Android 平台下基于AnativeWindow实现相机预览

2020-10-26 本文已影响0人码农小白two

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。。。

Android 平台下基于AnativeWindow实现相机预览

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