So based on the information from Java 2d rotation in direction mouse point
We need two things. We need the anchor point (which would be the centre point of the arc) and the target point, which would be the mouse point.
Using a MouseMotionListener
, its possible to monitor the mouse movements within the component
// Reference to the last known position of the mouse...
private Point mousePoint;
//....
addMouseMotionListener(new MouseAdapter() {
@Override
public void mouseMoved(MouseEvent e) {
mousePoint = e.getPoint();
repaint();
}
});
Next we need to calculate the angle between these two points...
if (mousePoint != null) {
// This represents the anchor point, in this case,
// the centre of the component...
int x = width / 2;
int y = height / 2;
// This is the difference between the anchor point
// and the mouse. Its important that this is done
// within the local coordinate space of the component,
// this means either the MouseMotionListener needs to
// be registered to the component itself (preferably)
// or the mouse coordinates need to be converted into
// local coordinate space
int deltaX = mousePoint.x - x;
int deltaY = mousePoint.y - y;
// Calculate the angle...
// This is our "0" or start angle..
rotation = -Math.atan2(deltaX, deltaY);
rotation = Math.toDegrees(rotation) + 180;
}
From here, you would need to subtract 90 degrees, which would give your arcs start angle and then use an extent of 180 degrees.