Android刮刮卡效果

                    

不多说，直接上代码：

 package com.example.test;

 import android.app.Activity;
 import android.content.Context;
 import android.graphics.Bitmap;
 import android.graphics.Bitmap.Config;
 import android.graphics.Canvas;
 import android.graphics.Color;
 import android.graphics.Paint;
 import android.graphics.Paint.Cap;
 import android.graphics.Paint.Join;
 import android.graphics.Paint.Style;
 import android.graphics.Path;
 import android.graphics.PorterDuff.Mode;
 import android.graphics.PorterDuffXfermode;
 import android.graphics.drawable.BitmapDrawable;
 import android.os.Bundle;
 import android.util.DisplayMetrics;
 import android.view.MotionEvent;
 import android.view.View;

 public class GuaGuaKaActivity extends Activity {
     int screenWidth = 0;
     int screenHeight = 0;
     @Override
     protected void onCreate(Bundle savedInstanceState) {
         super.onCreate(savedInstanceState);

         DisplayMetrics dm  = new DisplayMetrics();
         getWindowManager().getDefaultDisplay().getMetrics(dm);
         screenWidth = dm.widthPixels;
         screenHeight = dm.heightPixels;

         setContentView(new GuaGuaKa(this));
     }
     class GuaGuaKa extends View{
         private Canvas mCanvas = null;
         private Path mPath = null;
         private Paint mPaint = null;
         private Bitmap bitmap = null;
         public GuaGuaKa(Context context) {
             super(context);
             init(context);
         }

         private void init(Context context) {
             setBackground();

             mPath = new Path();
             bitmap = Bitmap.createBitmap(screenWidth, screenHeight, Config.ARGB_8888);
             mPaint = new Paint();
             mPaint.setFlags(Paint.ANTI_ALIAS_FLAG);
             mPaint.setAntiAlias(true);
             mPaint.setDither(true);
             mPaint.setStyle(Style.STROKE);
             mPaint.setStrokeWidth(10);
             mPaint.setStrokeCap(Cap.ROUND);
             mPaint.setStrokeJoin(Join.ROUND);
             mPaint.setXfermode(new PorterDuffXfermode(Mode.DST_IN));
             mPaint.setAlpha(0);

             mCanvas = new Canvas(bitmap);
             mCanvas.drawColor(Color.GRAY);
         }

         private void setBackground() {
             Paint paint = new Paint();
             Bitmap bitmap = Bitmap.createBitmap(screenWidth,screenHeight,Config.ARGB_8888);
             paint.setTextSize(30);
             paint.setColor(Color.BLACK);
             paint.setFlags(Paint.ANTI_ALIAS_FLAG);
             paint.setAntiAlias(true);

             Canvas canvas = new Canvas(bitmap);
             canvas.drawColor(Color.WHITE);
             canvas.drawText("谢谢惠顾", 100, 100, paint);
             canvas.drawText("再来10瓶", 100, 250, paint);
             setBackgroundDrawable(new BitmapDrawable(getResources(), bitmap));

         }

         @Override
         protected void onDraw(Canvas canvas) {
             super.onDraw(canvas);
             mCanvas.drawPath(mPath, mPaint);
             canvas.drawBitmap(bitmap, 0, 0, null);
         }
         int x = 0;
         int y = 0;
         @Override
         public boolean onTouchEvent(MotionEvent event) {
             int action = event.getAction();
             int currX = (int) event.getX();
             int currY = (int) event.getY();
             switch(action){
                 case MotionEvent.ACTION_DOWN:{
                     mPath.reset();
                     x = currX;
                     y = currY;
                     mPath.moveTo(x, y);
                 }break;
                 case MotionEvent.ACTION_MOVE:{
                     mPath.quadTo(x, y, currX, currY);
                     x = currX;
                     y = currY;
                     postInvalidate();
                 }break;
                 case MotionEvent.ACTION_UP:
                 case MotionEvent.ACTION_CANCEL:{
                     mPath.reset();
                 }break;
             }
             return true;
         }
     }
 }

参考：

1、Android中Path类的lineTo方法和quadTo方法画线的区别：http://blog.csdn.net/stevenhu_223/article/details/9229337

2、android.graphics.Paint方法setXfermode ：http://my.oschina.net/smalant/blog/40328