在Android中绘画时如何遮盖一个简单的区域？

下面是一个简化的描述：想象一下，我有一个 View 类，它可以绘制一面墙的图片，并且我想在绘制它时切出一个窗口。假设我扩展该 View 类并重写其dispatchDraw() 方法来执行以下操作。首先绘制背景（如果有的话）可以通过窗户看到。接下来我想以某种方式屏蔽矩形窗口区域，然后调用 super.dispatchDraw()。最后我想去掉面具并画一个人站在窗前，这样他们就可以画在背景和墙上。我怎样才能做到这一点？

这是一些看起来接近我需要的代码：

@Override
protected void dispatchDraw(Canvas into) {
    int w = into.getWidth();
    int h = into.getHeight();
    int w3 = w / 3;
    int h3 = h / 3;
    into.drawLine(0, 0, w, h, mPaint);
    Region protect = new Region(w / 3, h / 3, 2 * w / 3, 2 * h / 3);
    into.clipRegion(protect, Op.INTERSECT);
    into.drawColor(Color.MAGENTA); // or super.dispatchDraw() here.
}

这给了我这个：

这与我想要的有点相反。请注意上面代码中名为“protect”的区域。我希望洋红色填充无处不在except在那个地区。具体来说，我想看到的是：

以窗户为例，我应该能够消除限制并以正常方式绘制与窗户和墙壁重叠的人或物体。

编辑：这是 Rajesh CP 答案的简化工作版本。我还在最后的所有内容上添加了一个红色的“前景”条纹，以表明我可以删除限制并添加它们。谢谢拉杰什！

public class MaskTest extends Activity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(new ClippView(getApplicationContext()));
    }

    private class ClippView extends View {
        private Paint line_paint = new Paint();
        private Paint strip_paint = new Paint();

        public ClippView(Context context) {
            super(context);
            line_paint.setColor(Color.GRAY);
            line_paint.setStrokeWidth(20);
            strip_paint.setColor(Color.RED);
        }

        @Override
        protected void onDraw(Canvas canvas) {
            super.onDraw(canvas);
            int w = canvas.getWidth();
            int h = canvas.getHeight();
            int w3 = w / 3;
            int h3 = h / 3;
            // This line represents some unknown background that we are drawing over.
            canvas.drawLine(0, 0, w, h, line_paint);
            // 'protect' represents some area to not paint over until desired.
            Region protect = new Region(w3, h3, 2 * w / 3, 2 * h / 3);
            canvas.clipRegion(protect, Op.DIFFERENCE);
            // Paint magenta over the entire canvas, avoiding the protected region.
            canvas.drawColor(Color.MAGENTA);
            // Remove the protected region.
            Region all = new Region(0, 0, w, h);
            canvas.clipRegion(all, Op.UNION);
            // Draw a wide foreground strip over the entire canvas.
            canvas.drawRect(w / 2 - w / 20, 0, w / 2 + w / 20, h, strip_paint);
        }
    }
}

public class ClippView extends View{
    private Paint paint= new Paint();

    public ClippView(Context context) {
        super(context);
    }


    private Region protect;
    /*
     * (non-Javadoc)
     * @see android.view.View#onDraw(android.graphics.Canvas)
     * @since Apr 12, 2013
     * @author rajeshcp
     */
    @Override
    protected void onDraw(Canvas canvas) { 
        super.onDraw(canvas);
        // view.buildDrawingCache();      


        int w = canvas.getWidth();
        int h = canvas.getHeight();
        int w3 = w / 3;
        int h3 = h / 3;
        canvas.drawLine(0, 0, w, h, paint);
        protect = (protect == null) ? new Region(w3, h3, 2 * w / 3, 2 * h / 3) : protect;
        canvas.clipRegion(protect, Op.DIFFERENCE);
        canvas.drawColor(Color.MAGENTA);


    }

}

Do this I think this is what you want.