafe.relinker.ReLinker$LoadListener");
            Class contextClass = mContext.getClassLoader().loadClass("android.content.Context");
            Class stringClass = mContext.getClassLoader().loadClass("java.lang.String");

            // Get a 'force' instance of the ReLinker, so we can ensure libraries are reinstalled if 
            // they've changed during updates.
            Method forceMethod = relinkClass.getDeclaredMethod("force");
            Object relinkInstance = forceMethod.invoke(null);
            Class relinkInstanceClass = relinkInstance.getClass();

            // Actually load the library!
            Method loadMethod = relinkInstanceClass.getDeclaredMethod("loadLibrary", contextClass, stringClass, stringClass, relinkListenerClass);
            loadMethod.invoke(relinkInstance, mContext, libraryName, null, null);
        }
        catch (final Throwable e) {
            // Fall back
            try {
                System.loadLibrary(libraryName);
            }
            catch (final UnsatisfiedLinkError ule) {
                throw ule;
            }
            catch (final SecurityException se) {
                throw se;
            }
        }        
    }

SDL.setupJNI()

这个方法会对SDL中的模块进行初始化。

   public static void setupJNI() {
        //SDLActivity中的JNI方法进行初始化。可以一定程度的认为是音频系统的初始化
        SDLActivity.nativeSetupJNI();
        //音频系统的初始化
        SDLAudioManager.nativeSetupJNI();
        // 控制系统的初始化
        SDLControllerManager.nativeSetupJNI();
    }

SDLActivity::nativeSetUpJNI

进入到SDL_android.c文件中。
我们首先来看一下方法签名的定义方式。这里和通常直接写方法签名的方式不同。
SDL使用拼接的方式，来完成我们的JNI方法的定义的。

#define SDL_JAVA_PREFIX                                 org_libsdl_app
#define CONCAT1(prefix, class, function)                CONCAT2(prefix, class, function)
#define CONCAT2(prefix, class, function)                Java_ ## prefix ## _ ## class ## _ ## function
#define SDL_JAVA_INTERFACE(function)                    CONCAT1(SDL_JAVA_PREFIX, SDLActivity, function)

这样的好处，是我们可以方便的修改JNI方法的类。

目前的包名和类名.png

如果我们修改了包名和类名。只要过来修改这两个宏的值就可以了。
是不是超级方便~
其实如果熟悉JNI的话，也会很清楚JNI方法名定义的套路的。就和这里的CONCAT2宏定义的一样。这儿就不细说了。
定义的话，就接着自己补齐JNIEXPORT 和返回的变量 和变量名称和参数签名就可以了。

• nativeSetupJNI的完整方法签名

/* Java class SDLActivity */
JNIEXPORT void JNICALL SDL_JAVA_INTERFACE(nativeSetupJNI)(
        JNIEnv* mEnv, jclass cls);

因为这些都和包名和类没有关系，所以通过这样的宏，就可以把两者解耦，达到随意改类名和包名了。

• nativeSetupJNI的方法实现

1. 将当前的线程attached到当前APP的JVM线程当中

JNIEnv* Android_JNI_GetEnv(void)
{
    /*根据JNI的调试，所有的线程都是Linux线程，在c中创建了线程，并且attached 到    
     JavaVM上。
     在该线程上就可以有了JVM环境，可以调用JNI的方法。
     如果attached 一个原生创建的线程会直接在main 线程组创建一个线程对象。
     AttachCurrentThread可以随意调用。不管是否已经attached过。
    */
    JNIEnv *env;
    int status = (*mJavaVM)->AttachCurrentThread(mJavaVM, &env, NULL);
    if(status < 0) {
        LOGE("failed to attach current thread");
        return 0;
    }

    /* 调用了这个方法，就是在thread_local中把JNIEnv保存起来。
      这样的话，会自动创建一个解构方法，在线程终止时。该解构方法，会自动调用DetachCurrentThread 。
      因为AttachCurrentThread 和DetachCurrentThread  方法是期待成对出现的。我们用了下面方法，就可以不自己写DetachCurrentThread  了。
    */
    pthread_setspecific(mThreadKey, (void*) env);

    return env;
}

//上面的mThreadKey，是在加载库初始化的是，创建的如下。对应的解构函数也是自己传入的。
JNIEXPORT jint JNICALL JNI_OnLoad(JavaVM* vm, void* reserved)
{
    JNIEnv *env;
    mJavaVM = vm;
    LOGI("JNI_OnLoad called");
    if ((*mJavaVM)->GetEnv(mJavaVM, (void**) &env, JNI_VERSION_1_4) != JNI_OK) {
        LOGE("Failed to get the environment using GetEnv()");
        return -1;
    }
    if (pthread_key_create(&mThreadKey, Android_JNI_ThreadDestroyed) != 0) {
        __android_log_print(ANDROID_LOG_ERROR, "SDL", "Error initializing pthread key");
    }
    Android_JNI_SetupThread();

    return JNI_VERSION_1_4;
}

static void Android_JNI_ThreadDestroyed(void* value)
{
    /* The thread is being destroyed, detach it from the Java VM and set the mThreadKey value to NULL as required */
    JNIEnv *env = (JNIEnv*) value;
    if (env != NULL) {
        (*mJavaVM)->DetachCurrentThread(mJavaVM);
        pthread_setspecific(mThreadKey, NULL);
    }
}

总结下来，创建mThreadKey有两个好处。

1. 可以在JVM调试的时候，对给线程进行调试
2. 可以传入解构函数

2. 就是讲需要通过JNI调用的Native方法的函数都缓存起来。

    mActivityClass = (jclass)((*mEnv)->NewGlobalRef(mEnv, cls));

    midGetNativeSurface = (*mEnv)->GetStaticMethodID(mEnv, mActivityClass,
                                "getNativeSurface","()Landroid/view/Surface;");
    midSetActivityTitle = (*mEnv)->GetStaticMethodID(mEnv, mActivityClass,
                                "setActivityTitle","(Ljava/lang/String;)Z");
    midSetWindowStyle = (*mEnv)->GetStaticMethodID(mEnv, mActivityClass,
                                "setWindowStyle","(Z)V");
    midSetOrientation = (*mEnv)->GetStaticMethodID(mEnv, mActivityClass,
                                "setOrientation","(IIZLjava/lang/String;)V");
    midGetContext = (*mEnv)->GetStaticMethodID(mEnv, mActivityClass,
                                "getContext","()Landroid/content/Context;");
    midIsTablet = (*mEnv)->GetStaticMethodID(mEnv, mActivityClass,
                                "isTablet", "()Z");
    midIsAndroidTV = (*mEnv)->GetStaticMethodID(mEnv, mActivityClass,
                                "isAndroidTV","()Z");
    midIsChromebook = (*mEnv)->GetStaticMethodID(mEnv, mActivityClass,
                                "isChromebook", "()Z");
    midIsDeXMode = (*mEnv)->GetStaticMethodID(mEnv, mActivityClass,
                                "isDeXMode", "()Z");
    midManualBackButton = (*mEnv)->GetStaticMethodID(mEnv, mActivityClass,
                                "manualBackButton", "()V");
    midInputGetInputDeviceIds = (*mEnv)->GetStaticMethodID(mEnv, mActivityClass,
                                "inputGetInputDeviceIds", "(I)[I");
    midSendMessage = (*mEnv)->GetStaticMethodID(mEnv, mActivityClass,
                                "sendMessage", "(II)Z");
    midShowTextInput =  (*mEnv)->GetStaticMethodID(mEnv, mActivityClass,
                                "showTextInput", "(IIII)Z");
    midIsScreenKeyboardShown = (*mEnv)->GetStaticMethodID(mEnv, mActivityClass,
                                "isScreenKeyboardShown","()Z");
    midClipboardSetText = (*mEnv)->GetStaticMethodID(mEnv, mActivityClass,
                                "clipboardSetText", "(Ljava/lang/String;)V");
    midClipboardGetText = (*mEnv)->GetStaticMethodID(mEnv, mActivityClass,
                                "clipboardGetText", "()Ljava/lang/String;");
    midClipboardHasText = (*mEnv)->GetStaticMethodID(mEnv, mActivityClass,
                                "clipboardHasText", "()Z");
    midOpenAPKExpansionInputStream = (*mEnv)->GetStaticMethodID(mEnv, mActivityClass,
                                "openAPKExpansionInputStream", "(Ljava/lang/String;)Ljava/io/InputStream;");

    midGetManifestEnvironmentVariables = (*mEnv)->GetStaticMethodID(mEnv, mActivityClass,
                                "getManifestEnvironmentVariables", "()Z");

    midGetDisplayDPI = (*mEnv)->GetStaticMethodID(mEnv, mActivityClass, "getDisplayDPI", "()Landroid/util/DisplayMetrics;");
    midCreateCustomCursor = (*mEnv)->GetStaticMethodID(mEnv, mActivityClass, "createCustomCursor", "([IIIII)I");
    midSetCustomCursor = (*mEnv)->GetStaticMethodID(mEnv, mActivityClass, "setCustomCursor", "(I)Z");
    midSetSystemCursor = (*mEnv)->GetStaticMethodID(mEnv, mActivityClass, "setSystemCursor", "(I)Z");

    midSupportsRelativeMouse = (*mEnv)->GetStaticMethodID(mEnv, mActivityClass, "supportsRelativeMouse", "()Z");
    midSetRelativeMouseEnabled = (*mEnv)->GetStaticMethodID(mEnv, mActivityClass, "setRelativeMouseEnabled", "(Z)Z");


    if (!midGetNativeSurface ||
       !midSetActivityTitle || !midSetWindowStyle || !midSetOrientation || !midGetContext || !midIsTablet || !midIsAndroidTV || !midInputGetInputDeviceIds ||
       !midSendMessage || !midShowTextInput || !midIsScreenKeyboardShown ||
       !midClipboardSetText || !midClipboardGetText || !midClipboardHasText ||
       !midOpenAPKExpansionInputStream || !midGetManifestEnvironmentVariables || !midGetDisplayDPI ||
       !midCreateCustomCursor || !midSetCustomCursor || !midSetSystemCursor || !midSupportsRelativeMouse || !midSetRelativeMouseEnabled ||
       !midIsChromebook || !midIsDeXMode || !midManualBackButton) {
        __android_log_print(ANDROID_LOG_WARN, "SDL", "Missing some Java callbacks, do you have the latest version of SDLActivity.java?");
    }

    fidSeparateMouseAndTouch = (*mEnv)->GetStaticFieldID(mEnv, mActivityClass, "mSeparateMouseAndTouch", "Z");

    if (!fidSeparateMouseAndTouch) {
        __android_log_print(ANDROID_LOG_WARN, "SDL", "Missing some Java static fields, do you have the latest version of SDLActivity.java?");
    }

3. 检查是否初始化完成。
   这里要上面三个模块，全部初始化完整之后，就会将进入SDL_SetMainReady状态

void checkJNIReady()
{
    if (!mActivityClass || !mAudioManagerClass || !mControllerManagerClass) {
        // We aren't fully initialized, let's just return.
        return;
    }

    SDL_SetMainReady();    
}

剩下的SDLAudioManager.nativeSetupJNI()和SDLControllerManager.nativeSetupJNI()也基本上一样。就不看了。

SDL.initialize()
初始化上面三个的java对象

创建SDLSurface，并添加到跟布局中。
后面还有一些参数设置。

下面就进入SDLSurface的生命周期当中。

在SDLSurface的对应的生命周期中，会调用handleNativeState对Native的State进行修改。

  /* Transition to next state */
    public static void handleNativeState() {

        if (mNextNativeState == mCurrentNativeState) {
            // Already in same state, discard.
            return;
        }

        // Try a transition to init state
        if (mNextNativeState == NativeState.INIT) {

            mCurrentNativeState = mNextNativeState;
            return;
        }

        // Try a transition to paused state
        if (mNextNativeState == NativeState.PAUSED) {
            nativePause();
            if (mSurface != null)
                mSurface.handlePause();
            mCurrentNativeState = mNextNativeState;
            return;
        }

        // Try a transition to resumed state
        if (mNextNativeState == NativeState.RESUMED) {
            if (mIsSurfaceReady && mHasFocus && mIsResumedCalled) {
                if (mSDLThread == null) {
                    // This is the entry point to the C app.
                    // Start up the C app thread and enable sensor input for the first time
                    // FIXME: Why aren't we enabling sensor input at start?

                    mSDLThread = new Thread(new SDLMain(), "SDLThread");
                    mSurface.enableSensor(Sensor.TYPE_ACCELEROMETER, true);
                    mSDLThread.start();
                }

                nativeResume();
                mSurface.handleResume();
                mCurrentNativeState = mNextNativeState;
            }
        }
    }

在Resume的状态中，会启动一个SDLThread线程。
线程运行下面这个Runnable .

class SDLMain implements Runnable {
    @Override
    public void run() {
        //得到我们在Activity中定义的参数。
        String library = SDLActivity.mSingleton.getMainSharedObject();
        //确定运行的朱主函数名称。这里是SDL_main
        String function = SDLActivity.mSingleton.getMainFunction();
       //我们定义的getArguments 这个在上一遍文章，我们就见过了。并且我们传递了自己的视频路径
        String[] arguments = SDLActivity.mSingleton.getArguments();
        
        // 运行nativeRunMain JNI方法
        Log.v("SDL", "Running main function " + function + " from library " + library);
        SDLActivity.nativeRunMain(library, function, arguments);

        Log.v("SDL", "Finished main function");

        // Native thread has finished, let's finish the Activity
        if (!SDLActivity.mExitCalledFromJava) {
            SDLActivity.handleNativeExit();
        }
    }
}

SDLActivity.java::getMainSharedObject()
这个方法会把我们原来写的 main拼接成正确的名字 libmain.so
注意这个函数，是去取数组的最后一个库，作为主函数坐在的库的。所以如果修改传递的时候，一定要小心。我们现在的主函数库就是libmain

    protected String getMainSharedObject() {
        String library;
        String[] libraries = SDLActivity.mSingleton.getLibraries();
        if (libraries.length > 0) {
            library = "lib" + libraries[libraries.length - 1] + ".so";
        } else {
            library = "libmain.so";
        }
        return getContext().getApplicationInfo().nativeLibraryDir + "/" + library;
    }

这里对应的定义了主函数的library和主函数的名称。就是对应了当前项目下的
这个库的名字是我们在CMakeList当中配置的。

CMakeList中的配置

我们这里传入的主函数名称是SDL_Main,在SDL_main.h中，由宏定义的。其实对应的是main方法

SDL_main中的宏 SDL_main指向main.png

.png

进入到nativeRunMain 这个主函数中取看看

/* 开启整个 SDL app的方法，运行在SDLThread当中 */
JNIEXPORT int JNICALL SDL_JAVA_INTERFACE(nativeRunMain)(JNIEnv* env, jclass cls, jstring library, jstring function, jobject array)
{
    int status = -1;
    const char *library_file;
    void *library_handle;

    __android_log_print(ANDROID_LOG_VERBOSE, "SDL", "nativeRunMain()");
    
    // 会使用dlopen打开我们传入的library
    library_file = (*env)->GetStringUTFChars(env, library, NULL);
    library_handle = dlopen(library_file, RTLD_GLOBAL);
    if (library_handle) {
        const char *function_name;
        SDL_main_func SDL_main;

        function_name = (*env)->GetStringUTFChars(env, function, NULL);
        //并且用dlsym 根据我们的函数库和函数名，打开我们定义的主方法。
        SDL_main = (SDL_main_func)dlsym(library_handle, function_name);
        if (SDL_main) {
            int i;
            int argc;
            int len;
            char **argv;
          
            //传入参数
            /* Prepare the arguments. */
            len = (*env)->GetArrayLength(env, array);
            argv = SDL_stack_alloc(char*, 1 + len + 1);
            argc = 0;
            //这里上一遍文章说过，第一个参数是app_process
            /* Use the name "app_process" so PHYSFS_platformCalcBaseDir() works.
               https://bitbucket.org/MartinFelis/love-android-sdl2/issue/23/release-build-crash-on-start
             */
            argv[argc++] = SDL_strdup("app_process");
            for (i = 0; i < len; ++i) {
                const char* utf;
                char* arg = NULL;
                jstring string = (*env)->GetObjectArrayElement(env, array, i);
                if (string) {
                    utf = (*env)->GetStringUTFChars(env, string, 0);
                    if (utf) {
                        arg = SDL_strdup(utf);
                        (*env)->ReleaseStringUTFChars(env, string, utf);
                    }
                    (*env)->DeleteLocalRef(env, string);
                }
                if (!arg) {
                    arg = SDL_strdup("");
                }
                argv[argc++] = arg;
            }
            argv[argc] = NULL;

            
            /*最后开始运行 */
            status = SDL_main(argc, argv);

            /* Release the arguments. */
            for (i = 0; i < argc; ++i) {
                SDL_free(argv[i]);
            }
            SDL_stack_free(argv);

        } else {
            __android_log_print(ANDROID_LOG_ERROR, "SDL", "nativeRunMain(): Couldn't find function %s in library %s", function_name, library_file);
        }
        (*env)->ReleaseStringUTFChars(env, function, function_name);

        //循环退出之后。dlclose这个库
        dlclose(library_handle);

    } else {
        __android_log_print(ANDROID_LOG_ERROR, "SDL", "nativeRunMain(): Couldn't load library %s", library_file);
    }
    (*env)->ReleaseStringUTFChars(env, library, library_file);
    
    //这一这里，只是终止的是我们的SDLThread而已。
    /* Do not issue an exit or the whole application will terminate instead of just the SDL thread */
    /* exit(status); */

    return status;
}

这样就开始进入到我们自己的
native-lib-su.cpp中的main方法了。

SDL流程

SDL_Init 方法

参考雷博士的图，只保留了视频和Android的部分.png

从SDL_InitSubSystem(SDL.c)开始初始化。

• SDL_TicksInit()
  进入到unix/SDL_systimer.c
  方法只是记录了开始的时间。
  在这个文件中，我们可以看到经常用的SDL_Delay 就在这里。
• SDL_Delay

void
SDL_Delay(Uint32 ms)
{
    int was_error;

#if HAVE_NANOSLEEP
    struct timespec elapsed, tv;
#else
    struct timeval tv;
    Uint32 then, now, elapsed;
#endif

    /* Set the timeout interval */
#if HAVE_NANOSLEEP
    elapsed.tv_sec = ms / 1000;
    elapsed.tv_nsec = (ms % 1000) * 1000000;
#else
    then = SDL_GetTicks();
#endif
    do {
        errno = 0;

#if HAVE_NANOSLEEP
        tv.tv_sec = elapsed.tv_sec;
        tv.tv_nsec = elapsed.tv_nsec;
        was_error = nanosleep(&tv, &elapsed);
#else
        /* Calculate the time interval left (in case of interrupt) */
        now = SDL_GetTicks();
        elapsed = (now - then);
        then = now;
        if (elapsed >= ms) {
            break;
        }
        ms -= elapsed;
        tv.tv_sec = ms / 1000;
        tv.tv_usec = (ms % 1000) * 1000;

        was_error = select(0, NULL, NULL, NULL, &tv);
#endif /* HAVE_NANOSLEEP */
    } while (was_error && (errno == EINTR));
}

#endif /* SDL_TIMER_UNIX */

/* vi: set ts=4 sw=4 expandtab: */

• SDL_StartEventLoop
  这个方法中，如果是多线程的话，就会创建互斥锁。
  然后通常的配置是禁用掉。
  下面三种事件

    SDL_EventState(SDL_TEXTINPUT, SDL_DISABLE);
    SDL_EventState(SDL_TEXTEDITING, SDL_DISABLE);
    SDL_EventState(SDL_SYSWMEVENT, SDL_DISABLE);

• SDL_TimerInit
  简单的理解就是通过SDL_CreateThreadInternal 创建了一个Timer线程。

下面就进入视频系统的初始化

• SDL_VideoInit(SDL_video.c)
• Android_InitKeyboard 、Android_InitTouch 、Android_InitMouse
  都是通过JNI方法，分别初始化键盘的数组和touch device Id 和Cursor.(setCustomCursor 对应的是android.view.PointerIcon？)

• VideoBootStrap->available()和VideoBootStrap->create()
VideoBootStrap,因为在Android平台下，所以对应的是Android_bootstrap分别调用
  在SDL_androidvideo.c中Android_Available方法和Android_CreateDevice方法。
• Android_Available
  Android_Available方法总是返回1，表示可用。因为只有编译在Android平台时，才会去初始化这个Android_bootstrap。
• Android_CreateDevice

static SDL_VideoDevice *
Android_CreateDevice(int devindex)
{
    SDL_VideoDevice *device;
    SDL_VideoData *data;

    /* Initialize all variables that we clean on shutdown */
    device = (SDL_VideoDevice *) SDL_calloc(1, sizeof(SDL_VideoDevice));
    if (!device) {
        SDL_OutOfMemory();
        return NULL;
    }

    data = (SDL_VideoData*) SDL_calloc(1, sizeof(SDL_VideoData));
    if (!data) {
        SDL_OutOfMemory();
        SDL_free(device);
        return NULL;
    }

    device->driverdata = data;

    /* Set the function pointers */
    device->VideoInit = Android_VideoInit;
    device->VideoQuit = Android_VideoQuit;
    device->PumpEvents = Android_PumpEvents;

    device->GetDisplayDPI = Android_GetDisplayDPI;

    device->CreateSDLWindow = Android_CreateWindow;
    device->SetWindowTitle = Android_SetWindowTitle;
    device->SetWindowFullscreen = Android_SetWindowFullscreen;
    device->DestroyWindow = Android_DestroyWindow;
    device->GetWindowWMInfo = Android_GetWindowWMInfo;

    device->free = Android_DeleteDevice;

    /* GL pointers */
    device->GL_LoadLibrary = Android_GLES_LoadLibrary;
    device->GL_GetProcAddress = Android_GLES_GetProcAddress;
    device->GL_UnloadLibrary = Android_GLES_UnloadLibrary;
    device->GL_CreateContext = Android_GLES_CreateContext;
    device->GL_MakeCurrent = Android_GLES_MakeCurrent;
    device->GL_SetSwapInterval = Android_GLES_SetSwapInterval;
    device->GL_GetSwapInterval = Android_GLES_GetSwapInterval;
    device->GL_SwapWindow = Android_GLES_SwapWindow;
    device->GL_DeleteContext = Android_GLES_DeleteContext;

#if SDL_VIDEO_VULKAN
    device->Vulkan_LoadLibrary = Android_Vulkan_LoadLibrary;
    device->Vulkan_UnloadLibrary = Android_Vulkan_UnloadLibrary;
    device->Vulkan_GetInstanceExtensions = Android_Vulkan_GetInstanceExtensions;
    device->Vulkan_CreateSurface = Android_Vulkan_CreateSurface;
#endif

    /* Screensaver */
    device->SuspendScreenSaver = Android_SuspendScreenSaver;

    /* Text input */
    device->StartTextInput = Android_StartTextInput;
    device->StopTextInput = Android_StopTextInput;
    device->SetTextInputRect = Android_SetTextInputRect;

    /* Screen keyboard */
    device->HasScreenKeyboardSupport = Android_HasScreenKeyboardSupport;
    device->IsScreenKeyboardShown = Android_IsScreenKeyboardShown;

    /* Clipboard */
    device->SetClipboardText = Android_SetClipboardText;
    device->GetClipboardText = Android_GetClipboardText;
    device->HasClipboardText = Android_HasClipboardText;

    return device;
}

其实可以看到这里如果不是使用Vulcan的话，就使用的是OpenGLes

这些个方法指针，其实提前都被定义好了。
基本上都是GL的方法，其他的都在对应的java类中。最开始初始化的时候，能够看到。

• SDL_AudioInit
  同样进入SDL_androidaudio.c中。
  ANDROIDAUDIO_Init相关的方法，都在AudioManager当中。暂时省略不提。

其他的暂时不看了。

SDL_Window 初始化

简化只显示Android部分.png

SDL_init之后，我们就创建了SDL_window

在SDL_Init之后，就进入了SDL_CreateWindow .png

• SDL_CreateWindow 方法

参数含义如下。
title ：窗口标题
x ：窗口位置x坐标。也可以设置为SDL_WINDOWPOS_CENTERED或SDL_WINDOWPOS_UNDEFINED。
y ：窗口位置y坐标。同上。
w ：窗口的宽
h ：窗口的高
flags ：支持下列标识。包括了窗口的是否最大化、最小化，能否调整边界等等属性。
::SDL_WINDOW_FULLSCREEN, ::SDL_WINDOW_OPENGL,
::SDL_WINDOW_HIDDEN, ::SDL_WINDOW_BORDERLESS,
::SDL_WINDOW_RESIZABLE, ::SDL_WINDOW_MAXIMIZED,
::SDL_WINDOW_MINIMIZED, ::SDL_WINDOW_INPUT_GRABBED,
::SDL_WINDOW_ALLOW_HIGHDPI.
返回创建完成的窗口的ID。如果创建失败则返回0。

会进入SDL_androidwindow.c中去创建Window
给window 设置上各种Flag
会通过SDLSurface中的getNativeSurface，然后通过ANativeWindow_fromSurface来获取一个NativeWindow。

SDL_EGL_CreateSurface 然后创建传递给OpenGL 作为Surface
在SDL_egl.c中

EGLSurface *
SDL_EGL_CreateSurface(_THIS, NativeWindowType nw) 
{
    /* max 2 values plus terminator. */
    EGLint attribs[3];
    int attr = 0;

    EGLSurface * surface;

    if (SDL_EGL_ChooseConfig(_this) != 0) {
        return EGL_NO_SURFACE;
    }
    
#if SDL_VIDEO_DRIVER_ANDROID
    {
        /* Android docs recommend doing this!
         * Ref: http://developer.android.com/reference/android/app/NativeActivity.html 
         */
        EGLint format;
        _this->egl_data->eglGetConfigAttrib(_this->egl_data->egl_display,
                                            _this->egl_data->egl_config, 
                                            EGL_NATIVE_VISUAL_ID, &format);

        ANativeWindow_setBuffersGeometry(nw, 0, 0, format);
    }
#endif    
    if (_this->gl_config.framebuffer_srgb_capable) {
#ifdef EGL_KHR_gl_colorspace
        if (SDL_EGL_HasExtension(_this, SDL_EGL_DISPLAY_EXTENSION, "EGL_KHR_gl_colorspace")) {
            attribs[attr++] = EGL_GL_COLORSPACE_KHR;
            attribs[attr++] = EGL_GL_COLORSPACE_SRGB_KHR;
        } else
#endif
        {
            SDL_SetError("EGL implementation does not support sRGB system framebuffers");
            return EGL_NO_SURFACE;
        }
    }

    attribs[attr++] = EGL_NONE;
    
    surface = _this->egl_data->eglCreateWindowSurface(
            _this->egl_data->egl_display,
            _this->egl_data->egl_config,
            nw, &attribs[0]);
    if (surface == EGL_NO_SURFACE) {
        SDL_EGL_SetError("unable to create an EGL window surface", "eglCreateWindowSurface");
    }
    return surface;
}

可以看到这个过程中，创建OpenGL的步骤其实和java中创建基本上一样的。
额外需要做的是，NativeWindow需要ANativeWindow_setBuffersGeometry 方法，先设置一次Buffer的大小。

接下来是
SDL_SetWindowTitle
也是调用SDLActivity中的方法

接下来是SDL _FinishWindowCreation

static void
SDL_FinishWindowCreation(SDL_Window *window, Uint32 flags)
{
    PrepareDragAndDropSupport(window);

    if (flags & SDL_WINDOW_MAXIMIZED) {
        SDL_MaximizeWindow(window);
    }
    if (flags & SDL_WINDOW_MINIMIZED) {
        SDL_MinimizeWindow(window);
    }
    if (flags & SDL_WINDOW_FULLSCREEN) {
        SDL_SetWindowFullscreen(window, flags);
    }
    if (flags & SDL_WINDOW_INPUT_GRABBED) {
        SDL_SetWindowGrab(window, SDL_TRUE);
    }
    if (!(flags & SDL_WINDOW_HIDDEN)) {
        SDL_ShowWindow(window);
    }
}

其实就是设置window的各种状态
这几个方法，android中基本上都没有。只有设置SetWindowFullscreen 有对应的方法
先会去调用setWindowStyle方法，然后修改nativeWindow 的大小。

SDL_androidwindow.c

void
Android_SetWindowFullscreen(_THIS, SDL_Window * window, SDL_VideoDisplay * display, SDL_bool fullscreen)
{
    /* If the window is being destroyed don't change visible state */
    if (!window->is_destroying) {
        Android_JNI_SetWindowStyle(fullscreen);
    }

    /* Ensure our size matches reality after we've executed the window style change.
     *
     * It is possible that we've set width and height to the full-size display, but on
     * Samsung DeX or Chromebooks or other windowed Android environemtns, our window may 
     * still not be the full display size.
     */
    if (!SDL_IsDeXMode() && !SDL_IsChromebook()) {
        return;
    }

    SDL_WindowData * data = (SDL_WindowData *)window->driverdata;

    if (!data || !data->native_window) {
        return;
    }

    int old_w = window->w;
    int old_h = window->h;

    int new_w = ANativeWindow_getWidth(data->native_window);
    int new_h = ANativeWindow_getHeight(data->native_window);

    if (old_w != new_w || old_h != new_h) {
        SDL_SendWindowEvent(window, SDL_WINDOWEVENT_RESIZED, new_w, new_h);
    }
}

SDL_window 结构

/**
 *  \brief The type used to identify a window
 *
 *  \sa SDL_CreateWindow()
 *  \sa SDL_CreateWindowFrom()
 *  \sa SDL_DestroyWindow()
 *  \sa SDL_GetWindowData()
 *  \sa SDL_GetWindowFlags()
 *  \sa SDL_GetWindowGrab()
 *  \sa SDL_GetWindowPosition()
 *  \sa SDL_GetWindowSize()
 *  \sa SDL_GetWindowTitle()
 *  \sa SDL_HideWindow()
 *  \sa SDL_MaximizeWindow()
 *  \sa SDL_MinimizeWindow()
 *  \sa SDL_RaiseWindow()
 *  \sa SDL_RestoreWindow()
 *  \sa SDL_SetWindowData()
 *  \sa SDL_SetWindowFullscreen()
 *  \sa SDL_SetWindowGrab()
 *  \sa SDL_SetWindowIcon()
 *  \sa SDL_SetWindowPosition()
 *  \sa SDL_SetWindowSize()
 *  \sa SDL_SetWindowBordered()
 *  \sa SDL_SetWindowResizable()
 *  \sa SDL_SetWindowTitle()
 *  \sa SDL_ShowWindow()
 */
typedef struct SDL_Window SDL_Window;

typedef struct
{
    EGLSurface egl_surface;
    EGLContext egl_context; /* We use this to preserve the context when losing focus */
    ANativeWindow* native_window;
    
} SDL_WindowData;

3. 渲染器的初始化

   
   
   SDL_CreateRenderer.png

SDL_CreateRenderer

/**
 *  \brief Create a 2D rendering context for a window.
 *
 *  \param window The window where rendering is displayed.
 *  \param index    The index of the rendering driver to initialize, or -1 to
 *                  initialize the first one supporting the requested flags.
 *  \param flags    ::SDL_RendererFlags.
 *
 *  \return A valid rendering context or NULL if there was an error.
 *
 *  \sa SDL_CreateSoftwareRenderer()
 *  \sa SDL_GetRendererInfo()
 *  \sa SDL_DestroyRenderer()
 */

1. 判断是否已经被连接了window 了
2. 同样去driver中，去得到争取的Renderer
   可以看到Android中，用的是GLRenderer

#if SDL_VIDEO_RENDER_OGL_ES2
    &GLES2_RenderDriver,
#endif
#if SDL_VIDEO_RENDER_OGL_ES
    &GLES_RenderDriver,
#endif

GLES2_RenderDriver

SDL_RenderDriver GLES2_RenderDriver = {
    GLES2_CreateRenderer,
    {
        "opengles2",
        (SDL_RENDERER_ACCELERATED | SDL_RENDERER_PRESENTVSYNC | SDL_RENDERER_TARGETTEXTURE),
        4,
        {
        SDL_PIXELFORMAT_ARGB8888,
        SDL_PIXELFORMAT_ABGR8888,
        SDL_PIXELFORMAT_RGB888,
        SDL_PIXELFORMAT_BGR888
        },
        0,
        0
    }
};

SDL_render_gles2 中
GLES2_CreateRenderer 方法

static SDL_Renderer *
GLES2_CreateRenderer(SDL_Window *window, Uint32 flags)
{
    SDL_Renderer *renderer;
    GLES2_DriverContext *data;
    GLint nFormats;
#ifndef ZUNE_HD
    GLboolean hasCompiler;
#endif
    Uint32 window_flags = 0; /* -Wconditional-uninitialized */
    GLint window_framebuffer;
    GLint value;
    int profile_mask = 0, major = 0, minor = 0;
    SDL_bool changed_window = SDL_FALSE;

    if (SDL_GL_GetAttribute(SDL_GL_CONTEXT_PROFILE_MASK, &profile_mask) < 0) {
        goto error;
    }
    if (SDL_GL_GetAttribute(SDL_GL_CONTEXT_MAJOR_VERSION, &major) < 0) {
        goto error;
    }
    if (SDL_GL_GetAttribute(SDL_GL_CONTEXT_MINOR_VERSION, &minor) < 0) {
        goto error;
    }

    window_flags = SDL_GetWindowFlags(window);
    /* OpenGL ES 3.0 is a superset of OpenGL ES 2.0 */
    if (!(window_flags & SDL_WINDOW_OPENGL) ||
        profile_mask != SDL_GL_CONTEXT_PROFILE_ES || major < RENDERER_CONTEXT_MAJOR) {

        changed_window = SDL_TRUE;
        SDL_GL_SetAttribute(SDL_GL_CONTEXT_PROFILE_MASK, SDL_GL_CONTEXT_PROFILE_ES);
        SDL_GL_SetAttribute(SDL_GL_CONTEXT_MAJOR_VERSION, RENDERER_CONTEXT_MAJOR);
        SDL_GL_SetAttribute(SDL_GL_CONTEXT_MINOR_VERSION, RENDERER_CONTEXT_MINOR);

        if (SDL_RecreateWindow(window, window_flags | SDL_WINDOW_OPENGL) < 0) {
            goto error;
        }
    }

    /* Create the renderer struct */
    renderer = (SDL_Renderer *)SDL_calloc(1, sizeof(SDL_Renderer));
    if (!renderer) {
        SDL_OutOfMemory();
        goto error;
    }

    data = (GLES2_DriverContext *)SDL_calloc(1, sizeof(GLES2_DriverContext));
    if (!data) {
        GLES2_DestroyRenderer(renderer);
        SDL_OutOfMemory();
        goto error;
    }
    renderer->info = GLES2_RenderDriver.info;
    renderer->info.flags = (SDL_RENDERER_ACCELERATED | SDL_RENDERER_TARGETTEXTURE);
    renderer->driverdata = data;
    renderer->window = window;

    /* Create an OpenGL ES 2.0 context */
    data->context = SDL_GL_CreateContext(window);
    if (!data->context) {
        GLES2_DestroyRenderer(renderer);
        goto error;
    }
    if (SDL_GL_MakeCurrent(window, data->context) < 0) {
        GLES2_DestroyRenderer(renderer);
        goto error;
    }

    if (GLES2_LoadFunctions(data) < 0) {
        GLES2_DestroyRenderer(renderer);
        goto error;
    }

#if __WINRT__
    /* DLudwig, 2013-11-29: ANGLE for WinRT doesn't seem to work unless VSync
     * is turned on.  Not doing so will freeze the screen's contents to that
     * of the first drawn frame.
     */
    flags |= SDL_RENDERER_PRESENTVSYNC;
#endif

    if (flags & SDL_RENDERER_PRESENTVSYNC) {
        SDL_GL_SetSwapInterval(1);
    } else {
        SDL_GL_SetSwapInterval(0);
    }
    if (SDL_GL_GetSwapInterval() > 0) {
        renderer->info.flags |= SDL_RENDERER_PRESENTVSYNC;
    }

    /* Check for debug output support */
    if (SDL_GL_GetAttribute(SDL_GL_CONTEXT_FLAGS, &value) == 0 &&
        (value & SDL_GL_CONTEXT_DEBUG_FLAG)) {
        data->debug_enabled = SDL_TRUE;
    }

    value = 0;
    data->glGetIntegerv(GL_MAX_TEXTURE_SIZE, &value);
    renderer->info.max_texture_width = value;
    value = 0;
    data->glGetIntegerv(GL_MAX_TEXTURE_SIZE, &value);
    renderer->info.max_texture_height = value;

    /* Determine supported shader formats */
    /* HACK: glGetInteger is broken on the Zune HD's compositor, so we just hardcode this */
#ifdef ZUNE_HD
    nFormats = 1;
#else /* !ZUNE_HD */
    data->glGetIntegerv(GL_NUM_SHADER_BINARY_FORMATS, &nFormats);
    data->glGetBooleanv(GL_SHADER_COMPILER, &hasCompiler);
    if (hasCompiler) {
        ++nFormats;
    }
#endif /* ZUNE_HD */
    data->shader_formats = (GLenum *)SDL_calloc(nFormats, sizeof(GLenum));
    if (!data->shader_formats) {
        GLES2_DestroyRenderer(renderer);
        SDL_OutOfMemory();
        goto error;
    }
    data->shader_format_count = nFormats;
#ifdef ZUNE_HD
    data->shader_formats[0] = GL_NVIDIA_PLATFORM_BINARY_NV;
#else /* !ZUNE_HD */
    data->glGetIntegerv(GL_SHADER_BINARY_FORMATS, (GLint *)data->shader_formats);
    if (hasCompiler) {
        data->shader_formats[nFormats - 1] = (GLenum)-1;
    }
#endif /* ZUNE_HD */

    data->framebuffers = NULL;
    data->glGetIntegerv(GL_FRAMEBUFFER_BINDING, &window_framebuffer);
    data->window_framebuffer = (GLuint)window_framebuffer;

    /* Populate the function pointers for the module */
    renderer->WindowEvent         = GLES2_WindowEvent;
    renderer->GetOutputSize       = GLES2_GetOutputSize;
    renderer->SupportsBlendMode   = GLES2_SupportsBlendMode;
    renderer->CreateTexture       = GLES2_CreateTexture;
    renderer->UpdateTexture       = GLES2_UpdateTexture;
    renderer->UpdateTextureYUV    = GLES2_UpdateTextureYUV;
    renderer->LockTexture         = GLES2_LockTexture;
    renderer->UnlockTexture       = GLES2_UnlockTexture;
    renderer->SetRenderTarget     = GLES2_SetRenderTarget;
    renderer->UpdateViewport      = GLES2_UpdateViewport;
    renderer->UpdateClipRect      = GLES2_UpdateClipRect;
    renderer->RenderClear         = GLES2_RenderClear;
    renderer->RenderDrawPoints    = GLES2_RenderDrawPoints;
    renderer->RenderDrawLines     = GLES2_RenderDrawLines;
    renderer->RenderFillRects     = GLES2_RenderFillRects;
    renderer->RenderCopy          = GLES2_RenderCopy;
    renderer->RenderCopyEx        = GLES2_RenderCopyEx;
    renderer->RenderReadPixels    = GLES2_RenderReadPixels;
    renderer->RenderPresent       = GLES2_RenderPresent;
    renderer->DestroyTexture      = GLES2_DestroyTexture;
    renderer->DestroyRenderer     = GLES2_DestroyRenderer;
    renderer->GL_BindTexture      = GLES2_BindTexture;
    renderer->GL_UnbindTexture    = GLES2_UnbindTexture;

    renderer->info.texture_formats[renderer->info.num_texture_formats++] = SDL_PIXELFORMAT_YV12;
    renderer->info.texture_formats[renderer->info.num_texture_formats++] = SDL_PIXELFORMAT_IYUV;
    renderer->info.texture_formats[renderer->info.num_texture_formats++] = SDL_PIXELFORMAT_NV12;
    renderer->info.texture_formats[renderer->info.num_texture_formats++] = SDL_PIXELFORMAT_NV21;
#ifdef GL_TEXTURE_EXTERNAL_OES
    renderer->info.texture_formats[renderer->info.num_texture_formats++] = SDL_PIXELFORMAT_EXTERNAL_OES;
#endif

    GLES2_ResetState(renderer);

    return renderer;

error:
    if (changed_window) {
        /* Uh oh, better try to put it back... */
        SDL_GL_SetAttribute(SDL_GL_CONTEXT_PROFILE_MASK, profile_mask);
        SDL_GL_SetAttribute(SDL_GL_CONTEXT_MAJOR_VERSION, major);
        SDL_GL_SetAttribute(SDL_GL_CONTEXT_MINOR_VERSION, minor);
        SDL_RecreateWindow(window, window_flags);
    }
    return NULL;
}

#endif /* SDL_VIDEO_RENDER_OGL_ES2 && !SDL_RENDER_DISABLED */

经过一系列对window flag的判断，最终走到了创建GLContext 和 MakeCurrent 上
GLES2_LoadFunctions

接着设置刷新率
SDL_GL_SetSwapInterval 如果是跟着设备的v ysn同步信号的话，就是1 否则是0

最后将各种renderer中的各种gl方法，进行初始化。
GLES2_CreateTexture 方法，是创建纹理的方法，可以看到,确实是熟悉的问题，创建纹理的过程。不同的是，如果是yuv就会创建3个纹理 。

static int
GLES2_CreateTexture(SDL_Renderer *renderer, SDL_Texture *texture)
{
    GLES2_DriverContext *renderdata = (GLES2_DriverContext *)renderer->driverdata;
    GLES2_TextureData *data;
    GLenum format;
    GLenum type;
    GLenum scaleMode;

    GLES2_ActivateRenderer(renderer);

    /* Determine the corresponding GLES texture format params */
    switch (texture->format)
    {
    case SDL_PIXELFORMAT_ARGB8888:
    case SDL_PIXELFORMAT_ABGR8888:
    case SDL_PIXELFORMAT_RGB888:
    case SDL_PIXELFORMAT_BGR888:
        format = GL_RGBA;
        type = GL_UNSIGNED_BYTE;
        break;
    case SDL_PIXELFORMAT_IYUV:
    case SDL_PIXELFORMAT_YV12:
    case SDL_PIXELFORMAT_NV12:
    case SDL_PIXELFORMAT_NV21:
        format = GL_LUMINANCE;
        type = GL_UNSIGNED_BYTE;
        break;
#ifdef GL_TEXTURE_EXTERNAL_OES
    case SDL_PIXELFORMAT_EXTERNAL_OES:
        format = GL_NONE;
        type = GL_NONE;
        break;
#endif
    default:
        return SDL_SetError("Texture format not supported");
    }

    if (texture->format == SDL_PIXELFORMAT_EXTERNAL_OES &&
        texture->access != SDL_TEXTUREACCESS_STATIC) {
        return SDL_SetError("Unsupported texture access for SDL_PIXELFORMAT_EXTERNAL_OES");
    }

    /* Allocate a texture struct */
    data = (GLES2_TextureData *)SDL_calloc(1, sizeof(GLES2_TextureData));
    if (!data) {
        return SDL_OutOfMemory();
    }
    data->texture = 0;
#ifdef GL_TEXTURE_EXTERNAL_OES
    data->texture_type = (texture->format == SDL_PIXELFORMAT_EXTERNAL_OES) ? GL_TEXTURE_EXTERNAL_OES : GL_TEXTURE_2D;
#else
    data->texture_type = GL_TEXTURE_2D;
#endif
    data->pixel_format = format;
    data->pixel_type = type;
    data->yuv = ((texture->format == SDL_PIXELFORMAT_IYUV) || (texture->format == SDL_PIXELFORMAT_YV12));
    data->nv12 = ((texture->format == SDL_PIXELFORMAT_NV12) || (texture->format == SDL_PIXELFORMAT_NV21));
    data->texture_u = 0;
    data->texture_v = 0;
    scaleMode = (texture->scaleMode == SDL_ScaleModeNearest) ? GL_NEAREST : GL_LINEAR;

    /* Allocate a blob for image renderdata */
    if (texture->access == SDL_TEXTUREACCESS_STREAMING) {
        size_t size;
        data->pitch = texture->w * SDL_BYTESPERPIXEL(texture->format);
        size = texture->h * data->pitch;
        if (data->yuv) {
            /* Need to add size for the U and V planes */
            size += 2 * ((texture->h + 1) / 2) * ((data->pitch + 1) / 2);
        }
        if (data->nv12) {
            /* Need to add size for the U/V plane */
            size += 2 * ((texture->h + 1) / 2) * ((data->pitch + 1) / 2);
        }
        data->pixel_data = SDL_calloc(1, size);
        if (!data->pixel_data) {
            SDL_free(data);
            return SDL_OutOfMemory();
        }
    }

    /* Allocate the texture */
    GL_CheckError("", renderer);

    if (data->yuv) {
        renderdata->glGenTextures(1, &data->texture_v);
        if (GL_CheckError("glGenTexures()", renderer) < 0) {
            return -1;
        }
        renderdata->glActiveTexture(GL_TEXTURE2);
        renderdata->glBindTexture(data->texture_type, data->texture_v);
        renderdata->glTexParameteri(data->texture_type, GL_TEXTURE_MIN_FILTER, scaleMode);
        renderdata->glTexParameteri(data->texture_type, GL_TEXTURE_MAG_FILTER, scaleMode);
        renderdata->glTexParameteri(data->texture_type, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
        renderdata->glTexParameteri(data->texture_type, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
        renderdata->glTexImage2D(data->texture_type, 0, format, (texture->w + 1) / 2, (texture->h + 1) / 2, 0, format, type, NULL);

        renderdata->glGenTextures(1, &data->texture_u);
        if (GL_CheckError("glGenTexures()", renderer) < 0) {
            return -1;
        }
        renderdata->glActiveTexture(GL_TEXTURE1);
        renderdata->glBindTexture(data->texture_type, data->texture_u);
        renderdata->glTexParameteri(data->texture_type, GL_TEXTURE_MIN_FILTER, scaleMode);
        renderdata->glTexParameteri(data->texture_type, GL_TEXTURE_MAG_FILTER, scaleMode);
        renderdata->glTexParameteri(data->texture_type, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
        renderdata->glTexParameteri(data->texture_type, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
        renderdata->glTexImage2D(data->texture_type, 0, format, (texture->w + 1) / 2, (texture->h + 1) / 2, 0, format, type, NULL);
        if (GL_CheckError("glTexImage2D()", renderer) < 0) {
            return -1;
        }
    }

    if (data->nv12) {
        renderdata->glGenTextures(1, &data->texture_u);
        if (GL_CheckError("glGenTexures()", renderer) < 0) {
            return -1;
        }
        renderdata->glActiveTexture(GL_TEXTURE1);
        renderdata->glBindTexture(data->texture_type, data->texture_u);
        renderdata->glTexParameteri(data->texture_type, GL_TEXTURE_MIN_FILTER, scaleMode);
        renderdata->glTexParameteri(data->texture_type, GL_TEXTURE_MAG_FILTER, scaleMode);
        renderdata->glTexParameteri(data->texture_type, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
        renderdata->glTexParameteri(data->texture_type, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
        renderdata->glTexImage2D(data->texture_type, 0, GL_LUMINANCE_ALPHA, (texture->w + 1) / 2, (texture->h + 1) / 2, 0, GL_LUMINANCE_ALPHA, GL_UNSIGNED_BYTE, NULL);
        if (GL_CheckError("glTexImage2D()", renderer) < 0) {
            return -1;
        }
    }

    renderdata->glGenTextures(1, &data->texture);
    if (GL_CheckError("glGenTexures()", renderer) < 0) {
        return -1;
    }
    texture->driverdata = data;
    renderdata->glActiveTexture(GL_TEXTURE0);
    renderdata->glBindTexture(data->texture_type, data->texture);
    renderdata->glTexParameteri(data->texture_type, GL_TEXTURE_MIN_FILTER, scaleMode);
    renderdata->glTexParameteri(data->texture_type, GL_TEXTURE_MAG_FILTER, scaleMode);
    renderdata->glTexParameteri(data->texture_type, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
    renderdata->glTexParameteri(data->texture_type, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
    if (texture->format != SDL_PIXELFORMAT_EXTERNAL_OES) {
        renderdata->glTexImage2D(data->texture_type, 0, format, texture->w, texture->h, 0, format, type, NULL);
        if (GL_CheckError("glTexImage2D()", renderer) < 0) {
            return -1;
        }
    }

    if (texture->access == SDL_TEXTUREACCESS_TARGET) {
       data->fbo = GLES2_GetFBO(renderer->driverdata, texture->w, texture->h);
    } else {
       data->fbo = NULL;
    }

    return GL_CheckError("", renderer);
}

update

static int
GLES2_UpdateTexture(SDL_Renderer *renderer, SDL_Texture *texture, const SDL_Rect *rect,
                    const void *pixels, int pitch)
{
    GLES2_DriverContext *data = (GLES2_DriverContext *)renderer->driverdata;
    GLES2_TextureData *tdata = (GLES2_TextureData *)texture->driverdata;

    GLES2_ActivateRenderer(renderer);

    /* Bail out if we're supposed to update an empty rectangle */
    if (rect->w <= 0 || rect->h <= 0) {
        return 0;
    }

    /* Create a texture subimage with the supplied data */
    data->glBindTexture(tdata->texture_type, tdata->texture);
    GLES2_TexSubImage2D(data, tdata->texture_type,
                    rect->x,
                    rect->y,
                    rect->w,
                    rect->h,
                    tdata->pixel_format,
                    tdata->pixel_type,
                    pixels, pitch, SDL_BYTESPERPIXEL(texture->format));

    if (tdata->yuv) {
        /* Skip to the correct offset into the next texture */
        pixels = (const void*)((const Uint8*)pixels + rect->h * pitch);
        if (texture->format == SDL_PIXELFORMAT_YV12) {
            data->glBindTexture(tdata->texture_type, tdata->texture_v);
        } else {
            data->glBindTexture(tdata->texture_type, tdata->texture_u);
        }
        GLES2_TexSubImage2D(data, tdata->texture_type,
                rect->x / 2,
                rect->y / 2,
                (rect->w + 1) / 2,
                (rect->h + 1) / 2,
                tdata->pixel_format,
                tdata->pixel_type,
                pixels, (pitch + 1) / 2, 1);


        /* Skip to the correct offset into the next texture */
        pixels = (const void*)((const Uint8*)pixels + ((rect->h + 1) / 2) * ((pitch + 1)/2));
        if (texture->format == SDL_PIXELFORMAT_YV12) {
            data->glBindTexture(tdata->texture_type, tdata->texture_u);
        } else {
            data->glBindTexture(tdata->texture_type, tdata->texture_v);
        }
        GLES2_TexSubImage2D(data, tdata->texture_type,
                rect->x / 2,
                rect->y / 2,
                (rect->w + 1) / 2,
                (rect->h + 1) / 2,
                tdata->pixel_format,
                tdata->pixel_type,
                pixels, (pitch + 1) / 2, 1);
    }

    if (tdata->nv12) {
        /* Skip to the correct offset into the next texture */
        pixels = (const void*)((const Uint8*)pixels + rect->h * pitch);
        data->glBindTexture(tdata->texture_type, tdata->texture_u);
        GLES2_TexSubImage2D(data, tdata->texture_type,
                rect->x / 2,
                rect->y / 2,
                (rect->w + 1) / 2,
                (rect->h + 1) / 2,
                GL_LUMINANCE_ALPHA,
                GL_UNSIGNED_BYTE,
                pixels, 2 * ((pitch + 1) / 2), 2);
    }

    return GL_CheckError("glTexSubImage2D()", renderer);
}

GLES2_TexSubImage2D 方法

static int
GLES2_TexSubImage2D(GLES2_DriverContext *data, GLenum target, GLint xoffset, GLint yoffset, GLsizei width, GLsizei height, GLenum format, GLenum type, const GLvoid *pixels, GLint pitch, GLint bpp)
{
    Uint8 *blob = NULL;
    Uint8 *src;
    int src_pitch;
    int y;

    if ((width == 0) || (height == 0) || (bpp == 0)) {
        return 0;  /* nothing to do */
    }

    /* Reformat the texture data into a tightly packed array */
    src_pitch = width * bpp;
    src = (Uint8 *)pixels;
    if (pitch != src_pitch) {
        blob = (Uint8 *)SDL_malloc(src_pitch * height);
        if (!blob) {
            return SDL_OutOfMemory();
        }
        src = blob;
        for (y = 0; y < height; ++y)
        {
            SDL_memcpy(src, pixels, src_pitch);
            src += src_pitch;
            pixels = (Uint8 *)pixels + pitch;
        }
        src = blob;
    }

    data->glTexSubImage2D(target, 0, xoffset, yoffset, width, height, format, type, src);
    if (blob) {
        SDL_free(blob);
    }
    return 0;
}

GLES2_UpdateTextureYUV 方法中，就是减少了判断。

SDL_RenderCopy 方法会将render 中的参数，使用texture来进行绘制。
GLES2_SetupCopy-》GLES2_SelectProgram

这个过程中，会进行创建Shader Fragment着色器，创建program 来进行使用。
同时绑定纹理，坐标系和blendMode 做好绘制的准备

GLES2_RenderReadPixels 读取像素

GLES2_RenderPresent 调用Swap方法 SwapBuffers

4. 纹理SDL_Texture

   
   
   image.png

/**
 *  \brief Create a texture for a rendering context.
 *
 *  \param renderer The renderer.
 *  \param format The format of the texture.
 *  \param access One of the enumerated values in ::SDL_TextureAccess.
 *  \param w      The width of the texture in pixels.
 *  \param h      The height of the texture in pixels.
 *
 *  \return The created texture is returned, or NULL if no rendering context was
 *          active,  the format was unsupported, or the width or height were out
 *          of range.
 *
 *  \note The contents of the texture are not defined at creation.
 *
 *  \sa SDL_QueryTexture()
 *  \sa SDL_UpdateTexture()
 *  \sa SDL_DestroyTexture()
 */

SDL循环渲染数据

update_circle.png

总结

image.png

参考

雷神SDL2源代码分析系列