杂家前文曾写过一篇关于只拍摄特定区域图片的demo，只是比较简陋，在坐标的换算上不是很严谨，而且没有完成预览界面四周暗中间亮的效果，深以为憾，今天把这个补齐了。

在上代码之前首先交代下，这里面存在着换算的两种模式。第一种，是以屏幕上的矩形区域为基准进行换算。举个例子，屏幕中间一个 矩形框为100dip*100dip.这里一定要使用dip为单位，否则在不同的手机上屏幕呈现的矩形框大小不一样。先将这个dip换算成px，然后根据屏幕的宽和高的像素计算出矩形区域，传给Surfaceview上铺的一层View，这里叫MaskView(蒙板),让MaskView进行绘制。然后拍照时，通过屏幕矩形框的大小和屏幕的大小与最终拍摄图片的PictureSize进行换算，得到图片里的矩形区域图片，然后截取保存。第二种模式是，预先知道想要的图片的长宽，如我就是想截400*400（单位为px）大小的图片。那就以此为基准，换算出屏幕上呈现的Rect的长宽，然后让MaskView绘制。究竟用哪一种模式，按需选择。本文以第一种模式示例。下面上代码:

在杂家的前文基础上进行封装，首先封装一个MaskView,用来绘制四周暗中间亮的效果，或者你可以加一个滚动条，这都不是事。

一、MaskView.java

package org.yanzi.ui;import org.yanzi.util.DisplayUtil;import android.content.Context;import android.graphics.Canvas;import android.graphics.Color;import android.graphics.Paint;import android.graphics.Paint.Style;import android.graphics.Point;import android.graphics.Rect;import android.util.AttributeSet;import android.util.Log;import android.widget.ImageView;public class MaskView extends ImageView {	private static final String TAG = "YanZi";	private Paint mLinePaint;	private Paint mAreaPaint;	private Rect mCenterRect = null;	private Context mContext;	public MaskView(Context context, AttributeSet attrs) {		super(context, attrs);		// TODO Auto-generated constructor stub		initPaint();		mContext = context;		Point p	= DisplayUtil.getScreenMetrics(mContext);		widthScreen = p.x;		heightScreen = p.y;	}	private void initPaint(){		//绘制中间透明区域矩形边界的Paint		mLinePaint = new Paint(Paint.ANTI_ALIAS_FLAG);		mLinePaint.setColor(Color.BLUE);		mLinePaint.setStyle(Style.STROKE);		mLinePaint.setStrokeWidth(5f);		mLinePaint.setAlpha(30);		//绘制四周阴影区域		mAreaPaint = new Paint(Paint.ANTI_ALIAS_FLAG);		mAreaPaint.setColor(Color.GRAY);		mAreaPaint.setStyle(Style.FILL);		mAreaPaint.setAlpha(180);							}	public void setCenterRect(Rect r){		Log.i(TAG, "setCenterRect...");		this.mCenterRect = r;		postInvalidate();	}	public void clearCenterRect(Rect r){		this.mCenterRect = null;	}	int widthScreen, heightScreen;	@Override	protected void onDraw(Canvas canvas) {		// TODO Auto-generated method stub		Log.i(TAG, "onDraw...");		if(mCenterRect == null)			return;		//绘制四周阴影区域		canvas.drawRect(0, 0, widthScreen, mCenterRect.top, mAreaPaint);		canvas.drawRect(0, mCenterRect.bottom + 1, widthScreen, heightScreen, mAreaPaint);		canvas.drawRect(0, mCenterRect.top, mCenterRect.left - 1, mCenterRect.bottom  + 1, mAreaPaint);		canvas.drawRect(mCenterRect.right + 1, mCenterRect.top, widthScreen, mCenterRect.bottom + 1, mAreaPaint);		//绘制目标透明区域		canvas.drawRect(mCenterRect, mLinePaint);		super.onDraw(canvas);	}}

1、为了让这个MaskView有更好的适配型，里面设置变量mCenterRect，这个矩阵的坐标就是已经换算好的，对屏幕的尺寸进行适配过的，以全屏下的屏幕宽高为坐标系，不需要再换算了。

2、当然这个MaskView是全屏的，这里修改下PlayCamera_V1.0.0中的一个小问题,我将它的布局换成如下:

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"    xmlns:tools="http://schemas.android.com/tools"    android:layout_width="match_parent"    android:layout_height="match_parent"    tools:context=".CameraActivity" >    <FrameLayout        android:layout_width="match_parent"        android:layout_height="match_parent" >        <org.yanzi.camera.preview.CameraSurfaceView            android:id="@+id/camera_surfaceview"            android:layout_width="0dip"            android:layout_height="0dip" />        <org.yanzi.ui.MaskView            android:id="@+id/view_mask"            android:layout_width="match_parent"            android:layout_height="match_parent" />    </FrameLayout>    <ImageButton        android:id="@+id/btn_shutter"        android:layout_width="wrap_content"        android:layout_height="wrap_content"        android:layout_alignParentBottom="true"        android:layout_centerHorizontal="true"        android:layout_marginBottom="10dip"        android:background="@drawable/btn_shutter_background" /></RelativeLayout>

3.关于绘制阴影区域的代码里的+1 -1这几个小地方尽量不要错，按本文写就不会错。顺序是先绘制最上面、最下面、左侧、右侧四个区域的阴影。

//绘制四周阴影区域		canvas.drawRect(0, 0, widthScreen, mCenterRect.top, mAreaPaint);		canvas.drawRect(0, mCenterRect.bottom + 1, widthScreen, heightScreen, mAreaPaint);		canvas.drawRect(0, mCenterRect.top, mCenterRect.left - 1, mCenterRect.bottom  + 1, mAreaPaint);		canvas.drawRect(mCenterRect.right + 1, mCenterRect.top, widthScreen, mCenterRect.bottom + 1, mAreaPaint);

二、在CameraActivity.java里封装两个函数:

	/**生成拍照后图片的中间矩形的宽度和高度	 * @param w 屏幕上的矩形宽度，单位px	 * @param h 屏幕上的矩形高度，单位px	 * @return	 */	private Point createCenterPictureRect(int w, int h){				int wScreen = DisplayUtil.getScreenMetrics(this).x;		int hScreen = DisplayUtil.getScreenMetrics(this).y;		int wSavePicture = CameraInterface.getInstance().doGetPrictureSize().y; //因为图片旋转了，所以此处宽高换位		int hSavePicture = CameraInterface.getInstance().doGetPrictureSize().x; //因为图片旋转了，所以此处宽高换位		float wRate = (float)(wSavePicture) / (float)(wScreen);		float hRate = (float)(hSavePicture) / (float)(hScreen);		float rate = (wRate <= hRate) ? wRate : hRate;//也可以按照最小比率计算				int wRectPicture = (int)( w * wRate);		int hRectPicture = (int)( h * hRate);		return new Point(wRectPicture, hRectPicture);			}	/**	 * 生成屏幕中间的矩形	 * @param w 目标矩形的宽度,单位px	 * @param h	目标矩形的高度,单位px	 * @return	 */	private Rect createCenterScreenRect(int w, int h){		int x1 = DisplayUtil.getScreenMetrics(this).x / 2 - w / 2;		int y1 = DisplayUtil.getScreenMetrics(this).y / 2 - h / 2;		int x2 = x1 + w;		int y2 = y1 + h;		return new Rect(x1, y1, x2, y2);	}

三、在开启预览后，就可以让MaskView绘制了

	@Override	public void cameraHasOpened() {		// TODO Auto-generated method stub		SurfaceHolder holder = surfaceView.getSurfaceHolder();		CameraInterface.getInstance().doStartPreview(holder, previewRate);		if(maskView != null){			Rect screenCenterRect = createCenterScreenRect(DisplayUtil.dip2px(this, DST_CENTER_RECT_WIDTH)					,DisplayUtil.dip2px(this, DST_CENTER_RECT_HEIGHT));			maskView.setCenterRect(screenCenterRect);		}	}

	public void setCenterRect(Rect r){		Log.i(TAG, "setCenterRect...");		this.mCenterRect = r;		postInvalidate();	}

四、最后就是告诉拍照的回调了

private class BtnListeners implements OnClickListener{		@Override		public void onClick(View v) {			// TODO Auto-generated method stub			switch(v.getId()){			case R.id.btn_shutter:				if(rectPictureSize == null){					rectPictureSize = createCenterPictureRect(DisplayUtil.dip2px(CameraActivity.this, DST_CENTER_RECT_WIDTH)							,DisplayUtil.dip2px(CameraActivity.this, DST_CENTER_RECT_HEIGHT));				}				CameraInterface.getInstance().doTakePicture(rectPictureSize.x, rectPictureSize.y);				break;			default:break;			}		}	}

	int DST_RECT_WIDTH, DST_RECT_HEIGHT;	public void doTakePicture(int w, int h){		if(isPreviewing && (mCamera != null)){			Log.i(TAG, "矩形拍照尺寸:width = " + w + " h = " + h);			DST_RECT_WIDTH = w;			DST_RECT_HEIGHT = h;			mCamera.takePicture(mShutterCallback, null, mRectJpegPictureCallback);		}	}

/**	 * 拍摄指定区域的Rect	 */	PictureCallback mRectJpegPictureCallback = new PictureCallback() 	//对jpeg图像数据的回调,最重要的一个回调	{		public void onPictureTaken(byte[] data, Camera camera) {			// TODO Auto-generated method stub			Log.i(TAG, "myJpegCallback:onPictureTaken...");			Bitmap b = null;			if(null != data){				b = BitmapFactory.decodeByteArray(data, 0, data.length);//data是字节数据，将其解析成位图				mCamera.stopPreview();				isPreviewing = false;			}			//保存图片到sdcard			if(null != b)			{				//设置FOCUS_MODE_CONTINUOUS_VIDEO)之后，myParam.set("rotation", 90)失效。				//图片竟然不能旋转了，故这里要旋转下				Bitmap rotaBitmap = ImageUtil.getRotateBitmap(b, 90.0f);				int x = rotaBitmap.getWidth()/2 - DST_RECT_WIDTH/2;				int y = rotaBitmap.getHeight()/2 - DST_RECT_HEIGHT/2;				Log.i(TAG, "rotaBitmap.getWidth() = " + rotaBitmap.getWidth()						+ " rotaBitmap.getHeight() = " + rotaBitmap.getHeight());				Bitmap rectBitmap = Bitmap.createBitmap(rotaBitmap, x, y, DST_RECT_WIDTH, DST_RECT_HEIGHT);				FileUtil.saveBitmap(rectBitmap);				if(rotaBitmap.isRecycled()){					rotaBitmap.recycle();					rotaBitmap = null;				}				if(rectBitmap.isRecycled()){					rectBitmap.recycle();					rectBitmap = null;				}			}			//再次进入预览			mCamera.startPreview();			isPreviewing = true;			if(!b.isRecycled()){				b.recycle();				b = null;			}		}	};

注意事项:

1、为了让截出的区域和屏幕上显示的完全一致，这里首先要满足PreviewSize长宽比、PictureSize长宽比、屏幕预览Surfaceview的长宽比为同一比例，这是个先决条件。然后再将屏幕矩形区域长宽换算成图片矩形区域时:

/**生成拍照后图片的中间矩形的宽度和高度
* @param w 屏幕上的矩形宽度，单位px
* @param h 屏幕上的矩形高度，单位px
* @return
*/
private Point createCenterPictureRect(int w, int h){

int wScreen = DisplayUtil.getScreenMetrics(this).x;
int hScreen = DisplayUtil.getScreenMetrics(this).y;
int wSavePicture = CameraInterface.getInstance().doGetPrictureSize().y; //因为图片旋转了，所以此处宽高换位
int hSavePicture = CameraInterface.getInstance().doGetPrictureSize().x; //因为图片旋转了，所以此处宽高换位
float wRate = (float)(wSavePicture) / (float)(wScreen);
float hRate = (float)(hSavePicture) / (float)(hScreen);
float rate = (wRate <= hRate) ? wRate : hRate;//也可以按照最小比率计算

int wRectPicture = (int)( w * wRate);
int hRectPicture = (int)( h * hRate);
return new Point(wRectPicture, hRectPicture);

}

原则上wRate 是应该等于hRate 的！！！！！！！！！！

2、我对CamParaUtil里的getPropPreviewSize和getPropPictureSize进行了更新，以前是以width进行判断的，这里改成了以height进行判断。因为在读取参数时得到的是800*480(宽*高)这种类型，一般高是稍微小的，所以以height进行判断。而这个高在最终显示和保存时经过旋转又成了宽。

	public Size getPropPictureSize(List<Camera.Size> list, float th, int minHeight){		Collections.sort(list, sizeComparator);		int i = 0;		for(Size s:list){			if((s.height >= minHeight) && equalRate(s, th)){				Log.i(TAG, "PictureSize : w = " + s.width + "h = " + s.height);				break;			}			i++;		}		if(i == list.size()){			i = 0;//如果没找到，就选最小的size		}		return list.get(i);	}

			//设置PreviewSize和PictureSize			Size pictureSize = CamParaUtil.getInstance().getPropPictureSize(					mParams.getSupportedPictureSizes(),previewRate, 1300);			mParams.setPictureSize(pictureSize.width, pictureSize.height);			Size previewSize = CamParaUtil.getInstance().getPropPreviewSize(					mParams.getSupportedPreviewSizes(), previewRate, 400);			mParams.setPreviewSize(previewSize.width, previewSize.height);