线性布局画布绘制突然滞后

Question

在使用Canvas绘制线性布局内部时，我只需要您一些有关滞后问题的帮助。当版面没有背景时，该应用看起来非常流畅。但是当我放一些的时候。它突然停滞了。

这里是代码

public class PaintFinderDemo extends AppCompatActivity {

DrawingView dv ;
LinearLayout layout;
private Paint mPaint;

ColoringActivity.MyView mv;
Drawable d;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    dv = new DrawingView(this);
    setContentView(R.layout.coloring_mode_activity);
    layout = findViewById(R.id.image_draw);
    layout.addView(dv);

    mPaint = new Paint();
    mPaint.setAntiAlias(true);
    mPaint.setDither(true);
    mPaint.setColor(Color.GREEN);
    mPaint.setStyle(Paint.Style.STROKE);
    mPaint.setStrokeJoin(Paint.Join.ROUND);
    mPaint.setStrokeCap(Paint.Cap.ROUND);
    mPaint.setStrokeWidth(12);
}

public class DrawingView extends View {

    public int width;
    public  int height;
    private Bitmap mBitmap;
    private Canvas mCanvas;
    private Path mPath;
    private Paint   mBitmapPaint;
    Context context;
    private Paint circlePaint;
    private Path circlePath;

    public DrawingView(Context c) {
        super(c);
        context=c;
        mPath = new Path();
        mBitmapPaint = new Paint(Paint.DITHER_FLAG);
        circlePaint = new Paint();
        circlePath = new Path();
        circlePaint.setAntiAlias(true);
        circlePaint.setColor(Color.BLUE);
        circlePaint.setStyle(Paint.Style.STROKE);
        circlePaint.setStrokeJoin(Paint.Join.MITER);
        circlePaint.setStrokeWidth(4f);
    }

    @Override
    protected void onSizeChanged(int w, int h, int oldw, int oldh) {
        super.onSizeChanged(w, h, oldw, oldh);

        mBitmap = Bitmap.createBitmap(w, h, Bitmap.Config.ARGB_8888);
        mCanvas = new Canvas(mBitmap);
    }

    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        Drawable d = getResources().getDrawable(R.drawable.bird);
        d.setBounds(50, 50, 50, 50);
        d.draw(canvas);
        canvas.drawBitmap( mBitmap, 0, 0, mBitmapPaint);
        canvas.drawPath( mPath,  mPaint);
        canvas.drawPath( circlePath,  circlePaint);
    }

    private float mX, mY;
    private static final float TOUCH_TOLERANCE = 4;

    private void touch_start(float x, float y) {
        mPath.reset();
        mPath.moveTo(x, y);
        mX = x;
        mY = y;
    }

    private void touch_move(float x, float y) {
        float dx = Math.abs(x - mX);
        float dy = Math.abs(y - mY);
        if (dx >= TOUCH_TOLERANCE || dy >= TOUCH_TOLERANCE) {
            mPath.quadTo(mX, mY, (x + mX)/2, (y + mY)/2);
            mX = x;
            mY = y;

            circlePath.reset();
            circlePath.addCircle(mX, mY, 30, Path.Direction.CW);
        }
    }

    private void touch_up() {
        mPath.lineTo(mX, mY);
        circlePath.reset();
        // commit the path to our offscreen
        mCanvas.drawPath(mPath,  mPaint);
        // kill this so we don't double draw
        mPath.reset();
    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        float x = event.getX();
        float y = event.getY();

        switch (event.getAction()) {
            case MotionEvent.ACTION_DOWN:
                touch_start(x, y);
                invalidate();
                break;
            case MotionEvent.ACTION_MOVE:
                touch_move(x, y);
                invalidate();
                break;
            case MotionEvent.ACTION_UP:
                touch_up();
                invalidate();
                break;
        }
        return true;
    }
}

我当前绘制的线性布局：

<LinearLayout
    android:id="@+id/image_draw"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:layout_below="@+id/header"
    android:layout_above="@id/color_picker"
    android:background="@drawable/bird" // It doesn't lag when I remove this code
    android:layout_margin="40dp">

</LinearLayout>

确实需要您的一些帮助。我真的无法在互联网上找到解决此类问题的方法。