主要思想：
将一个view设计成多层：背景层，含中奖信息等；
遮盖层，用于刮奖，使用关联一个Bitmap的Canvas
在该Bitmap上，使用它的canvas.drawPath的api来处理 手势滑动(类似刮奖的动作)
使用paint.setXfermode 来进行消除手势滑动区域

public class GuaView extends View { private Bitmap mBitmap; //遮盖的图层 private Canvas mCanvas; //绘制遮盖图层 private Paint mOuterPaint; private Path mPath; private float mLastX; private float mLastY; private Bitmap mCoverBitmap; //遮盖图 private int mWidth, mHeight; private Paint mInnerPaint; private String mInfo; public GuaView(Context context) { this(context, null); } public GuaView(Context context, AttributeSet attrs) { super(context, attrs); init(); } private void init() { mPath = new Path(); mOuterPaint = new Paint(); mInnerPaint = new Paint(); mCoverBitmap = BitmapFactory.decodeResource(getResources(), R.drawable.fg_guaguaka); mInfo = "￥ 5 0 0"; } @Override protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) { super.onMeasure(widthMeasureSpec, heightMeasureSpec); mWidth = mCoverBitmap.getWidth(); mHeight = mCoverBitmap.getHeight(); setMeasuredDimension(mWidth, mHeight); mBitmap = Bitmap.createBitmap(mWidth, mHeight, Bitmap.Config.ARGB_8888); mCanvas = new Canvas(mBitmap); mCanvas.drawBitmap(mCoverBitmap, 0, 0, null); setOuterPaint(); setInnerPaint(); } private void setInnerPaint() { mInnerPaint.setColor(Color.RED); mInnerPaint.setStyle(Paint.Style.STROKE); mInnerPaint.setStrokeCap(Paint.Cap.ROUND); mInnerPaint.setStrokeJoin(Paint.Join.ROUND); mInnerPaint.setAntiAlias(true); mInnerPaint.setDither(true); //防抖 mInnerPaint.setStrokeWidth(5); mInnerPaint.setTextSize(100); mInnerPaint.setTextAlign(Paint.Align.CENTER); } private void setOuterPaint() { mOuterPaint.setColor(Color.GREEN); mOuterPaint.setStyle(Paint.Style.STROKE); mOuterPaint.setStrokeCap(Paint.Cap.ROUND); mOuterPaint.setStrokeJoin(Paint.Join.ROUND); mOuterPaint.setAntiAlias(true); mOuterPaint.setDither(true); //防抖 mOuterPaint.setStrokeWidth(20); } @Override //Path public boolean onTouchEvent(MotionEvent event) { float x = event.getX(); float y = event.getY(); switch (event.getAction()) { case MotionEvent.ACTION_DOWN: mLastX = x; mLastY = y; mPath.moveTo(x, y); break; case MotionEvent.ACTION_MOVE: float deltaX = Math.abs(x - mLastX); float deltaY = Math.abs(y - mLastY); if (deltaX > 5 || deltaY > 5) { mPath.lineTo(x, y); } mLastX = x; mLastY = y; break; case MotionEvent.ACTION_UP: break; } invalidate();//调用onDraw return true; } @Override protected void onDraw(Canvas canvas) { super.onDraw(canvas); canvas.drawColor(Color.parseColor("#bbbbbb")); //背景底色 灰色 canvas.drawText(mInfo, mWidth / 2, mHeight / 4 * 3, mInnerPaint); //绘制文本 canvas.drawBitmap(mBitmap, 0, 0, null); //绘制mBitmap 这是一个可变的bitmap，通过mCanvas绘制，首先绘制了mCoverBitmap drawPath(); } private void drawPath() { //使用该mode：dst和src相交后， 只保留dst，且除去相交的部份 mOuterPaint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.DST_OUT)); mCanvas.drawPath(mPath, mOuterPaint); } }

Paint.Join 连续画笔衔接时：

• MITER 在外边缘以一个锐角连接
• ROUND 以圆弧
• BEVEL 以直线

Paint.Cap 指定对于 线和路径(lines and paths) 的开始和结束点的处理方式：

• BUTT ends with the path 不超越它
• ROUND with the center at the end of the path 半圆
• SQUARE with the center at the end of the path 方形