安卓开发（二）人脸识别相册FaceMap

本篇主要讲本科时做的一个应用，人脸识别相册。主要包含JNI和业务逻辑。最终代码会公布在github。

算法部分

当时深度学习还没有很火，所以用的是经典的PCA方法，降维之后直接作为特征。人脸检测部分用的也是Opencv的Haar特征人脸检测。现在来看性能比较差了。这里就不介绍算法了，感兴趣的可以看看我的其他博文。

系统架构">系统架构

本次系统架构分成2部分，一是算法；二是界面和业务逻辑。算法部分由于是C++写的，所以需要用Java的JNI接口封装一下。界面方面采用瀑布流界面，三栏极简风格。
业务逻辑是：
1.用户打开相册，自动读取系统照片；
2.用户点击某一张图像，若此照片此前未检测，则检测人脸并提取特征；若此照片此前已经检测，则显示人脸位置。
3.用户点击人脸，手工标注。
4.在第三栏，按照人脸识别实现自动分类。
这个逻辑的缺点是一开始需要用户手动标记，现在看来大概可以用聚类算法代替。

算法的JNI封装

因为我已经不做开发了，所以现在并不知道JNI怎么写了，已经不会写了。还是贴贴代码吧：

package cn.edu.zju.srtp.facemap.algorithm;

import java.io.File;
import java.util.Vector;

import org.opencv.core.Mat;

import android.content.Context;
import android.util.Log;

public class NativeFaceRecognizer {
    public static final int          LBPH_FACERECOGNIZER   =1;
    public static final int          FISHER_FACERECOGNIZER =2;
    public static final int          EIGEN_FACERECOGNIZER  =3;
    private final static String      TAG                   ="NativeFaceRecognizer";

    public final static String       LBPH_FILENAME         ="lbph_model.xml";
    public final static String       FISHER_FILENAME       ="fisher_model.xml";
    public final static String       EIGEN_FILENAME        ="eigen_model.xml";

    /**Note which faceRecognizer has been created
     * 
     */
    private int                      mState                =1;

    /**The pointer to faceRecognizer with the initial value -1(important)
     * 
     */
    private long                     mNativeObj            =-1;

    private Context                  mContext;

    static{
        Log.d(TAG, "NativeFaceRecognizer static initial block enter");
        System.loadLibrary("opencv_java");
        System.loadLibrary("face_rec");
        Log.d(TAG, "NativeFaceRecognizer static initial block exit");

    }

    public NativeFaceRecognizer(Context context,int state) {
        mContext=context;
        mState=state;
        createFaceRecognizer();
        load();
    }
    /**Destroy the model first and create a FisherFaceRecognizer model.
     *   
     */
    public void createFisherFaceRecognizer(){
        destroy();
        mState=FISHER_FACERECOGNIZER;
        mNativeObj=nativeCreateFisherFaceRecognizer();
    }

    /**Destroy the model first and create a LBPHFaceRecognizer model.
     *   
     */
    public void createLBPHFaceRecognizer(){
        destroy();
        mState=LBPH_FACERECOGNIZER;
        mNativeObj=nativeCreateLBPHFaceRecognizer();
    }

    /**Destroy the model first and create a EigenFaceRecognizer model.
     *   
     */
    public void createEigenFaceRecognizer(){
        destroy();
        mState=EIGEN_FACERECOGNIZER;
        mNativeObj=nativeCreateEigenFaceRecognizer();
    }


    /**Train the model.The input image should be grayscale.
     * The number of input images and labels should be equal.
     * @param images
     * @param labels_vec
     */
    public void train(Vectorimages,Vectorlabels_vec){
        if(mNativeObj==-1){
            Log.d(TAG,"Error:No faceRecognizer for training");
            return;
        }
        if(images.size()!=labels_vec.size()){
            Log.d(TAG, "The number of input images and labels are not eaual!");
            return;
        }
        //get the array of Mat address
        long imagesAddr[]=new long[images.size()];
        int i=0;
        int[]labels=new int[labels_vec.size()];
        for(Mat image:images){
            if(image.width()!=image.height()||image.channels()!=1||image.width()<=0){
                Log.d(TAG, "The intput images for training is illegal!" +
                        "image.width="+image.width()+" image.height="+image.height()
                        +"image.channels="+image.channels());
                return;

            }
            imagesAddr[i]=image.getNativeObjAddr();
            labels[i]=labels_vec.elementAt(i).intValue();
            i++;
        }
        nativeTrain(mNativeObj,imagesAddr,labels);
    }

    public int predict(Mat image){
        if(mNativeObj==-1){
            Log.d(TAG,"Error:No faceRecognizer for predict.");
            return -1;
        }

        return nativePredict(mNativeObj,image.getNativeObjAddr());
    }

    /**Only LBPHfaceRecognizer can be updated.
     * 
     * @param images
     * @param labels_vec
     */

    public void update(Vectorimages,Vectorlabels_vec){
        if(mState!=LBPH_FACERECOGNIZER){
            Log.d(TAG,"Error:This kind of model"+" cannot be updated.");
            return;
        }
        if(mNativeObj==-1){
            Log.d(TAG,"Error:No faceRecognizer for model update.");
            createLBPHFaceRecognizer();
        }
        //get the array of Mat address
        long imagesAddr[]=new long[images.size()];
        int i=0;
        int[]labels=new int[labels_vec.size()];
        for(Mat image:images){
            if(image.width()!=image.height()||image.channels()!=1||image.width()<=0){
                Log.d(TAG, "The intput images for training is illegal!" +
                        "image.width="+image.width()+" image.height="+image.height()
                        +"image.channels="+image.channels());
                return;

            }
            imagesAddr[i]=image.getNativeObjAddr();
            labels[i]=labels_vec.elementAt(i).intValue();
            i++;
        }
        nativeUpdate(mNativeObj, imagesAddr, labels);
        return;
    }

    /**Save the model to file.
     * 
     */
    public void save(){
        if(mNativeObj==-1){
            Log.d(TAG,"Error:No faceRecognizer to save");
            return;
        }
        String path=mContext.getFilesDir()+"/"+getFileName();
        nativeSave(mNativeObj, path);
    }

    public void load(){
        if(mNativeObj==-1){
            Log.d(TAG,"Error:No faceRecognizer to load");
            return;
        }

        String path=mContext.getFilesDir()+"/"+getFileName();
        File f=new File(path);
        if(f.exists()){
            try{
                nativeLoad(mNativeObj, path);
            }catch(Exception e){
                Log.d(TAG,"load file Alert:model doesn't exists.");
            }
        }

    }

    public void destroy(){
        if(mNativeObj!=-1){
            nativeDestroyObject(mNativeObj);
            mNativeObj=-1;
        }
        else{
            Log.d(TAG,"Cannot delete an illegal pointer");
        }
    }

    /**
     *Clear the model file. 
     */
    public Boolean clear(){
        String fileName=getFileName();
        File f=new File(mContext.getFilesDir()+"/"+fileName);
        if(f.exists()){
            return mContext.deleteFile(fileName);           
        }
        return false;
    }

    private String getFileName(){
        String fileName=new String();
        if(mState==LBPH_FACERECOGNIZER){
            fileName=LBPH_FILENAME;
        }else if(mState==FISHER_FACERECOGNIZER){
            fileName=FISHER_FILENAME;
        }else if(mState==EIGEN_FACERECOGNIZER){
            fileName=EIGEN_FILENAME;
        }else{
            return null;
        }
        return fileName;
    }

    private void createFaceRecognizer(){
        if(mState==LBPH_FACERECOGNIZER){
            createLBPHFaceRecognizer();         
        }else if(mState==FISHER_FACERECOGNIZER){
            createFisherFaceRecognizer();
        }else if(mState==EIGEN_FACERECOGNIZER){
            createEigenFaceRecognizer();
        }
    }

    public int getState(){
        return mState;
    }


    private static native long nativeCreateFisherFaceRecognizer();
    private static native long nativeCreateLBPHFaceRecognizer();
    private static native long nativeCreateEigenFaceRecognizer();

    private static native void nativeTrain(long thiz,long[]images,int[]labels);
    private static native void nativeUpdate(long thiz,long[]images,int[]labels);
    private static native int nativePredict(long thiz,long image);
    private static native void nativeSave(long thiz,String fileName);
    private static native void nativeLoad(long thiz,String fileName);
    private static native void nativeDestroyObject(long thiz);

}

依稀记得当时写这个碰到了一些问题。主要的问题是，我在C++里写的类，需要动态分配，然后把它的指针保存在Java里。每次Java把这个指针再传给C++。这种方式是以Java为主的编程方式。不知道还有没有其他更好的写法。

图像缩放

当时为了实现图像缩放，在图书馆写了一上午。主要觉得挺好玩的。年少。

package cn.edu.zju.srtp.facemap.album;

import java.util.ArrayList;
import java.util.Calendar;

import org.opencv.core.Rect;

import android.app.AlertDialog;
import android.content.Context;
import android.content.DialogInterface;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Matrix;
import android.graphics.Paint;
import android.text.format.Time;
import android.util.AttributeSet;
import android.util.Log;
import android.view.MotionEvent;
import android.view.View;
import android.widget.EditText;
import android.widget.Toast;
import cn.edu.zju.srtp.facemap.R;
import cn.edu.zju.srtp.facemap.algorithm.Face;
import cn.edu.zju.srtp.facemap.algorithm.FaceRecManagerSingleInstance;

public class ZoomImageView extends View{
    private static final String         TAG     ="ZoomImageView";
    /** 
     * 初始化状态常量 
     */  
    public static final int STATUS_INIT = 1;  

    /** 
     * 图片放大状态常量 
     */  
    public static final int STATUS_ZOOM_OUT = 2;  

    /** 
     * 图片缩小状态常量 
     */  
    public static final int STATUS_ZOOM_IN = 3;  

    /** 
     * 图片拖动状态常量 
     */  
    public static final int STATUS_MOVE = 4;  

    /** 
     * 用于对图片进行移动和缩放变换的矩阵 
     */  
    private Matrix matrix = new Matrix();  

    /** 
     * 待展示的Bitmap对象 
     */  
    private Bitmap sourceBitmap;
    /**
     *图片边框 
     */
    private Bitmap borderBitmap;
    /** 
     * 记录当前操作的状态，可选值为STATUS_INIT、STATUS_ZOOM_OUT、STATUS_ZOOM_IN和STATUS_MOVE 
     */  
    private int currentStatus;  

    private ArrayList mFaces=new ArrayList();

    private int             mInSampleSize           =1;

    private Paint           mPaint=new Paint();

    private Bitmap          mBackground;

    private Time            mTime   =new Time();

    private long            mStartTime;

    private Face            mFaceClicked;

    /** 
     * ZoomImageView控件的宽度 
     */  
    private int width;  

    /** 
     * ZoomImageView控件的高度 
     */  
    private int height;  
    /** 
     * 记录两指同时放在屏幕上时，中心点的横坐标值 
     */  
    private float centerPointX;  
    /** 
     * 记录两指同时放在屏幕上时，中心点的纵坐标值 
     */  
    private float centerPointY;  
    /** 
     * 记录当前图片的宽度，图片被缩放时，这个值会一起变动 
     */  
    private float currentBitmapWidth;  
    /** 
     * 记录当前图片的高度，图片被缩放时，这个值会一起变动 
     */  
    private float currentBitmapHeight;  
    /** 
     * 记录上次手指移动时的横坐标 
     */  
    private float lastXMove = -1;  

    /** 
     * 记录上次手指移动时的纵坐标 
     */  
    private float lastYMove = -1;  

    /** 
     * 记录手指在横坐标方向上的移动距离 
     */  
    private float movedDistanceX;  

    /** 
     * 记录手指在纵坐标方向上的移动距离 
     */  
    private float movedDistanceY;  
    /** 
     * 记录图片在矩阵上的横向偏移值 
     */  
    private float totalTranslateX;  

    /** 
     * 记录图片在矩阵上的纵向偏移值 
     */  
    private float totalTranslateY;  

    /** 
     * 记录图片在矩阵上的总缩放比例 
     */  
    private float totalRatio;  
    /** 
     * 记录手指移动的距离所造成的缩放比例 
     */  
    private float scaledRatio;  

    /** 
     * 记录图片初始化时的缩放比例 
     */  
    private float initRatio;  

    /** 
     * 记录上次两指之间的距离 
     */  
    private double lastFingerDis;  


    /** 
     * ZoomImageView构造函数，将当前操作状态设为STATUS_INIT。 
     *  
     * @param context 
     * @param attrs 
     */  
    public ZoomImageView(Context context, AttributeSet attrs) {  
        super(context, attrs);  
        currentStatus = STATUS_INIT;  
        mPaint.setColor(Color.WHITE);
        mPaint.setStrokeWidth(2);
        mPaint.setStyle(Paint.Style.STROKE);
        borderBitmap=BitmapFactory.decodeResource(getResources(), R.drawable.picture_frame_default);
    }  

    /** 
     * 将待展示的图片设置进来。 
     *  
     * @param bitmap 
     *            待展示的Bitmap对象 
     */  
    public void setImageBitmap(Bitmap bitmap) {  
        sourceBitmap = bitmap;  
        invalidate();  
    }  

    public void setInSampleSize(int inSampleSize){
        mInSampleSize=inSampleSize;
    }

    public void setFaces(ArrayListfaces){
        mFaces=(ArrayList) faces.clone();
        invalidate();
    }

    @Override  
    protected void onLayout(boolean changed, int left, int top, int right, int bottom) {  
        super.onLayout(changed, left, top, right, bottom);  
        if (changed) {  
            // 分别获取到ZoomImageView的宽度和高度  
            width = getWidth();  
            height = getHeight();  
        }  
    }  



    @Override  
    public boolean onTouchEvent(MotionEvent event) {  
        if(totalRatio>initRatio){           
            getParent().requestDisallowInterceptTouchEvent(true);
        }else{
            getParent().requestDisallowInterceptTouchEvent(false);          
        }
        switch (event.getActionMasked()) {  
        case MotionEvent.ACTION_POINTER_DOWN:  
             if (event.getPointerCount() == 2) {  
                 // 当有两个手指按在屏幕上时，计算两指之间的距离  
                 lastFingerDis = distanceBetweenFingers(event);  
             }
             break;  
        case MotionEvent.ACTION_DOWN:
//          mTime.setToNow();
            mStartTime=Calendar.getInstance().getTimeInMillis();
        case MotionEvent.ACTION_MOVE:  
            if (event.getPointerCount() == 1) {  
                // 只有单指按在屏幕上移动时，为拖动状态  
                float xMove = event.getX();  
                float yMove = event.getY();  
                if (lastXMove == -1 && lastYMove == -1) {  
                    lastXMove = xMove;  
                    lastYMove = yMove;  
                }  
                currentStatus = STATUS_MOVE;
                movedDistanceX = xMove - lastXMove;  
                movedDistanceY = yMove - lastYMove;  
                // 进行边界检查，不允许将图片拖出边界  
                if (totalTranslateX + movedDistanceX > 0) {  
                    movedDistanceX = 0;  
                } else if (width - (totalTranslateX + movedDistanceX) > currentBitmapWidth) {  
                    movedDistanceX = 0;  
                }  
                if (totalTranslateY + movedDistanceY > 0) {  
                    movedDistanceY = 0;  
                } else if (height - (totalTranslateY + movedDistanceY) > currentBitmapHeight) {  
                    movedDistanceY = 0;  
                }  
                // 调用onDraw()方法绘制图片  
                invalidate();  
                lastXMove = xMove;  
                lastYMove = yMove;  
            }else if(event.getPointerCount() == 2){
                // 有两个手指按在屏幕上移动时，为缩放状态  
                centerPointBetweenFingers(event);  
                double fingerDis = distanceBetweenFingers(event);  
                if (fingerDis > lastFingerDis) {  
                    currentStatus = STATUS_ZOOM_OUT;  
                } else {  
                    currentStatus = STATUS_ZOOM_IN;  
                }  
                // 进行缩放倍数检查，最大只允许将图片放大4倍，最小可以缩小到初始化比例  
                if ((currentStatus == STATUS_ZOOM_OUT && totalRatio < 4 * initRatio)  
                        || (currentStatus == STATUS_ZOOM_IN && totalRatio > initRatio)) {  
                    scaledRatio = (float) (fingerDis / lastFingerDis);  
                    totalRatio = totalRatio * scaledRatio;
                    if (totalRatio > 4 * initRatio) {  
                        totalRatio = 4 * initRatio;  
                    } else if (totalRatio < initRatio) {  
                        totalRatio = initRatio;  
                    }  
                    // 调用onDraw()方法绘制图片  
                    invalidate();  
                    lastFingerDis = fingerDis;  
                }
            }
            break;
        case MotionEvent.ACTION_POINTER_UP:
            if (event.getPointerCount() == 2) {  
                // 手指离开屏幕时将临时值还原  
                lastXMove = -1;  
                lastYMove = -1;  
            }  
            break;  
        case MotionEvent.ACTION_UP:  
            // 手指离开屏幕时将临时值还原  
            lastXMove = -1;  
            lastYMove = -1; 
            //Time t=new Time();
            //t.setToNow();
            long t=Calendar.getInstance().getTimeInMillis();
            if(t-mStartTime>=100){
                break;
            }
            float fX=event.getX();
            float fY=event.getY();
            mFaceClicked=null;
            for(Face f:mFaces){
                Rect faceRect=f.getFaceRect();
                float left=faceRect.x*totalRatio/mInSampleSize+totalTranslateX;
                float top=faceRect.y*totalRatio/mInSampleSize+totalTranslateY;
                float right=(faceRect.x+faceRect.width)*totalRatio/mInSampleSize+totalTranslateX;
                float bottom=(faceRect.y+faceRect.height)*totalRatio/mInSampleSize+totalTranslateY;
                if(fX>=left&&fX<=right&&
                        fY>=top&&fY<=bottom){
                    mFaceClicked=f;
                }
            }
            final Face face=mFaceClicked;
            if(face==null)
                break;
            invalidate();

            if(face.getPeopleName()==null){

                final EditText mText = new EditText(
                        getContext());
                AlertDialog.Builder builder = new AlertDialog.Builder(
                        getContext());
                builder.setTitle("请输入名字")
                .setIcon(
                        android.R.drawable.ic_dialog_info)
                .setView(mText)
                .setPositiveButton(
                        "确定",
                        new DialogInterface.OnClickListener() {
                            @Override
                            public void onClick(
                                    DialogInterface dialog,
                                    int which) {
                                FaceRecManagerSingleInstance.getInstance(getContext()).update(
                                        face.getFaceId(),
                                        mText.getText()
                                                .toString());
                                invalidate();
                            }
                        })
                .setNegativeButton("取消", null).show();
            }else{
                AlertDialog.Builder builder = new AlertDialog.Builder(
                        getContext());
                builder.setMessage("这是 " + face.getPeopleName() + " 吗？")
                .setIcon(
                        android.R.drawable.ic_dialog_info)
                .setPositiveButton(
                        "是",
                        new DialogInterface.OnClickListener() {
                            @Override
                            public void onClick(
                                    DialogInterface dialog,
                                    int which) {
                                FaceRecManagerSingleInstance.getInstance(getContext()).update(
                                        face.getFaceId(),
                                        face.getPeopleName());
                                invalidate();
                            }
                        })
                .setNegativeButton(
                        "不是",
                        new DialogInterface.OnClickListener() {
                            @Override
                            public void onClick(
                                    DialogInterface dialog,
                                    int which) {
                                final EditText mText = new EditText(
                                        getContext());
                                AlertDialog.Builder builder = new AlertDialog.Builder(
                                        getContext());                              
                                builder.setTitle(
                                        "请输入名字")
                                        .setIcon(android.R.drawable.ic_dialog_info)
                                        .setView(mText)
                                        .setPositiveButton(
                                                "确定",
                                                new DialogInterface.OnClickListener() {
                                                    @Override
                                                    public void onClick(
                                                            DialogInterface dialog,
                                                            int which) {
                                                        FaceRecManagerSingleInstance.getInstance(getContext())
                                                                .update(face.getFaceId(),mText.getText().toString());
                                                        invalidate();
                                                    }
                                        })
                                        .setNegativeButton("取消",null)
                                        .show();
                            }
                        }).show();
            } 
            break;  
        default:  
            break;     
        }

        return true;
    }

    public Bitmap getSrcBitmap(){
        return sourceBitmap;
    }

    private void drawFaces(Canvas canvas){
        Log.d(TAG,"drawFaces");
        for(Face face:mFaces){
            Rect faceRect=face.getFaceRect();
            float left=faceRect.x*totalRatio/mInSampleSize+totalTranslateX;
            float top=faceRect.y*totalRatio/mInSampleSize+totalTranslateY;
            float right=(faceRect.x+faceRect.width)*totalRatio/mInSampleSize+totalTranslateX;
            float bottom=(faceRect.y+faceRect.height)*totalRatio/mInSampleSize+totalTranslateY;
            if(!face.getVerified()){
                mPaint.setColor(Color.GREEN);
            }
            if(face.equals(mFaceClicked)){
                mPaint.setColor(Color.YELLOW);
                mFaceClicked=null;
            }
            canvas.drawRect(left,top,right,bottom, mPaint);
            if(face.getPeopleName()!=null){
                mPaint.setTextSize((float) ((right-left)*0.15));
                mPaint.setStrokeWidth(0);
                canvas.drawText(face.getPeopleName(),left ,top-4, mPaint);
                mPaint.setStrokeWidth(2);
            }
            mPaint.setColor(Color.WHITE);
        }
    }
    /** 
     * 根据currentStatus的值来决定对图片进行什么样的绘制操作。 
     */  
    @Override  
    protected void onDraw(Canvas canvas) {  
        try{    
            super.onDraw(canvas);
            switch (currentStatus) {  
            case STATUS_ZOOM_OUT:  
            case STATUS_ZOOM_IN:  
                zoom(canvas);  
                break;
            case STATUS_MOVE:  
                move(canvas);  
                break;  
            case STATUS_INIT:  
                initBitmap(canvas);  
            default:  
                canvas.drawBitmap(sourceBitmap, matrix, null);
                drawFaces(canvas);
                break;  
            }
        }catch(Exception e){
            Log.e(TAG,"Error in onDraw:",e);
        }
    }

    /** 
     * 对图片进行缩放处理。 
     *  
     * @param canvas 
     */  
    private void zoom(Canvas canvas) {  
        matrix.reset();  
        // 将图片按总缩放比例进行缩放  
        matrix.postScale(totalRatio, totalRatio);  
        float scaledWidth = sourceBitmap.getWidth() * totalRatio;  
        float scaledHeight = sourceBitmap.getHeight() * totalRatio;  
        float translateX = 0f;  
        float translateY = 0f;  
        // 如果当前图片宽度小于屏幕宽度，则按屏幕中心的横坐标进行水平缩放。
        //否则按两指的中心点的横坐标进行水平缩放
        if (currentBitmapWidth < width) {  
            translateX = (width - scaledWidth) / 2f;  
        } else {  
            translateX = totalTranslateX * scaledRatio + centerPointX * (1 - scaledRatio);  
            // 进行边界检查，保证图片缩放后在水平方向上不会偏移出屏幕  
            if (translateX > 0) {  
                translateX = 0;  
            } else if (width - translateX > scaledWidth) {  
                translateX = width - scaledWidth;  
            }  
        } 
     // 如果当前图片高度小于屏幕高度，则按屏幕中心的纵
     //坐标进行垂直缩放。否则按两指的中心点的纵坐标进行垂直缩放
        if (currentBitmapHeight < height) {  
            translateY = (height - scaledHeight) / 2f;  
        }else{
            translateY = totalTranslateY * scaledRatio + centerPointY * (1 - scaledRatio);  
            // 进行边界检查，保证图片缩放后在垂直方向上不会偏移出屏幕  
            if (translateY > 0) {  
                translateY = 0;  
            } else if (height - translateY > scaledHeight) {  
                translateY = height - scaledHeight;  
            }  
        }
        // 缩放后对图片进行偏移，以保证缩放后中心点位置不变  
        matrix.postTranslate(translateX, translateY);  
        totalTranslateX = translateX;  
        totalTranslateY = translateY;  
        currentBitmapWidth = scaledWidth;  
        currentBitmapHeight = scaledHeight;  
        canvas.drawBitmap(sourceBitmap, matrix, null);  
        drawFaces(canvas);
    }

    /** 
     * 对图片进行平移处理 
     *  
     * @param canvas 
     */  
    private void move(Canvas canvas) {  
        matrix.reset(); 
        // 根据手指移动的距离计算出总偏移值  
        float translateX = totalTranslateX + movedDistanceX;  
        float translateY = totalTranslateY + movedDistanceY;  
        // 先按照已有的缩放比例对图片进行缩放  
        matrix.postScale(totalRatio, totalRatio);  
        // 再根据移动距离进行偏移  
        matrix.postTranslate(translateX, translateY);  
        totalTranslateX = translateX;  
        totalTranslateY = translateY;  
        canvas.drawBitmap(sourceBitmap, matrix, null);  
        drawFaces(canvas);
    }

    /** 
     * 对图片进行初始化操作，包括让图片居中，以及当图片大于屏幕宽高时对图片进行压缩。 
     *  
     * @param canvas 
     */  
    private void initBitmap(Canvas canvas) {  
        if (sourceBitmap != null) {  
            matrix.reset(); 
            int bitmapWidth = sourceBitmap.getWidth();  
            int bitmapHeight = sourceBitmap.getHeight();  
            if (bitmapWidth > width || bitmapHeight > height) {  
                if (bitmapWidth - width > bitmapHeight - height) {  
                    // 当图片宽度大于屏幕宽度时，将图片等比例压缩，使它可以完全显示出来  
                    float ratio = width / (bitmapWidth * 1.0f);  
                    matrix.postScale(ratio, ratio);  
                    float translateY = (height - (bitmapHeight * ratio)) / 2f;  
                    // 在纵坐标方向上进行偏移，以保证图片居中显示  
                    matrix.postTranslate(0, translateY);  
                    totalTranslateY = translateY;  
                    totalRatio = initRatio = ratio;  
                }else {  
                    // 当图片高度大于屏幕高度时，将图片等比例压缩，使它可以完全显示出来  
                    float ratio = height / (bitmapHeight * 1.0f);  
                    matrix.postScale(ratio, ratio);  
                    float translateX = (width - (bitmapWidth * ratio)) / 2f;  
                    // 在横坐标方向上进行偏移，以保证图片居中显示  
                    matrix.postTranslate(translateX, 0);  
                    totalTranslateX = translateX;  
                    totalRatio = initRatio = ratio;  
                }
                currentBitmapWidth = bitmapWidth * initRatio;  
                currentBitmapHeight = bitmapHeight * initRatio;
            }else{
                // 当图片的宽高都小于屏幕宽高时，直接让图片居中显示  
                float translateX = (width - sourceBitmap.getWidth()) / 2f;  
                float translateY = (height - sourceBitmap.getHeight()) / 2f;  
                matrix.postTranslate(translateX, translateY);  
                totalTranslateX = translateX;  
                totalTranslateY = translateY;  
                totalRatio = initRatio = 1f;  
                currentBitmapWidth = bitmapWidth;  
                currentBitmapHeight = bitmapHeight;  
            }
            canvas.drawBitmap(sourceBitmap, matrix, null); 
            drawFaces(canvas);
        }           
    }


     /** 
     * 计算两个手指之间的距离。 
     *  
     * @param event 
     * @return 两个手指之间的距离 
     */  
    private double distanceBetweenFingers(MotionEvent event) {  
        float disX = Math.abs(event.getX(0) - event.getX(1));  
        float disY = Math.abs(event.getY(0) - event.getY(1));  
        return Math.sqrt(disX * disX + disY * disY);  
    }  

    /** 
     * 计算两个手指之间中心点的坐标。 
     *  
     * @param event 
     */  
    private void centerPointBetweenFingers(MotionEvent event) {  
        float xPoint0 = event.getX(0);  
        float yPoint0 = event.getY(0);  
        float xPoint1 = event.getX(1);  
        float yPoint1 = event.getY(1);  
        centerPointX = (xPoint0 + xPoint1) / 2;  
        centerPointY = (yPoint0 + yPoint1) / 2;  
    }  
}

存在的问题

瀑布流渲染似乎有点慢，要等很久的样子。有时候闪退。