1、AnativeWindow 官方解釋為：

• ANativeWindow represents the producer end of an image queue.
• It is the C counterpart of the android.view.Surface object in Java,
• and can be converted both ways. Depending on the consumer, images
• submitted to ANativeWindow can be shown on the display or sent to
• other consumers, such as video encoders.
  谷歌翻譯：ANativeWindow表示圖像隊(duì)列的生產(chǎn)者端。它是Java中android.view.Surface對(duì)象的C對(duì)應(yīng)物，并且可以雙向轉(zhuǎn)換。 取決于消費(fèi)者，提交到ANativeWindow的圖像可以顯示在顯示器上或發(fā)送給其他消費(fèi)者，例如視頻編碼器。
  因此可以理解的是 Java中可以提供一個(gè)surface通過NDK的方式利用AnativeWindow的API實(shí)現(xiàn)圖像的繪制。
  2、常規(guī)的相機(jī)數(shù)據(jù)處理并顯示的方案：
  ①、利用OpenGL ES 中的shader語(yǔ)言對(duì)圖像進(jìn)行處理；（高效也推薦這個(gè)方法）
  ②、將camera的數(shù)據(jù)傳到底層 進(jìn)行識(shí)別，上層再利用cavans或者其它去繪制我們想表達(dá)的東西，例如：框框、文字等。
  ③、利用AnativeWindow API去實(shí)現(xiàn)相機(jī)圖像數(shù)據(jù)的處理，這種做法存在一定的局限性，對(duì)于一些本身處理比較復(fù)雜的算法，圖像的顯示和繪制會(huì)極為的卡頓。但是AnativeWindow常常用于Video的顯示，算是Android多媒體中一個(gè)比較有用的API。
  3、AnativeWindow顯示流程：
  ①、Camera2 通過ImageReader方式得到相機(jī)data；
  ②、將所得到的Yuvdata通過JNI傳到native層；
  ③、native中將Yuvdata進(jìn)行解碼轉(zhuǎn)成AnativeWindow可以用來繪制的圖像格式；
  AnativeWindow所支持的圖像數(shù)據(jù)格式：

enum ANativeWindow_LegacyFormat {
    // NOTE: these values must match the values from graphics/common/x.x/types.hal

    /** Red: 8 bits, Green: 8 bits, Blue: 8 bits, Alpha: 8 bits. **/
    WINDOW_FORMAT_RGBA_8888          = AHARDWAREBUFFER_FORMAT_R8G8B8A8_UNORM,
    /** Red: 8 bits, Green: 8 bits, Blue: 8 bits, Unused: 8 bits. **/
    WINDOW_FORMAT_RGBX_8888          = AHARDWAREBUFFER_FORMAT_R8G8B8X8_UNORM,
    /** Red: 5 bits, Green: 6 bits, Blue: 5 bits. **/
    WINDOW_FORMAT_RGB_565            = AHARDWAREBUFFER_FORMAT_R5G6B5_UNORM,
};

4、關(guān)鍵代碼
Java：

private ImageReader.OnImageAvailableListener mOnImageAvailableListener = new ImageReader.OnImageAvailableListener() {

        /*
         *  The following method will be called every time an image is ready
         *  be sure to use method acquireNextImage() and then close(), otherwise, the display may STOP
         */
        @Override
        public void onImageAvailable(ImageReader reader) {
            // get the newest frame
            Image image = reader.acquireNextImage();

            if (image == null) {
                return;
            }
            final byte[] yuvdata=ImageUtil.getBytesFromImageAsType(image,0);
            draw(image.getWidth(),image.getHeight(),yuvdata,surface);
            Log.d("pctest","yuvdata length:"+yuvdata.length+"image height:"+image.getHeight()+"image width"+image.getWidth());
            image.close();
        }
    };

private void startPreview(CameraDevice mCamera) throws CameraAccessException {
        SurfaceTexture texture = mPreviewView.getSurfaceTexture();
        texture.setDefaultBufferSize(mPreviewSize.getWidth(),mPreviewSize.getHeight());
        surface = new Surface(texture);
        try {
            // to set request for PREVIEW
            mPreviewBuilder = mCamera.createCaptureRequest(CameraDevice.TEMPLATE_PREVIEW);
        } catch (CameraAccessException e) {
            e.printStackTrace();
        }
        mImageReader = ImageReader.newInstance(mImageWidth,mImageHeight, ImageFormat.YUV_420_888,2);
        mImageReader.setOnImageAvailableListener(mOnImageAvailableListener,mHandler);
        mPreviewBuilder.addTarget(mImageReader.getSurface());
        List<Surface> outputSurfaces = new ArrayList<>();
        outputSurfaces.add(mImageReader.getSurface());
        mCamera.createCaptureSession(outputSurfaces, mSessionStateCallback, mHandler);
    }

Native:
在對(duì)數(shù)據(jù)處理中利用的 OpenCV 進(jìn)行圖像數(shù)據(jù)轉(zhuǎn)碼，只是為了方便= 。=（PS：轉(zhuǎn)碼這是太。。。）

extern "C"
JNIEXPORT void JNICALL
Java_com_example_anativewindow4camera2_MainActivity_draw(JNIEnv *env, jobject thiz, jint width,
                                                         jint height, jbyteArray yuvdata,
                                                         jobject surface) {
    // TODO: implement draw()
    jbyte *data = env->GetByteArrayElements(yuvdata, NULL);
    Mat src(height + height / 2, width, CV_8UC1, data);
    cvtColor(src, src, COLOR_YUV2RGBA_IYUV);
    cv::transpose(src,src);
    cv::flip(src,src,1);
    ANativeWindow * window = ANativeWindow_fromSurface(env, surface);
    ANativeWindow_acquire(window);
    ANativeWindow_Buffer buffer;
    ANativeWindow_setBuffersGeometry(window, src.cols, src.rows, WINDOW_FORMAT_RGBA_8888);
    if (int32_t err = ANativeWindow_lock(window, &buffer, NULL)) {
        LOGE("ANativeWindow_lock failed with error code: %d\n", err);
        ANativeWindow_release(window);
    }
    uint8_t * outPtr = reinterpret_cast<uint8_t *>(buffer.bits);
    int dst_line_size = buffer.stride * 4;
    //一行一行拷貝
    for (int i = 0; i < buffer.height; ++i) {
        //void *memcpy(void *dest, const void *src, size_t n);
        //從源src所指的內(nèi)存地址的起始位置開始拷貝n個(gè)字節(jié)到目標(biāo)dest所指的內(nèi)存地址的起始位置中
        memcpy(outPtr + i * dst_line_size,
               src.data + i * src.cols * 4, dst_line_size);
    }

    ANativeWindow_unlockAndPost(window);
    ANativeWindow_release(window);
    src.release();
    env->ReleaseByteArrayElements(yuvdata, data, 0);
}

5、記錄一下，怕后面忘了。。。