Rotating around two points in android not working

Question

I have two seperate (x, y) points that I want to use to apply rotation to a view.

The first point is fixed, and I find the values of it fairly easily (for example 200,200). My second point is where a TOUCH is present, so I grab the RawX and RawY points easily as well. I feed these two points into this method that I found on another stack overflow question.

private float findRotation(int firstPointX, int firstPointY, int secondPointX, int secondPointY) {  
           double delta_x = (firstPointX - secondPointX);
           double delta_y = (firstPointY - secondPointY);
           double radians = Math.atan2(delta_y, delta_x);       
           return (float) Math.toDegrees(radians);
       }

and I use the return of that to set the rotation of a View. Like so myView.setRotation(...). The result ends up being a crazy spinning view while I move the cursor/finger on the screen. Any ideas?

The two points I'm grabbing seem to be correct, leaving me guessing that maybe the findRotation method is incorrect.

My activity:

    public class MainActivity extends Activity {
    ImageView imageView;
    ImageView dragHandle;
    RelativeLayout layout;
    int rememberAngle;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        imageView = (ImageView) findViewById(R.id.imageView1);
        dragHandle = (ImageView) findViewById(R.id.imageView2);
        layout = (RelativeLayout) findViewById(R.id.relativeLayout2);

        resize(dragHandle);

    }


    public void resize(ImageView resizeButton) {
        resizeButton.setOnTouchListener(new View.OnTouchListener() {

            public boolean onTouch(View v, MotionEvent motionEvent) {

                if (motionEvent.getAction() == MotionEvent.ACTION_DOWN) {
                    int[] locationOfLayout = new int[2];
                    int[] locationOfDrag = new int[2];

                    layout.getLocationOnScreen(locationOfLayout);
                    dragHandle.getLocationOnScreen(locationOfDrag);

                    int firstPointX = locationOfLayout[0];
                    int firstPointY = locationOfLayout[1];

                    int secondPointX = dragHandle.getWidth() / 2 + locationOfDrag[0];
                    int secondPointY = dragHandle.getHeight() / 2 + locationOfDrag[1];


                    rememberAngle = (int) findRotation(firstPointX, firstPointY, secondPointX, secondPointY) + layout.getRotation();


                } else if (motionEvent.getAction() == MotionEvent.ACTION_MOVE) {
                    int[] locationOfLayout = new int[2];
                    int[] locationOfDrag = new int[2];

                    layout.getLocationOnScreen(locationOfLayout);
                    dragHandle.getLocationOnScreen(locationOfDrag);

                    int centerXOnLayout = layout.getWidth() / 2 + locationOfLayout[0];
                    int centerYOnLayout = layout.getHeight() / 2 + locationOfLayout[1];

                    int centerXOnDrag = dragHandle.getWidth() / 2 + locationOfDrag[0];
                    int centerYOnDrag = dragHandle.getHeight() / 2 + locationOfDrag[1];

                    layout.setRotation(findRotation(centerXOnLayout, centerYOnLayout, centerXOnDrag, centerYOnDrag) - rememberAngle);


                } else if (motionEvent.getAction() == MotionEvent.ACTION_UP) {

                }
                return true;
            }
        });
    }

    private float findRotation(int firstPointX, int firstPointY, int secondPointX, int secondPointY) {
        double delta_x = (secondPointX - firstPointX);
        double delta_y = (secondPointY - firstPointY);
        double radians = Math.atan2(delta_y, delta_x);
        return (float) Math.toDegrees(radians);
    }
}

My XML:

<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" >

    <RelativeLayout
        android:id="@+id/relativeLayout2"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_centerInParent="true" >

        <ImageView
            android:id="@+id/imageView1"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_centerHorizontal="true"
            android:layout_centerVertical="true"
            android:src="@drawable/ic_launcher" />

        <ImageView
            android:id="@+id/imageView2"
            android:layout_width="48dp"
            android:layout_height="48dp"
            android:layout_below="@+id/imageView1"
            android:layout_toRightOf="@+id/imageView1"
            android:src="@drawable/meanicons" />
    </RelativeLayout>

</RelativeLayout>

Answer 1

public void resize(ImageView resizeButton) {
    resizeButton.setOnTouchListener(new View.OnTouchListener() {

        float startAngle;
        float zeroAngle;
        int firstPointX;
        int firstPointY; 

        public boolean onTouch(View v, MotionEvent motionEvent) {

            if (motionEvent.getAction() == MotionEvent.ACTION_DOWN) {
                int[] locationOfLayout = new int[2];
                int[] locationOfDrag = new int[2];

                layout.getLocationOnScreen(locationOfLayout);
                dragHandle.getLocationOnScreen(locationOfDrag);

                firstPointX = locationOfLayout[0];
                firstPointY = locationOfLayout[1];

                int secondPointX = motionEvent.getRawX();
                int secondPointY = motionEvent.getRawY();

                zeroAngle = findRotation(firstPointX, firstPointY, secondPointX, secondPointY) // remember "zero" angle
                startAngle = layout.getRotation(); // remember angle at which layout is rotated at the start


            } else if (motionEvent.getAction() == MotionEvent.ACTION_MOVE) {

                layout.setRotation(findRotation(firstPointX, firstPointY, motionEvent.getRawX(), motionEvent.getRawY()) - zeroAngle + startAngle); // rotate relative to start and zero angle


            } else if (motionEvent.getAction() == MotionEvent.ACTION_UP) {

            }
            return true;
        }
    });
}

private float findRotation(int firstPointX, int firstPointY, int secondPointX, int secondPointY) {
    double delta_x = (secondPointX - firstPointX);
    double delta_y = (secondPointY - firstPointY);
    double radians = Math.atan2(delta_y, delta_x);
    return (float) Math.toDegrees(radians);
}