Prevent dragged circle from overlapping - javafx

Question

As mentioned in the title, i have two Circle 's the first is draggable and the second is fixed, I would rotate (with the drag) the first one around the second without overlapping them but my Circle reacts oddly, I'm sure the error comes from the drag condition but I don't know how to solve it, that's why I need your help, here is a minimal and testable code :
import javafx.application.Application;
import javafx.scene.Scene;
import javafx.scene.layout.Pane;
import javafx.scene.paint.Color;
import javafx.scene.shape.Circle;
import javafx.stage.Stage;
public class Collision extends Application{
private Pane root = new Pane();
private Scene scene;
private Circle CA = new Circle(20);
private Circle CB = new Circle(20);
private double xOffset = 0;
private double yOffset = 0;
#Override
public void start(Stage stage) throws Exception{
initCircles();
scene = new Scene(root,500,500);
stage.setScene(scene);
stage.show();
}
private void initCircles(){
CA.setCenterX(100);
CA.setCenterY(100);
CA.setFill(Color.rgb(255, 0, 0,0.2));
CA.setStroke(Color.BLACK);
CB.setCenterX(250);
CB.setCenterY(200);
CB.setFill(Color.rgb(255, 0, 0,0.2));
CB.setStroke(Color.BLACK);
CA.setOnMousePressed(evt->{
xOffset = CA.getCenterX() - evt.getSceneX();
yOffset = CA.getCenterY() - evt.getSceneY();
});
CA.setOnMouseDragged(evt->{
//get Scene coordinate from MouseEvent
drag(evt.getSceneX(),evt.getSceneY());
});
root.getChildren().addAll(CA,CB);
}
private void drag(double x, double y){
/* calculate the distance between
* the center of the first and the second circle
*/
double distance = Math.sqrt (Math.pow(CA.getCenterX() - CB.getCenterX(),2) + Math.pow(CA.getCenterY() - CB.getCenterY(),2));
if (!(distance < (CA.getRadius() + CB.getRadius()))){
CA.setCenterX(x + xOffset);
CA.setCenterY(y + yOffset);
}else{
/**************THE PROBLEM :Condition to drag************/
CA.setCenterX(CA.getCenterX() - (CB.getCenterX()-CA.getCenterX()));
CA.setCenterY(CA.getCenterY() - (CB.getCenterY()-CA.getCenterY()));
/*What condition must be established for the
* circle to behave correctly
*/
/********************************************************/
}
}
public static void main(String[] args) {
launch(args);
}
}
Here is a brief overview :
Note:
for my defense, i searched and found several subject close to mine but which have no precise or exact solution, among which:
-The circle remains blocked at the time of the collision
-Two circle that push each other
-JavaScript, Difficult to understand and convert to java
Thank you for your help !

Answer 1

Point2D can be interpreted as a 2D vector, and has useful methods for creating new vectors from it, etc. You can do:
private void drag(double x, double y){
// place drag wants to move circle to:
Point2D newCenter = new Point2D(x + xOffset, y+yOffset);
// center of fixed circle:
Point2D fixedCenter = new Point2D(CB.getCenterX(), CB.getCenterY());
// minimum distance between circles:
double minDistance = CA.getRadius() + CB.getRadius() ;
// if they overlap, adjust newCenter:
if (newCenter.distance(fixedCenter) < minDistance) {
// vector between fixedCenter and newCenter:
Point2D newDelta = newCenter.subtract(fixedCenter);
// adjust so that length of delta is distance between two centers:
Point2D adjustedDelta = newDelta.normalize().multiply(minDistance);
// move newCenter to match adjusted delta:
newCenter = fixedCenter.add(adjustedDelta);
}
CA.setCenterX(newCenter.getX());
CA.setCenterY(newCenter.getY());
}
Obviously, you could do all this without using Point2D and just doing the computation, but I think the API calls make the code easier to understand.