android SurfaceView 相机角度

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Android SurfaceView 相机角度

在Android开发中，有时候我们需要使用相机功能来进行拍照或录像。而当涉及到相机角度的问题时，我们需要考虑如何正确显示相机预览画面。本文将介绍如何在Android应用中使用SurfaceView来显示相机预览，并处理相机角度的调整。

使用SurfaceView显示相机预览

SurfaceView是Android中用于在屏幕上绘制2D图形和视频的控件，我们可以利用SurfaceView来显示相机预览。下面是一个简单的示例代码，演示如何使用SurfaceView来显示相机预览。

public class CameraPreview extends SurfaceView implements SurfaceHolder.Callback {
    private Camera mCamera;

    public CameraPreview(Context context, Camera camera) {
        super(context);
        mCamera = camera;

        // Install a SurfaceHolder.Callback so we get notified when the underlying surface is created and destroyed
        getHolder().addCallback(this);

        // Deprecated setting, but required on Android versions prior to 3.0
        getHolder().setType(SurfaceHolder.SURFACE_TYPE_PUSH_BUFFERS);
    }

    @Override
    public void surfaceCreated(SurfaceHolder holder) {
        // The Surface has been created, now tell the camera where to draw the preview
        try {
            mCamera.setPreviewDisplay(holder);
            mCamera.startPreview();
        } catch (IOException e) {
            Log.d(TAG, "Error setting camera preview: " + e.getMessage());
        }
    }

    @Override
    public void surfaceDestroyed(SurfaceHolder holder) {
        // Empty. Take care of releasing the Camera preview in your activity
    }

    @Override
    public void surfaceChanged(SurfaceHolder holder, int format, int w, int h) {
        // If your preview can change or rotate, take care of those events here
        if (getHolder().getSurface() == null){
            // preview surface does not exist
            return;
        }

        // Stop preview before making changes
        try {
            mCamera.stopPreview();
        } catch (Exception e){
            // ignore: tried to stop a non-existent preview
        }

        // Set preview size and make any resize, rotate or reformatting changes here

        // Start preview with new settings
        try {
            mCamera.setPreviewDisplay(holder);
            mCamera.startPreview();
        } catch (Exception e){
            Log.d(TAG, "Error starting camera preview: " + e.getMessage());
        }
    }
}

处理相机角度

在Android设备中，不同的设备可能有不同的相机角度，我们需要根据设备的角度来正确显示相机预览。可以通过以下步骤来处理相机角度：

flowchart TD
    A[获取设备相机信息] --> B[获取设备角度信息]
    B --> C{是否需要调整角度}
    C -- 是 --> D[调整相机角度]
    C -- 否 --> E[显示相机预览]

下面是一个示例代码，演示如何获取设备的相机角度信息并调整相机角度：

public static int getCameraDisplayOrientation(Context context, int cameraId) {
    Camera.CameraInfo info = new Camera.CameraInfo();
    Camera.getCameraInfo(cameraId, info);
    WindowManager windowManager = (WindowManager) context.getSystemService(Context.WINDOW_SERVICE);
    int rotation = windowManager.getDefaultDisplay().getRotation();
    int degrees = 0;
    switch (rotation) {
        case Surface.ROTATION_0:
            degrees = 0;
            break;
        case Surface.ROTATION_90:
            degrees = 90;
            break;
        case Surface.ROTATION_180:
            degrees = 180;
            break;
        case Surface.ROTATION_270:
            degrees = 270;
            break;
    }

    int result;
    if (info.facing == Camera.CameraInfo.CAMERA_FACING_FRONT) {
        result = (info.orientation + degrees) % 360;
        result = (360 - result) % 360;  // compensate the mirror
    } else {  // back-facing
        result = (info.orientation - degrees + 360) % 360;
    }
    return result;
}