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