CanvasでBitmap画像に図形を重ねて描画

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/activity_main"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:padding="0dip"
    tools:context="com.nullproduct.blogsample.MainActivity">

    <com.nullproduct.blogsample.CanvasView
        android:id="@+id/CanvasView"
        android:layout_height="match_parent"
        android:layout_width="match_parent" />
</RelativeLayout>

CanvasView.java

public class CanvasView extends View {
    private Bitmap mBitmap;
    List<List<Point>> mPoints;

    public CanvasView(Context context, AttributeSet attrs) {
        super(context, attrs);

        mBitmap = null;
        mPoints = null;
    }

    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);

        canvasDraw(canvas);
    }

    private void canvasDraw(Canvas canvas) {
        Paint paint = new Paint();
        paint.setStrokeWidth(100);

        /* ⑤：背景色を設定 */
        canvas.drawColor(Color.BLACK);

        /* ⑥：原画像（Bitmap）を描画 */
        if(mBitmap != null) {
            float scale = (float)getWidth() / mBitmap.getWidth();
            canvas.scale(scale, scale);
            canvas.drawBitmap(mBitmap, 0, 0, paint);
        }

        /* ⑦：輪郭を描画 */
        if(mPoints != null) {
            Path path = new Path();
            paint.setAntiAlias(true);
            paint.setStyle(Paint.Style.STROKE);
            paint.setColor(Color.argb(128, 255, 0, 0));

            for(int i = 0; i < mPoints.size(); i++) {
                List<Point> point = mPoints.get(i);

                path.moveTo((float)point.get(0).x, (float)point.get(0).y);
                for(int j = 0; j < point.size(); j++) {
                    path.lineTo((float)point.get(j).x, (float)point.get(j).y);
                }
                path.lineTo((float)point.get(0).x, (float)point.get(0).y);
                for(int j = 0; j < point.size(); j++) {
                    path.lineTo((float)point.get(j).x, (float)point.get(j).y);
                }
            }

            canvas.drawPath(path, paint);
        }
    }

    public void setmBitmap(Bitmap bmp) {
        mBitmap = bmp;
    }

    public void setmPoints(List<List<Point>> points) {
        mPoints = points;
    }
}

MainActivity.java

public class MainActivity extends AppCompatActivity {

    static {
        System.loadLibrary("opencv_java3");
    }

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

        onImageScan();
    }

    private void onImageScan() {
        /* 画像読み込み */
        Bitmap bmp = BitmapFactory.decodeResource(getResources(), R.drawable.src);
        Mat mat = new Mat();
        Utils.bitmapToMat(bmp, mat, true);

        /* 画像を二値化 */
        mat = getThreshold(mat);

        /* 輪郭の座標を取得 */
        List<MatOfPoint> contours = getContour(mat);
        List<List<Point>> points = contour2point(contours);

        /* ①：描画先のVIEWを取得 */
        CanvasView canvasView =  (CanvasView)findViewById(R.id.CanvasView);
        /* ②：VIEWに原画像（Bitmap）を登録 */
        canvasView.setmBitmap(bmp);
        /* ③：VIEWに抽出した輪郭座標を登録 */
        canvasView.setmPoints(points);
        /* ④：VIEWの描画更新要求 */
        canvasView.invalidate();
    }
}