思想：

將一個View設計成多層，內層（包括中獎信息）和外層（用于刮獎），外層的圖層用Canvas與一個Bitmap關聯(lián)，用這個關聯(lián)的Bitmap來處理手勢的滑動，類似于刮獎的動作。

使用paint.setXfermode 來進行消除手勢滑動區(qū)域

import android.content.Context;  
import android.graphics.Bitmap;  
import android.graphics.BitmapFactory;  
import android.graphics.Canvas;  
import android.graphics.Color;  
import android.graphics.Paint;  
import android.graphics.Path;  
import android.graphics.PorterDuff;  
import android.graphics.PorterDuffXfermode;  
import android.util.AttributeSet;  
import android.view.MotionEvent;  
import android.view.View;  
  
/** 
 * Created by Administrator on 2015/7/29. 
 */  
public class GuaView extends View {  
    private Path mPath;  
    private Paint mInnerPaint;  //內層圖層Paint  
    private Paint mOuterPaint;  //外層圖層Paint  
    private Bitmap mGuaBitmap;  //用于處理刮獎的Bitmap  
    private Bitmap mOuterBitmap;  //外層圖層Bitmap  
    private Canvas mCanvas;  
  
    private int mWidth, mHeight;  
  
    private float mLastX;  
    private float mLastY;  
  
    private String mText;  
  
    public GuaView(Context context, AttributeSet attrs) {  
        super(context, attrs);  
        init();  
    }  
  
    private void init() {  
        mPath = new Path();  
        mOuterPaint = new Paint();  
        mInnerPaint = new Paint();  
  
        //創(chuàng)建外層圖層  
        mOuterBitmap = BitmapFactory.decodeResource(getResources(), R.drawable.guaguaka).copy(Bitmap.Config.ARGB_8888, true);  
        mText = "¥500";  
    }  
  
    @Override  
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {  
        super.onMeasure(widthMeasureSpec, heightMeasureSpec);  
  
        mWidth = mOuterBitmap.getWidth();  
        mHeight = mOuterBitmap.getHeight();  
  
        //創(chuàng)建內層圖層  
        mGuaBitmap = Bitmap.createBitmap(mWidth, mHeight, Bitmap.Config.ARGB_8888);  
        mCanvas = new Canvas(mGuaBitmap);  
        mCanvas.drawBitmap(mOuterBitmap, 0, 0, null); //將mOuterBitmap畫到mCanvas上，與mGuaBitmap關聯(lián)  
  
        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();  
        return true;  
    }  
  
    @Override  
    protected void onDraw(Canvas canvas) {  
        super.onDraw(canvas);  
  
        canvas.drawColor(Color.parseColor("#bbbbbb")); //背景底色  灰色  
        canvas.drawText(mText, mWidth / 2, mHeight / 4 * 3, mInnerPaint); //繪制文本  
        canvas.drawBitmap(mGuaBitmap, 0, 0, null); //繪制外層Bitmap, 將mBitmap顯示在界面上  
        drawPath();  
    }  
  
    private void drawPath() {  
        //使用該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);  
    }  
}  

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