Android刮刮卡效果实现代码

/** 
 * Created by 57 on 2016-4-21. 
 */ 
public class XfermodeView extends View{ 
 private Bitmap mBgBitmap,mFgBitmap; 
 private Paint mPaint; 
 private Canvas mCanvas; 
 private Path mPath; 
 
 public XfermodeView(Context context) { 
 super(context); 
 init(); 
 } 
 
 
 public XfermodeView(Context context, AttributeSet attrs) { 
 super(context, attrs); 
 init(); 
 } 
 
 public XfermodeView(Context context, AttributeSet attrs, int defStyleAttr) { 
 super(context, attrs, defStyleAttr); 
 init(); 
 } 
 
 @Override 
 protected void onDraw(Canvas canvas) { 
 
 canvas.drawBitmap(mBgBitmap,0,0,null); 
 canvas.drawBitmap(mFgBitmap,0,0,null); 
 } 
 
 
 private void init() { 
 mPaint = new Paint(); 
 mPaint.setAlpha(0); 
 mPaint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.DST_IN)); 
 mPaint.setStyle(Paint.Style.STROKE); 
 mPaint.setStrokeJoin(Paint.Join.ROUND); 
 mPaint.setStrokeWidth(50); 
 mPaint.setStrokeCap(Paint.Cap.ROUND); 
 mPath = new Path(); 
 mBgBitmap = BitmapFactory.decodeResource(getResources(), R.drawable.test5); 
 mFgBitmap = Bitmap.createBitmap(mBgBitmap.getWidth(),mBgBitmap.getHeight(),Bitmap.Config.ARGB_8888); 
 mCanvas = new Canvas(mFgBitmap); 
 mCanvas.drawColor(Color.GRAY); 
 
 } 
 
 @Override 
 public boolean onTouchEvent(MotionEvent event) { 
 switch(event.getAction()){ 
  case MotionEvent.ACTION_DOWN: 
  mPath.reset(); 
  mPath.moveTo(event.getX(),event.getY()); 
  break; 
  case MotionEvent.ACTION_MOVE: 
  mPath.lineTo(event.getX(),event.getY()); 
  break; 
 } 
 mCanvas.drawPath(mPath,mPaint); 
 invalidate(); 
 return true; 
 } 
}