安卓如何texture预览相机

在Android平台上，您可以使用Camera2 API来获取相机预览并将其渲染到texture上。以下是一些大致的步骤：

1. 在AndroidManifest.xml文件中添加相机权限：

<uses-permission android:name="android.permission.CAMERA" />

2. 在布局文件中添加一个TextureView元素，用于显示相机预览：

<TextureView
    android:id="@+id/texture_view"
    android:layout_width="match_parent"
    android:layout_height="match_parent" />

3. 在Activity中获取TextureView并设置SurfaceTextureListener：

public class MainActivity extends AppCompatActivity implements TextureView.SurfaceTextureListener {

    private TextureView mTextureView;
    private CameraDevice mCameraDevice;
    private CameraCaptureSession mCaptureSession;
    private CaptureRequest.Builder mPreviewRequestBuilder;
    private CaptureRequest mPreviewRequest;

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

        mTextureView = findViewById(R.id.texture_view);
        mTextureView.setSurfaceTextureListener(this);
    }

    @Override
    public void onSurfaceTextureAvailable(SurfaceTexture surface, int width, int height) {
        // 在SurfaceTexture准备好后打开相机
        openCamera();
    }

    @Override
    public void onSurfaceTextureSizeChanged(SurfaceTexture surface, int width, int height) {
        // SurfaceTexture尺寸发生变化时更新预览尺寸
        updatePreview();
    }

    @Override
    public boolean onSurfaceTextureDestroyed(SurfaceTexture surface) {
        // 释放相机资源
        closeCamera();
        return true;
    }

    @Override
    public void onSurfaceTextureUpdated(SurfaceTexture surface) {
        // SurfaceTexture更新时的回调
    }

    private void openCamera() {
        // 获取相机服务
        CameraManager manager = (CameraManager) getSystemService(Context.CAMERA_SERVICE);
        try {
            // 获取可用相机列表
            String cameraId = manager.getCameraIdList()[0];

            // 获取相机特性
            CameraCharacteristics characteristics = manager.getCameraCharacteristics(cameraId);

            // 检查是否支持相机预览
            int[] capabilities = characteristics.get(CameraCharacteristics.REQUEST_AVAILABLE_CAPABILITIES);
            if (capabilities == null || capabilities.length == 0
                    || capabilities[0] != CameraCharacteristics.REQUEST_AVAILABLE_CAPABILITIES_BACKWARD_COMPATIBLE) {
                // 不支持相机预览，退出
                return;
            }

            // 获取相机尺寸
            StreamConfigurationMap map = characteristics.get(CameraCharacteristics.SCALER_STREAM_CONFIGURATION_MAP);
            Size[] sizes = map.getOutputSizes(SurfaceTexture.class);
            Size previewSize = sizes[0];

            // 打开相机
            manager.openCamera(cameraId, new CameraDevice.StateCallback() {
                @Override
                public void onOpened(@NonNull CameraDevice camera) {
                    // 相机打开后的回调，保存相机Device实例
                    mCameraDevice = camera;
                    // 创建相机预览
                    createPreview();
                }

                @Override
                public void onDisconnected(@NonNull CameraDevice camera) {
                    // 相机断开连接后的回调
                    closeCamera();
                }

                @Override
                public void onError(@NonNull CameraDevice camera, int error) {
                    // 相机错误后的回调
                    closeCamera();
                }
            }, null);

        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    private void closeCamera() {
        // 关闭相机资源
        if (mCaptureSession != null) {
            mCaptureSession.close();
            mCaptureSession = null;
        }
        if (mCameraDevice != null) {
            mCameraDevice.close();
            mCameraDevice = null;
        }
    }

    private void createPreview() {
        try {
            // 创建SurfaceTexture
            SurfaceTexture texture = mTextureView.getSurfaceTexture();
            // 设置默认缓冲区大小
            texture.setDefaultBufferSize(mTextureView.getWidth(), mTextureView.getHeight());
            // 创建Surface
            Surface surface = new Surface(texture);

            // 创建预览请求
            mPreviewRequestBuilder = mCameraDevice.createCaptureRequest(CameraDevice.TEMPLATE_PREVIEW);
            mPreviewRequestBuilder.addTarget(surface);
            mPreviewRequest = mPreviewRequestBuilder.build();

            // 创建相机会话
            mCameraDevice.createCaptureSession(Arrays.asList(surface), new CameraCaptureSession.StateCallback() {
                @Override
                public void onConfigured(@NonNull CameraCaptureSession session) {
                    // 会话配置完成后开始预览
                    mCaptureSession = session;
                    try {
                        mCaptureSession.setRepeatingRequest(mPreviewRequest, null, null);
                    } catch (Exception e) {
                        e.printStackTrace();
                    }
                }

                @Override
                public void onConfigureFailed(@NonNull CameraCaptureSession session) {
                    // 配置会话失败
                }
            }, null);

        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    private void updatePreview() {
        // 更新预览尺寸
        if (mPreviewRequestBuilder != null) {
            try {
                // 获取相机特性
                CameraManager manager = (CameraManager) getSystemService(Context.CAMERA_SERVICE);
                String cameraId = manager.getCameraIdList()[0];
                CameraCharacteristics characteristics = manager.getCameraCharacteristics(cameraId);

                // 获取相机尺寸
                StreamConfigurationMap map = characteristics.get(CameraCharacteristics.SCALER_STREAM_CONFIGURATION_MAP);
                Size[] sizes = map.getOutputSizes(SurfaceTexture.class);
                Size previewSize = sizes[0];

                // 更新预览请求
                SurfaceTexture texture = mTextureView.getSurfaceTexture();
                texture.setDefaultBufferSize(previewSize.getWidth(), previewSize.getHeight());
                Surface surface = new Surface(texture);
                mPreviewRequestBuilder.addTarget(surface);
                mPreviewRequest = mPreviewRequestBuilder.build();
                mCaptureSession.setRepeatingRequest(mPreviewRequest, null, null);

            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    }
}

以上代码中，`onSurfaceTextureAvailable`回调中打开相机，`onSurfaceTextureSizeChanged`回调中更新预览尺寸，`onSurfaceTextureDestroyed`回调中释放相机资源。`createPreview`方法用于创建相机预览，`updatePreview`方法用于更新预览尺寸。请注意，在Android平台上使用相机需要处理许多异常情况，上述代码仅供参考。