JavaFX | changing Line anchor? - javafx

Question

I tried drawing a line and changing its end coordinate when dragging.
The problem is, it changes both of the lines' ends, with respect to the middle, supposedly the anchor.
Is there a way to move the anchor to the start of the line?
My code is:
Line path = new Line(30,30, 70 , 75);
path.setStrokeWidth(5);
Circle point = new Circle(3);
point.setCenterX(path.getEndX());
point.setCenterY(path.getEndY());
point.setFill(Paint.valueOf("red"));
point.setOnMouseDragged(e ->{
point.setCenterX(e.getX());
point.setCenterY(e.getY());
path.setEndX(point.getCenterX());
path.setEndY(point.getCenterY());
});
Group shapes = new Group();
shapes.getChildren().addAll(path, point);
BorderPane root = new BorderPane(shapes);
Scene scene = new Scene(root,600,400);
scene.getStylesheets().add(getClass().getResource("application.css").toExternalForm());
primaryStage.setScene(scene);
primaryStage.show();
the result:
The ideal is that the pivot point will be at the start of the line, and not at the middle.

Answer 1

What you're seeing is not the line growing or shrinking in both directions; instead, what's happening is, as the line changes length, the BorderPane repositions it in order to keep it centered. The same thing is happening with the "rotation". When you move an end in such a way as to change the angle of the line, the bounding box changes in a way that, when the BorderPane repositions the line, causes the other end to move in the opposite direction.
More specifically, the BorderPane is repositioning the Group—effectively the same thing since Group doesn't position its children. One fix for this is to make the Group unmanaged. This will stop the BorderPane from repositioning the Group as its bounds change. Note, however, that this will also stop the Group from contributing to the size and layout calculations of the BorderPane.
Here's an example:
import javafx.application.Application;
import javafx.geometry.Point2D;
import javafx.scene.Group;
import javafx.scene.Scene;
import javafx.scene.layout.BorderPane;
import javafx.scene.paint.Color;
import javafx.scene.shape.Circle;
import javafx.scene.shape.Line;
import javafx.stage.Stage;
public class Main extends Application {
private static void installDragHandlers(Circle circle) {
circle.setOnMousePressed(event -> {
Point2D offset = new Point2D(
event.getX() - circle.getCenterX(),
event.getY() - circle.getCenterY()
);
circle.setUserData(offset);
event.consume();
});
circle.setOnMouseDragged(event -> {
Point2D offset = (Point2D) circle.getUserData();
circle.setCenterX(event.getX() - offset.getX());
circle.setCenterY(event.getY() - offset.getY());
event.consume();
});
circle.setOnMouseReleased(event -> {
circle.setUserData(null);
event.consume();
});
}
#Override
public void start(Stage primaryStage) {
Line line = new Line(200, 200, 400, 200);
line.setStrokeWidth(2);
Circle start = new Circle(5, Color.GREEN);
start.centerXProperty().bindBidirectional(line.startXProperty());
start.centerYProperty().bindBidirectional(line.startYProperty());
installDragHandlers(start);
Circle end = new Circle(5, Color.RED);
end.centerXProperty().bindBidirectional(line.endXProperty());
end.centerYProperty().bindBidirectional(line.endYProperty());
installDragHandlers(end);
Group group = new Group(line, start, end);
group.setManaged(false);
primaryStage.setScene(new Scene(new BorderPane(group), 600, 400));
primaryStage.setTitle("SO-55196882");
primaryStage.show();
}
}
The Line is initialized with hard coded start and end points so that it is initially centered in the scene (whose initial dimensions are also hard coded).

Answer 2

Put shapes in group.
public void start(final Stage primaryStage) throws AWTException {
final Line path = new Line(30, 30, 70, 75);
path.setStrokeWidth(5);
final Circle point = new Circle(3);
point.setCenterX(path.getEndX());
point.setCenterY(path.getEndY());
point.setFill(Paint.valueOf("red"));
point.setOnMouseDragged(e -> {
point.setCenterX(e.getX());
point.setCenterY(e.getY());
path.setEndX(point.getCenterX());
path.setEndY(point.getCenterY());
});
final Group root = new Group(path, point);
primaryStage.setScene(new Scene(root));
primaryStage.show();
}