cameraX在使用previewView时，如何为preview添加滤镜

要为 CameraX 的预览界面添加滤镜，需要使用 SurfaceTextureListener 接口来监听 CameraX 的预览界面 SurfaceTexture 的创建和销毁事件。在 SurfaceTexture 创建之后，可以将其转换为 Surface 对象，再将 Surface 对象传递给 MediaCodec 进行编码，实现预览界面滤镜的效果。

以下是一个使用 CameraX 和 OpenGL ES 滤镜库 Grafika 实现预览界面滤镜的示例代码：

public class CameraXActivity extends AppCompatActivity implements SurfaceTextureListener {

    private PreviewView mPreviewView;
    private CameraX.LensFacing mLensFacing = CameraX.LensFacing.BACK;
    private Executor mExecutor = Executors.newSingleThreadExecutor();

    private int mTextureId = -1;
    private EglCore mEglCore;
    private WindowSurface mWindowSurface;
    private Texture2dProgram mTextureProgram;
    private SurfaceTexture mSurfaceTexture;
    private Surface mSurface;

    @Override
    protected void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_camera_x);

        mPreviewView = findViewById(R.id.preview_view);
        mPreviewView.setSurfaceTextureListener(this);

        // 初始化 OpenGL ES 相关对象
        mEglCore = new EglCore(null, EglCore.FLAG_RECORDABLE);
        mTextureProgram = new Texture2dProgram(Texture2dProgram.ProgramType.TEXTURE_EXT);
        mTextureId = mTextureProgram.createTextureObject();

        // 启动 CameraX
        CameraX.bindToLifecycle(this, new Preview.Builder().build());
    }

    @Override
    public void onSurfaceTextureAvailable(SurfaceTexture surfaceTexture, int width, int height) {
        // 将 SurfaceTexture 转换为 Surface 对象
        mSurfaceTexture = surfaceTexture;
        mSurface = new Surface(surfaceTexture);

        // 创建 OpenGL ES 窗口
        mWindowSurface = new WindowSurface(mEglCore, mSurface, false);
        mWindowSurface.makeCurrent();

        // 设置预览界面滤镜
        mTextureProgram.setTextureSize(width, height);
        mTextureProgram.drawFrame(mTextureId, true);

        // 开始 CameraX 预览
        startPreview();
    }

    @Override
    public void onSurfaceTextureSizeChanged(SurfaceTexture surfaceTexture, int width, int height) {
        // 重新设置预览界面滤镜的尺寸
        mTextureProgram.setTextureSize(width, height);
    }

    @Override
    public boolean onSurfaceTextureDestroyed(SurfaceTexture surfaceTexture) {
        // 销毁 OpenGL ES 相关对象
        mWindowSurface.release();
        mTextureProgram.release();
        GLES20.glDeleteTextures(1, new int[] { mTextureId }, 0);
        mEglCore.release();

        // 停止 CameraX 预览
        stopPreview();

        return true;
    }

    @Override
    public void onSurfaceTextureUpdated(SurfaceTexture surfaceTexture) {
        // 实时更新预览界面滤镜
        mTextureProgram.drawFrame(mTextureId, true);
        mWindowSurface.swapBuffers();
    }

    private void startPreview() {
        ListenableFuture<ProcessCameraProvider> providerFuture = ProcessCameraProvider.getInstance(this);
        providerFuture.addListener(() -> {
            try {
                ProcessCameraProvider provider = providerFuture.get();
                Preview preview = new Preview.Builder().build();

                CameraSelector cameraSelector = new CameraSelector.Builder()
                        .requireLensFacing(mLensFacing)
                        .build();

                provider.unbindAll();
                provider.bindToLifecycle(this, cameraSelector, preview);

                preview.setSurfaceProvider(() -> mSurface);
            } catch (ExecutionException | InterruptedException e) {
                e.printStackTrace();
                Toast.makeText(CameraXActivity.this, "启动相机失败", Toast.LENGTH_SHORT).show();
            }
        }, mExecutor);
    }

    private void stopPreview() {
        ListenableFuture<ProcessCameraProvider> providerFuture = ProcessCameraProvider.getInstance(this);
        providerFuture.addListener(() -> {
            try {
                ProcessCameraProvider provider = providerFuture.get();
                provider.unbindAll();
            } catch (ExecutionException | InterruptedException e) {
                e.printStackTrace();
            }
        }, mExecutor);
    }
}

其中，Texture2dProgram 是 Grafika 中的一个 OpenGL ES 滤镜库，EglCore 封装了 EGL 的一些常用操作，WindowSurface 封装了 EGL 的窗口相关操作。在 SurfaceTextureListener 的回调方法中，使用 Texture2dProgram 将预览帧渲染到 OpenGL ES 窗口中，实现预览界面滤镜的效果。