1、AnativeWindow 官方解释为：

• 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.
  谷歌翻译：ANativeWindow表示图像队列的生产者端。它是Java中android.view.Surface对象的C对应物，并且可以双向转换。 取决于消费者，提交到ANativeWindow的图像可以显示在显示器上或发送给其他消费者，例如视频编码器。
  因此可以理解的是 Java中可以提供一个surface通过NDK的方式利用AnativeWindow的API实现图像的绘制。
  2、常规的相机数据处理并显示的方案：
  ①、利用OpenGL ES 中的shader语言对图像进行处理；（高效也推荐这个方法）
  ②、将camera的数据传到底层 进行识别，上层再利用cavans或者其它去绘制我们想表达的东西，例如：框框、文字等。
  ③、利用AnativeWindow API去实现相机图像数据的处理，这种做法存在一定的局限性，对于一些本身处理比较复杂的算法，图像的显示和绘制会极为的卡顿。但是AnativeWindow常常用于Video的显示，算是Android多媒体中一个比较有用的API。
  3、AnativeWindow显示流程：
  ①、Camera2 通过ImageReader方式得到相机data；
  ②、将所得到的Yuvdata通过JNI传到native层；
  ③、native中将Yuvdata进行解码转成AnativeWindow可以用来绘制的图像格式；
  AnativeWindow所支持的图像数据格式：

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、关键代码
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:
在对数据处理中利用的 OpenCV 进行图像数据转码，只是为了方便= 。=（PS：转码这是太。。。）

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;
    //一行一行拷贝
    for (int i = 0; i < buffer.height; ++i) {
        //void *memcpy(void *dest, const void *src, size_t n);
        //从源src所指的内存地址的起始位置开始拷贝n个字节到目标dest所指的内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、记录一下，怕后面忘了。。。