Android在相机预览上绘制

Question

我正在制作一个虚拟现实应用程序,摄像机应该检测到面部,找到它们并在摄像机预览中显示它们的位置.

我知道有3种方法可以做到,我想尽可能快地使用GLSurfaceView(根据这篇文章),但是目前我正在尝试使用相机用于预览的相同 SurfaceView.我的回调onFaceDetection就是这样:

public class MyActivity extends Activity implements SurfaceHolder.Callback, Camera.FaceDetectionListener {
    Camera camera;
    SurfaceView svPreview;
    SurfaceHolder previewHolder;
    TextView tvInfo;
    Paint red;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);

        svPreview = (SurfaceView) findViewById(R.id.svPreview);
        tvInfo = (TextView) findViewById(R.id.tvInfo);

        red = new Paint();
        red.setStyle(Paint.Style.STROKE);
        red.setStrokeWidth(3);

        previewHolder = svPreview.getHolder();
        previewHolder.addCallback(this);
        previewHolder.setType(SurfaceHolder.SURFACE_TYPE_PUSH_BUFFERS);
    }

    public void surfaceCreated(SurfaceHolder arg0) {
        camera = Camera.open();
        try {
            camera.setDisplayOrientation(90);
            camera.setFaceDetectionListener(this);
            camera.setPreviewDisplay(previewHolder);
        }
        catch (IOException e) {
            e.printStackTrace();
        }
    }

    public void surfaceChanged(SurfaceHolder holder, int format, int width, int height) {
        // . . .
        camera.startPreview();
        camera.autoFocus(null);
        camera.startFaceDetection();
    }

    public void surfaceDestroyed(SurfaceHolder arg0) {
        camera.stopFaceDetection();
        camera.cancelAutoFocus();
        camera.stopPreview();
        camera.release();
        camera = null;
    }

    public void onFaceDetection(Face[] faces, Camera camera) {  
        tvInfo.setText("Faces: " + String.valueOf(faces.length));

        Canvas canvas = previewHolder.lockCanvas();
        for(int i=0; i < faces.length; i++) {
            Point leftEye = faces[i].leftEye;
            Point rightEye = faces[i].rightEye;
            // this is not working
            canvas.drawPoint(leftEye.x, leftEye.y, red);
        }
        previewHolder.unlockCanvasAndPost(canvas);
    }
}

使用此代码,我不断收到此错误:

09-03 19:35:42.743: E/SurfaceHolder(19394): Exception locking surface
09-03 19:35:42.743: E/SurfaceHolder(19394): java.lang.IllegalArgumentException
09-03 19:35:42.743: E/SurfaceHolder(19394):     at android.view.Surface.lockCanvasNative(Native Method)
09-03 19:35:42.743: E/SurfaceHolder(19394):     at android.view.Surface.lockCanvas(Surface.java:76)
09-03 19:35:42.743: E/SurfaceHolder(19394):     at android.view.SurfaceView$4.internalLockCanvas(SurfaceView.java:744)
09-03 19:35:42.743: E/SurfaceHolder(19394):     at android.view.SurfaceView$4.lockCanvas(SurfaceView.java:720)
09-03 19:35:42.743: E/SurfaceHolder(19394):     at com.bluetooth.activities.MyActivity.onFaceDetection(MyActivity.java:90)
09-03 19:35:42.743: E/SurfaceHolder(19394):     at android.hardware.Camera$EventHandler.handleMessage(Camera.java:729)
09-03 19:35:42.743: E/SurfaceHolder(19394):     at android.os.Handler.dispatchMessage(Handler.java:99)
09-03 19:35:42.743: E/SurfaceHolder(19394):     at android.os.Looper.loop(Looper.java:137)
09-03 19:35:42.743: E/SurfaceHolder(19394):     at android.app.ActivityThread.main(ActivityThread.java:4424)
09-03 19:35:42.743: E/SurfaceHolder(19394):     at java.lang.reflect.Method.invokeNative(Native Method)
09-03 19:35:42.743: E/SurfaceHolder(19394):     at java.lang.reflect.Method.invoke(Method.java:511)
09-03 19:35:42.743: E/SurfaceHolder(19394):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784)
09-03 19:35:42.743: E/SurfaceHolder(19394):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551)
09-03 19:35:42.743: E/SurfaceHolder(19394):     at dalvik.system.NativeStart.main(Native Method)
09-03 19:35:42.743: W/dalvikvm(19394): threadid=1: thread exiting with uncaught exception (group=0x40a561f8)
09-03 19:35:42.766: E/AndroidRuntime(19394): FATAL EXCEPTION: main
09-03 19:35:42.766: E/AndroidRuntime(19394): java.lang.IllegalArgumentException
09-03 19:35:42.766: E/AndroidRuntime(19394):    at android.view.Surface.unlockCanvasAndPost(Native Method)
09-03 19:35:42.766: E/AndroidRuntime(19394):    at android.view.SurfaceView$4.unlockCanvasAndPost(SurfaceView.java:775)
09-03 19:35:42.766: E/AndroidRuntime(19394):    at com.bluetooth.activities.MyActivity.onFaceDetection(MyActivity.java:99)
09-03 19:35:42.766: E/AndroidRuntime(19394):    at android.hardware.Camera$EventHandler.handleMessage(Camera.java:729)
09-03 19:35:42.766: E/AndroidRuntime(19394):    at android.os.Handler.dispatchMessage(Handler.java:99)
09-03 19:35:42.766: E/AndroidRuntime(19394):    at android.os.Looper.loop(Looper.java:137)
09-03 19:35:42.766: E/AndroidRuntime(19394):    at android.app.ActivityThread.main(ActivityThread.java:4424)
09-03 19:35:42.766: E/AndroidRuntime(19394):    at java.lang.reflect.Method.invokeNative(Native Method)
09-03 19:35:42.766: E/AndroidRuntime(19394):    at java.lang.reflect.Method.invoke(Method.java:511)
09-03 19:35:42.766: E/AndroidRuntime(19394):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784)
09-03 19:35:42.766: E/AndroidRuntime(19394):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551)
09-03 19:35:42.766: E/AndroidRuntime(19394):    at dalvik.system.NativeStart.main(Native Method)

相机试图在同一SurfaceView上绘制预览面部检测回调是否有问题？如何在不分层SurfaceView的情况下执行此操作？

Answer 1

不能锁定并绘制在SurfaceView其中有Type.PUSH_BUFFERS,(一个你要显示的帧).您必须在Z方向上创建原始视图上方的另一个视图,并SurfaceView在其中绘制View.

因此,在您main.xml的原始视图下创建一个自定义视图FrameLayout.

SurfaceView在您的活动视图中创建和处理a .将此视图添加到"相机"预览显示中.传递自定义视图SurfaceHolder.在此视图中,您可以在画布上锁定和绘制.

Answer 2

正如James指出你需要创建扩展SurfaceView的自定义表面(我通常也实现SurfaceHolder.Callback):

public class CameraSurfacePreview extends SurfaceView implements SurfaceHolder.Callback

构造函数将是这样的:

public CameraSurfacePreview(Context context) {
     super(context);
     ...
     mHolder = getHolder();
     mHolder.setType(SurfaceHolder.SURFACE_TYPE_PUSH_BUFFERS);
     ...

在相机打开调用后,你需要将相机与表面绑定(如果你实现了SurfaceHolder.Callback实现了将它放在重写的surfaceCreated中):

mCamera = Camera.open();
mCamera.setPreviewDisplay(mHolder);

最后,您需要在活动内容视图中添加自定义曲面的实例:

CameraSurfacePreview cameraSurfacePreview = new CameraSurfacePreview(this);
//camera surface preview is first child!
((ViewGroup)findViewById(R.id.cameraLayout)).addView(cameraSurfacePreview, 0); 

在我的示例中,活动的布局看起来像(我在主框架布局中显示相机预览):

<?xml version="1.0" encoding="utf-8"?>
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android" 
              android:layout_width="fill_parent"        
                      android:layout_height="fill_parent" 
              android:layout_gravity="top|left"
              android:id="@+id/cameraLayout">