private void drawPath() { mFingerPaint.setStyle(Paint.Style.STROKE); // 设置两张图片相交时的模式(取下层绘制非交集部分) mFingerPaint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.DST_OUT)); mCanvas.drawPath(mPath, mFingerPaint); }
测量和绘制过程如下：

@Override protected void onDraw(Canvas canvas) { canvas.drawText(mText, getWidth() / 2 - mTextBound.width() / 2, getHeight() / 2 + mTextBound.height() / 2, mBackPint); if (!isComplete) { drawPath(); canvas.drawBitmap(mBitmap, 0, 0, null); } } @Override protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) { super.onMeasure(widthMeasureSpec, heightMeasureSpec); int width = getMeasuredWidth(); int height = getMeasuredHeight(); // 初始化bitmap mBitmap = Bitmap.createBitmap(width, height, Config.ARGB_8888); mCanvas = new Canvas(mBitmap); // 绘制遮盖层 mFingerPaint.setStyle(Paint.Style.FILL); mCanvas.drawRoundRect(new RectF(0, 0, width, height), 30, 30, mFingerPaint); mCanvas.drawBitmap(BitmapFactory.decodeResource(getResources(), R.drawable.mask), null, new RectF(0, 0, width, height), null); }
此外还有一篇也是使用了此技术的博客，点击这里进行查看。