无法在Android设备opencv java的中心绘制圆圈？

Question

I am trying to draw a circle on the screen such that it scales up on any android device irrespective of device size. But for some reason, I am unable to draw the circle exactly at the center of the screen. This is what I tried so far.

@Override
    public Mat onCameraFrame(CameraBridgeViewBase.CvCameraViewFrame inputFrame) {
        mrgba = inputFrame.rgba();
       // Imgproc.cvtColor(mrgba,mgray,Imgproc.COLOR_RGB2GRAY);
       // Imgproc.Canny(mgray,mcanny,50,150);
        DisplayMetrics displayMetrics = getResources().getDisplayMetrics();
        float dpHeight = displayMetrics.heightPixels / displayMetrics.density;
        float dpWidth = displayMetrics.widthPixels / displayMetrics.density;
        Imgproc.circle (
                mrgba,                 //Matrix obj of the image
                new Point(dpWidth*0.5,dpHeight*0.5),    //Center of the circle
                10,                    //Radius
                new Scalar(0, 0, 255),  //Scalar object for color
                10                     //Thickness of the circle
        );

        return mrgba;
    }

Circle image

Answer 1

To draw a circle on the center of screen with OpenCV don't use DisplayMetrics , but use Mat.height() and Mat.width() :

@Override
public Mat onCameraFrame(CameraBridgeViewBase.CvCameraViewFrame inputFrame) {
    mrgba = inputFrame.rgba();
    Imgproc.circle (
            mrgba,                 //Matrix obj of the image
            new Point(mrgba.width() * 0.5,mrgba.height() * 0.5),    //Center of the circle
            10,                    //Radius
            new Scalar(0, 0, 255),  //Scalar object for color
            10                     //Thickness of the circle
    );

    return mrgba;
}

in case

<org.opencv.android.JavaCameraView
    android:id="@+id/camera_view"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
/>

or even better get width and height from onCameraViewStarted() params:

@Override
public void onCameraViewStarted(int width, int height) {
    mWidth = width;
    mHeight = height;
}