您需要添加更多的位图在 MaskAttempt 。

public MaskAttempt(Context context) {
    super(context);
    this.setBackgroundColor(Color.WHITE);
    mPaint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.DST_IN));

    final Resources res = context.getResources();
    mItemToBeMasked = BitmapFactory.decodeResource(res, R.drawable.red_rectangle);
    mMask = BitmapFactory.decodeResource(res, R.drawable.icon_mask);
    duplicate = BitmapFactory.decodeResource(res, R.drawable.icon_mask).copy(Config.ARGB_8888, true);

    c = new Canvas(duplicate);

    x = new Paint(Paint.ANTI_ALIAS_FLAG);
    x.setColor(Color.BLACK);
    x.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.DST_IN));
}

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

    canvas.translate((getWidth() - mItemToBeMasked.getWidth()) >> 1, (getHeight() -     mItemToBeMasked.getHeight()) >> 1);

    c.drawBitmap(mItemToBeMasked, 0, 0, null);
    c.drawBitmap(mMask, 0, 0, mPaint);
    canvas.drawBitmap(duplicate, 0, 0, null);

    canvas.restore();
}