如何编写一个在手机上自定义水印的拍照相机

步骤：

1. 创建一个新的 Android 项目，并命名为“CustomCamera”。
2. 在项目的 build.gradle 文件中添加以下依赖项：

dependencies {
    implementation 'com.android.support:appcompat-v7:28.0.0'
    implementation 'com.android.support:design:28.0.0'
    implementation 'com.android.support:recyclerview-v7:28.0.0'
    implementation 'com.android.support:cardview-v7:28.0.0'
    implementation 'com.android.support.constraint:constraint-layout:1.1.3'
    implementation 'com.android.support:support-annotations:28.0.0'
    implementation 'com.squareup.picasso:picasso:2.5.2'
}

3. 在 AndroidManifest.xml 文件中添加以下权限：

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

4. 创建一个新的自定义相机类 CustomCameraView，继承 SurfaceView，并实现 SurfaceHolder.Callback 接口。

public class CustomCameraView extends SurfaceView implements SurfaceHolder.Callback {
    private Camera camera;
    private SurfaceHolder holder;
    
    public CustomCameraView(Context context) {
        super(context);
        holder = getHolder();
        holder.addCallback(this);
    }

    @Override
    public void surfaceCreated(SurfaceHolder holder) {
        camera = Camera.open();
        try {
            camera.setPreviewDisplay(holder);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    @Override
    public void surfaceChanged(SurfaceHolder holder, int format, int width, int height) {
        Camera.Parameters parameters = camera.getParameters();
        Camera.Size size = getBestPreviewSize(width, height, parameters);
        parameters.setPreviewSize(size.width, size.height);
        camera.setParameters(parameters);
        camera.startPreview();
    }

    @Override
    public void surfaceDestroyed(SurfaceHolder holder) {
        camera.stopPreview();
        camera.release();
    }

    private Camera.Size getBestPreviewSize(int width, int height, Camera.Parameters parameters) {
        Camera.Size result = null;
        for (Camera.Size size : parameters.getSupportedPreviewSizes()) {
            if (size.width <= width && size.height <= height) {
                if (result == null) {
                    result = size;
                } else {
                    int resultArea = result.width * result.height;
                    int newArea = size.width * size.height;
                    if (newArea > resultArea) {
                        result = size;
                    }
                }
            }
        }
        return result;
    }
}

5. 在 activity_main.xml 文件中添加以下代码：

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent">
 
    <FrameLayout
        android:id="@+id/frame_layout"
        android:layout_width="match_parent"
        android:layout_height="match_parent" />
 
    <LinearLayout
        android:id="@+id/bottom_layout"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_alignParentBottom="true"
        android:orientation="horizontal"
        android:padding="8dp">
 
        <ImageView
            android:id="@+id/image_view_watermark"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:padding="8dp"
            android:src="@drawable/ic_launcher_background" />
 
        <Button
            android:id="@+id/button_capture"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:text="Capture" />
 
        <Button
            android:id="@+id/button_gallery"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:text="Gallery" />
    </LinearLayout>
 
</RelativeLayout>

6. 在 MainActivity.java 文件中添加以下代码：

public class MainActivity extends AppCompatActivity {
    private CustomCameraView customCameraView;
    private ImageView imageViewWatermark;
    private Button buttonCapture, buttonGallery;
    private Bitmap bitmapWatermark;
 
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
 
        customCameraView = new CustomCameraView(this);
        FrameLayout frameLayout = findViewById(R.id.frame_layout);
        frameLayout.addView(customCameraView);
 
        imageViewWatermark = findViewById(R.id.image_view_watermark);
        bitmapWatermark = BitmapFactory.decodeResource(getResources(), R.drawable.watermark);
        imageViewWatermark.setImageBitmap(bitmapWatermark);
 
        buttonCapture = findViewById(R.id.button_capture);
        buttonCapture.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                customCameraView.takePicture(new Camera.PictureCallback() {
                    @Override
                    public void onPictureTaken(byte[] data, Camera camera) {
                        Bitmap bitmap = BitmapFactory.decodeByteArray(data, 0, data.length);
                        Bitmap scaledBitmap = Bitmap.createScaledBitmap(bitmap, imageViewWatermark.getWidth(), imageViewWatermark.getHeight(), false);
                        Bitmap resultBitmap = addWatermark(scaledBitmap, bitmapWatermark);
                        saveImage(resultBitmap);
                    }
                });
            }
        });
 
        buttonGallery = findViewById(R.id.button_gallery);
        buttonGallery.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Intent intent = new Intent(Intent.ACTION_PICK, MediaStore.Images.Media.EXTERNAL_CONTENT_URI);
                startActivityForResult(intent, 1);
            }
        });
    }
 
    private Bitmap addWatermark(Bitmap source, Bitmap watermark) {
        Bitmap result = Bitmap.createBitmap(source.getWidth(), source.getHeight(), source.getConfig());
        Canvas canvas = new Canvas(result);
        canvas.drawBitmap(source, 0, 0, null);
        canvas.drawBitmap(watermark, 0, 0, null);
        return result;
    }
 
    private void saveImage(Bitmap bitmap) {
        String filename = "CustomCamera_" + System.currentTimeMillis() + ".jpg";
        File file = new File(Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_PICTURES), filename);
        try {
            FileOutputStream fos = new FileOutputStream(file);
            bitmap.compress(Bitmap.CompressFormat.JPEG, 90, fos);
            fos.close();
            Toast.makeText(this, "Image saved to " + file.getAbsolutePath(), Toast.LENGTH_LONG).show();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
 
    @Override
    protected void onActivityResult(int requestCode, int resultCode, Intent data) {
        if (requestCode == 1 && resultCode == RESULT_OK && data != null) {
            Uri uri = data.getData();
            Picasso.get().load(uri).into(imageViewWatermark);
            try {
                InputStream inputStream = getContentResolver().openInputStream(uri);
                bitmapWatermark = BitmapFactory.decodeStream(inputStream);
            } catch (FileNotFoundException e) {
                e.printStackTrace();
            }
        }
        super.onActivityResult(requestCode, resultCode, data);
    }
}

7. 编译并运行应用程序，在拍照时会显示一个水印图像，可以从相册中选择一个新的水印图像。当用户点击拍照按钮时，将拍摄的照片与水印合并，并将其保存到外部存储器的图片目录中。