最近在从零开始写一个移动端的AR系统，坑实在是太多了！！！整个项目使用了OpenCV第三方库，但对于摄像机来说，和原生Camera的方法基本相同。

以OpenCV的JavaCameraView为例，首先需要定制自己的Camera，主要代码如下：

import java.util.ArrayList;

import java.util.List;

import org.opencv.android.JavaCameraView;

import android.R.integer;

import android.content.Context;

import android.graphics.Rect;

import android.graphics.RectF;

import android.hardware.Camera;

import android.hardware.Camera.AutoFocusCallback;

import android.util.AttributeSet;

import android.view.MotionEvent;

import android.widget.Toast;

public class MTCameraView extends JavaCameraView implements AutoFocusCallback {

	public MTCameraView(Context context, int attrs) {

		super(context, attrs);

		// TODO Auto-generated constructor stub

	}

	public List<Camera.Size> getResolutionList() {

	    return  mCamera.getParameters().getSupportedPreviewSizes();

	}

	public Camera.Size getResolution() {

	    Camera.Parameters params = mCamera.getParameters();

	    Camera.Size s = params.getPreviewSize();

	    return s;

	}

	public void setResolution(Camera.Size resolution) {

	    disconnectCamera();

	    connectCamera((int)resolution.width, (int)resolution.height);

	}

	public void focusOnTouch(MotionEvent event) {

        Rect focusRect = calculateTapArea(event.getRawX(), event.getRawY(), 1f);

        Rect meteringRect = calculateTapArea(event.getRawX(), event.getRawY(), 1.5f);

        Camera.Parameters parameters = mCamera.getParameters();

        parameters.setFocusMode(Camera.Parameters.FOCUS_MODE_AUTO);

        if (parameters.getMaxNumFocusAreas() > 0) {

        	List<Camera.Area> focusAreas = new ArrayList<Camera.Area>();

        	focusAreas.add(new Camera.Area(focusRect, 1000));

        	parameters.setFocusAreas(focusAreas);

        }

        if (parameters.getMaxNumMeteringAreas() > 0) {

        	List<Camera.Area> meteringAreas = new ArrayList<Camera.Area>();

        	meteringAreas.add(new Camera.Area(meteringRect, 1000));

            parameters.setMeteringAreas(meteringAreas);

        }

        mCamera.setParameters(parameters);

        mCamera.autoFocus(this);

	}

	/**

	 * Convert touch position x:y to {@link Camera.Area} position -1000:-1000 to 1000:1000.

	 */

	private Rect calculateTapArea(float x, float y, float coefficient) {

	    float focusAreaSize = 300;

	    int areaSize = Float.valueOf(focusAreaSize * coefficient).intValue();

	    int centerX = (int) (x / getResolution().width * 2000 - 1000);

	    int centerY = (int) (y / getResolution().height * 2000 - 1000);

	    int left = clamp(centerX - areaSize / 2, -1000, 1000);

	    int right = clamp(left + areaSize, -1000, 1000);

	    int top = clamp(centerY - areaSize / 2, -1000, 1000);

	    int bottom = clamp(top + areaSize, -1000, 1000);

	    return new Rect(left, top, right, bottom);

        }

	private int clamp(int x, int min, int max) {

	    if (x > max) {

	        return max;

	    }

	    if (x < min) {

	        return min;

	    }

	    return x;

	}

	public void setFocusMode (Context item, int type){

	    Camera.Parameters params = mCamera.getParameters();

	    List<String> FocusModes = params.getSupportedFocusModes();

	    switch (type){

	    case 0:

	        if (FocusModes.contains(Camera.Parameters.FOCUS_MODE_AUTO))

	            params.setFocusMode(Camera.Parameters.FOCUS_MODE_AUTO);

	        else

	            Toast.makeText(item, "Auto Mode not supported", Toast.LENGTH_SHORT).show();

	        break;

	    case 1:

	        if (FocusModes.contains(Camera.Parameters.FOCUS_MODE_CONTINUOUS_VIDEO))

	            params.setFocusMode(Camera.Parameters.FOCUS_MODE_CONTINUOUS_VIDEO);

	        else

	            Toast.makeText(item, "Continuous Mode not supported", Toast.LENGTH_SHORT).show();

	        break;

	    case 2:

	        if (FocusModes.contains(Camera.Parameters.FOCUS_MODE_EDOF))

	            params.setFocusMode(Camera.Parameters.FOCUS_MODE_EDOF);

	        else

	            Toast.makeText(item, "EDOF Mode not supported", Toast.LENGTH_SHORT).show();

	        break;

	    case 3:

	        if (FocusModes.contains(Camera.Parameters.FOCUS_MODE_FIXED))

	            params.setFocusMode(Camera.Parameters.FOCUS_MODE_FIXED);

	        else

	            Toast.makeText(item, "Fixed Mode not supported", Toast.LENGTH_SHORT).show();

	        break;

	    case 4:

	        if (FocusModes.contains(Camera.Parameters.FOCUS_MODE_INFINITY))

	            params.setFocusMode(Camera.Parameters.FOCUS_MODE_INFINITY);

	        else

	            Toast.makeText(item, "Infinity Mode not supported", Toast.LENGTH_SHORT).show();

	        break;

	    case 5:

	        if (FocusModes.contains(Camera.Parameters.FOCUS_MODE_MACRO))

	            params.setFocusMode(Camera.Parameters.FOCUS_MODE_MACRO);

	        else

	            Toast.makeText(item, "Macro Mode not supported", Toast.LENGTH_SHORT).show();

	        break;

	    }

	    mCamera.setParameters(params);

	}

	public void setFlashMode (Context item, int type){

	    Camera.Parameters params = mCamera.getParameters();

	    List<String> FlashModes = params.getSupportedFlashModes();

	    switch (type){

	    case 0:

	        if (FlashModes.contains(Camera.Parameters.FLASH_MODE_AUTO))

	            params.setFlashMode(Camera.Parameters.FLASH_MODE_AUTO);

	        else

	            Toast.makeText(item, "Auto Mode not supported", Toast.LENGTH_SHORT).show();

	        break;

	    case 1:

	        if (FlashModes.contains(Camera.Parameters.FLASH_MODE_OFF))

	            params.setFlashMode(Camera.Parameters.FLASH_MODE_OFF);

	        else

	            Toast.makeText(item, "Off Mode not supported", Toast.LENGTH_SHORT).show();

	        break;

	    case 2:

	        if (FlashModes.contains(Camera.Parameters.FLASH_MODE_ON))

	            params.setFlashMode(Camera.Parameters.FLASH_MODE_ON);

	        else

	            Toast.makeText(item, "On Mode not supported", Toast.LENGTH_SHORT).show();

	        break;

	    case 3:

	        if (FlashModes.contains(Camera.Parameters.FLASH_MODE_RED_EYE))

	            params.setFlashMode(Camera.Parameters.FLASH_MODE_RED_EYE);

	        else

	            Toast.makeText(item, "Red Eye Mode not supported", Toast.LENGTH_SHORT).show();

	        break;

	    case 4:

	        if (FlashModes.contains(Camera.Parameters.FLASH_MODE_TORCH))

	            params.setFlashMode(Camera.Parameters.FLASH_MODE_TORCH);

	        else

	            Toast.makeText(item, "Torch Mode not supported", Toast.LENGTH_SHORT).show();

	        break;

	    }

	    mCamera.setParameters(params);

	}

	@Override

	public void onAutoFocus(boolean arg0, Camera arg1) {

	}

}

在MainActivity中需要初始化MTCamera，并且实现OnTouchListener接口，以便在触摸屏幕时可以调用onTouch函数。其中主要代码如下：

	private MTCameraView mOpenCvCameraView;

	public void init() {

		mOpenCvCameraView = new MTCameraView(this, -1);

		mOpenCvCameraView.setCvCameraViewListener(this);

		mOpenCvCameraView.setFocusable(true);

		mOpenCvCameraView.setOnTouchListener(MainActivity.this);

		mOpenCvCameraView.enableView();

		FrameLayout frame = new FrameLayout(this);

		frame.addView(mOpenCvCameraView);

		setContentView(frame);

	     }

	@Override

	public boolean onTouch(View arg0, MotionEvent arg1) {

		// TODO Auto-generated method stub

		mOpenCvCameraView.focusOnTouch(arg1);

		return true;

	}

init()函数是自定义的初始化函数，可以在onCreate时使用。由于这里需要使用OpenCV库，所以本项目是在加载完OpenCV库并判断成功后才调用init()函数的。

在发生触摸事件时，MainActivity由于实现了OnTouchListener接口，因此会调用重写的onTouch函数，并把它的第二个参数MotionEvent传递给MTCamera，以便定位触摸位置。

MTCamera的focusOnTouch函数继续工作。它首先根据触摸位置计算对焦和测光（metering）区域的大小（通过calculateTapArea函数），然后创建新的Camera.Parameters，并设置摄像机的对焦模式为Auto。

然后，它分别判断该设备的相机是否支持设置对焦区域和测光区域，如果支持就分别为parameters设置之前计算好的聚焦和测光区域。

最后，让Camera自动对焦。

• calculateTapArea函数

  这个函数主要实现从屏幕坐标系到对焦坐标系的转换。由MotionEvent.getRowX()得到的是以屏幕坐标系（即屏幕左上角为原点，右下角为你的当前屏幕分辨率，单位是一个像素）为准的坐标，而setFocusAreas接受的List<Area>中的每一个Area的范围是（-1000，-1000）到（1000， 1000），也就是说屏幕中心为原点，左上角为（-1000，-1000），右下角为（1000，1000）。注意，如果超出这个范围的话，会报setParemeters failed的错误哦！除此之外，我们还提前定义了一个对焦框（测光框）的大小，并且接受一个参数（第三个参数coefficient）作为百分比进行调节。

至此完成了触摸对焦的功能。

但是，可以发现MTCamera里还有很大部分代码，主要是两个函数setFocusMode和setFlashMode。这两个函数，主要是因为在项目中我的图像经常是模糊的，但不知道系统支持那么对焦模式。这时，就可以使用这两个函数进行测试。这还需要在MainActivity中添加菜单栏的代码，以便进行选择。代码如下：

    private List<Camera.Size> mResolutionList;

    private MenuItem[] mResolutionMenuItems;

    private MenuItem[] mFocusListItems;

    private MenuItem[] mFlashListItems;

    private SubMenu mResolutionMenu;

    private SubMenu mFocusMenu;

    private SubMenu mFlashMenu;

    @Override

    public boolean onCreateOptionsMenu(Menu menu) {

        Log.i(TAG, "called onCreateOptionsMenu");

        List<String> mFocusList = new LinkedList<String>();

	    int idx =0;

	    mFocusMenu = menu.addSubMenu("Focus");

	    mFocusList.add("Auto");

	    mFocusList.add("Continuous Video");

	    mFocusList.add("EDOF");

	    mFocusList.add("Fixed");

	    mFocusList.add("Infinity");

	    mFocusList.add("Makro");

	    mFocusList.add("Continuous Picture");

	    mFocusListItems = new MenuItem[mFocusList.size()];

	    ListIterator<String> FocusItr = mFocusList.listIterator();

	    while(FocusItr.hasNext()){

	        // add the element to the mDetectorMenu submenu

	        String element = FocusItr.next();

	        mFocusListItems[idx] = mFocusMenu.add(2,idx,Menu.NONE,element);

	        idx++;

	    }

	    List<String> mFlashList = new LinkedList<String>();

	    idx = 0;

	    mFlashMenu = menu.addSubMenu("Flash");

	    mFlashList.add("Auto");

	    mFlashList.add("Off");

	    mFlashList.add("On");

	    mFlashList.add("Red-Eye");

	    mFlashList.add("Torch");

	    mFlashListItems = new MenuItem[mFlashList.size()];

	    ListIterator<String> FlashItr = mFlashList.listIterator();

	    while(FlashItr.hasNext()){

	        // add the element to the mDetectorMenu submenu

	        String element = FlashItr.next();

	        mFlashListItems[idx] = mFlashMenu.add(3,idx,Menu.NONE,element);

	        idx++;

	    }

	    mResolutionMenu = menu.addSubMenu("Resolution");

	    mResolutionList = mOpenCvCameraView.getResolutionList();

	    mResolutionMenuItems = new MenuItem[mResolutionList.size()];

	    ListIterator<Camera.Size> resolutionItr = mResolutionList.listIterator();

	    idx = 0;

	    while(resolutionItr.hasNext()) {

	        Camera.Size element = resolutionItr.next();

	        mResolutionMenuItems[idx] = mResolutionMenu.add(1, idx, Menu.NONE,

	                Integer.valueOf((int) element.width).toString() + "x" + Integer.valueOf((int) element.height).toString());

	        idx++;

	     }

	    return true;

    }

    public boolean onOptionsItemSelected(MenuItem item) {

        Log.i(TAG, "called onOptionsItemSelected; selected item: " + item);

        if (item.getGroupId() == 1)

	    {

	        int id = item.getItemId();

	        Camera.Size resolution = mResolutionList.get(id);

	        mOpenCvCameraView.setResolution(resolution);

	        resolution = mOpenCvCameraView.getResolution();

	        String caption = Integer.valueOf((int) resolution.width).toString() + "x" + Integer.valueOf((int) resolution.height).toString();

	        Toast.makeText(this, caption, Toast.LENGTH_SHORT).show();

	    }

	    else if (item.getGroupId()==2){

	       int focusType = item.getItemId();

	       mOpenCvCameraView.setFocusMode(this, focusType);

	    }

	    else if (item.getGroupId()==3){

	       int flashType = item.getItemId();

	       mOpenCvCameraView.setFlashMode(this, flashType);

	    }

        return true;

    }

这样运行后，点击菜单就可以看见有三个菜篮列表：Focus（对焦模式），Flash（视频模式），Resolution（支持的分辨率）。对焦模式和视频模式中提供了几种常见的模式供选择，代码会判断当前设备是否支持该模式。而分辨率菜单栏会显示出当前设备支持的所有分辨率种类。

• *上关于触摸对焦的讨论
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