Android刮刮卡特效

package com.example.xfermodeview;

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;

public class XfermodeView   extends View{




	private Bitmap mBgBitmap;  //定义背景
	private Bitmap mFgBitmap;	//定义上层图片
	private Paint mPaint;		//定义画笔
	private Canvas mCanvas;	 //定义画布
	private Path  mPath;	//定义手指移动轨迹
	
	public XfermodeView(Context context, AttributeSet attrs) {
		super(context, attrs);
		init();
	}

	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);  //让笔触和连接处更原滑
		mPaint.setStrokeWidth(50);
		mPaint.setStrokeCap(Paint.Cap.ROUND);
		mPath=new Path();
		mBgBitmap=BitmapFactory.decodeResource(getResources(),R.drawable.qq);
		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;
	}
	

	@Override
	protected void onDraw(Canvas canvas) {
		canvas.drawBitmap(mBgBitmap, 0,0, null);
		canvas.drawBitmap(mFgBitmap, 0,0, null);
	}
}