Android Camera2相机预览画面手勢放大缩小

在Android中使用Camera2 API实现相机预览画面的手勢放大缩小功能，可以通过以下步骤实现：

1. **初始化Camera2 API**：首先，需要初始化Camera2 API并启动预览。

2. **设置触摸监听器**：在预览界面上设置触摸监听器，检测用户的缩放手势。

3. **计算缩放因子**：根据用户的缩放手势计算缩放因子。

4. **更新相机预览**：根据缩放因子更新相机的预览比例。

以下是一个简单的示例代码，展示了如何实现上述步骤：

public class CameraActivity extends AppCompatActivity {

    private TextureView textureView;
    private CameraDevice cameraDevice;
    private CameraCaptureSession captureSession;
    private CaptureRequest.Builder captureRequestBuilder;
    private float currentZoomLevel = 1.0f;

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

        textureView = findViewById(R.id.textureView);
        textureView.setSurfaceTextureListener(textureListener);
    }

    TextureView.SurfaceTextureListener textureListener = new TextureView.SurfaceTextureListener() {
        @Override
        public void onSurfaceTextureAvailable(SurfaceTexture surface, int width, int height) {
            openCamera();
        }

        @Override
        public void onSurfaceTextureSizeChanged(SurfaceTexture surface, int width, int height) {
            // 处理预览界面的尺寸变化
        }

        @Override
        public boolean onSurfaceTextureDestroyed(SurfaceTexture surface) {
            return false;
        }

        @Override
        public void onSurfaceTextureUpdated(SurfaceTexture surface) {
            // 更新预览界面
        }
    };

    private void openCamera() {
        CameraManager manager = (CameraManager) getSystemService(Context.CAMERA_SERVICE);
        try {
            String cameraId = manager.getCameraIdList()[0];
            CameraCharacteristics characteristics = manager.getCameraCharacteristics(cameraId);
            StreamConfigurationMap map = characteristics.get(CameraCharacteristics.SCALER_STREAM_CONFIGURATION_MAP);
            // 打开相机
            manager.openCamera(cameraId, stateCallback, null);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    private CameraDevice.StateCallback stateCallback = new CameraDevice.StateCallback() {
        @Override
        public void onOpened(CameraDevice camera) {
            cameraDevice = camera;
            createCameraPreview();
        }

        @Override
        public void onDisconnected(CameraDevice camera) {
            cameraDevice.close();
        }

        @Override
        public void onError(CameraDevice camera, int error) {
            cameraDevice.close();
            cameraDevice = null;
        }
    };

    protected void createCameraPreview() {
        try {
            SurfaceTexture texture = textureView.getSurfaceTexture();
            assert texture != null;
            texture.setDefaultBufferSize(1920, 1080);
            Surface surface = new Surface(texture);
            captureRequestBuilder = cameraDevice.createCaptureRequest(CameraDevice.TEMPLATE_PREVIEW);
            captureRequestBuilder.addTarget(surface);
            cameraDevice.createCaptureSession(Arrays.asList(surface), new CameraCaptureSession.StateCallback() {
                @Override
                public void onConfigured(CameraCaptureSession session) {
                    if (cameraDevice == null) return;
                    captureSession = session;
                    updatePreview();
                }

                @Override
                public void onConfigureFailed(CameraCaptureSession session) {
                    // 处理配置失败
                }
            }, null);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    protected void updatePreview() {
        if (cameraDevice == null) return;
        captureRequestBuilder.set(CaptureRequest.CONTROL_MODE, CameraMetadata.CONTROL_MODE_AUTO);
        try {
            captureSession.setRepeatingRequest(captureRequestBuilder.build(), null, null);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        switch (event.getAction() & MotionEvent.ACTION_MASK) {
            case MotionEvent.ACTION_POINTER_DOWN:
                break;
            case MotionEvent.ACTION_MOVE:
                if (event.getPointerCount() == 2) {
                    float newDist = getFingerSpacing(event);
                    handleZoom(newDist);
                }
                break;
        }
        return super.onTouchEvent(event);
    }

    private float getFingerSpacing(MotionEvent event) {
        float x = event.getX(0) - event.getX(1);
        float y = event.getY(0) - event.getY(1);
        return (float) Math.sqrt(x * x + y * y);
    }

    private void handleZoom(float newDist) {
        float delta = newDist - previousDist;
        if (delta > 0) {
            currentZoomLevel += 0.1f;
        } else {
            currentZoomLevel -= 0.1f;
        }
        currentZoomLevel = Math.max(1.0f, Math.min(currentZoomLevel, maxZoomLevel));
        captureRequestBuilder.set(CaptureRequest.SCALER_CROP_REGION, calculateZoomRect(currentZoomLevel));
        try {
            captureSession.setRepeatingRequest(captureRequestBuilder.build(), null, null);
        } catch (CameraAccessException e) {
            e.printStackTrace();
        }
        previousDist = newDist;
    }

    private Rect calculateZoomRect(float zoomLevel) {
        // 计算缩放区域
        return null;
    }
}