Question

Very weird problem, I finally managed to distill it into a small piece of code which demonstrates the problem. I have a pane, which contains 1 group, that groups contains a group which contains some ellipses. The top group has a rotate transform applied to it. The ellipses are made draggable.

Try the below example, drag some ellipses downwards (outside the group’s bounds), you’ll see them disappearing. If you maximize the window, they appear again but you can’t drag them anymore, they don’t receive any events anymore.

Now for the really strange part, there are three ways I can make the problem go away:

1. don’t apply the transform
2. remove one ellipse (!?) (I experimented to get to this number, 11)
3. start ScenicView alongside and select the group containing the ellipses so you can see the bounds of the group

I’m at a total loss here, completely stupefied. Please, does anyone have any idea why this problem is occuring and how to solve it?

Code (JavaFX 2.2.3 and java 1.7.0_09 64bit Windows 7):

import javafx.application.Application;
import javafx.event.EventHandler;
import javafx.geometry.Point2D;
import javafx.scene.Group;
import javafx.scene.GroupBuilder;
import javafx.scene.Node;
import javafx.scene.Scene;
import javafx.scene.SceneBuilder;
import javafx.scene.input.MouseEvent;
import javafx.scene.layout.Pane;
import javafx.scene.shape.Ellipse;
import javafx.scene.shape.EllipseBuilder;
import javafx.scene.transform.Rotate;
import javafx.scene.transform.RotateBuilder;
import javafx.stage.Stage;

public class DragProblem extends Application {
public static void main(String[] args) {
    launch(args);
}

@Override
public void start(Stage primaryStage) {
    DrawingPane drawingPane = new DrawingPane();
    drawingPane.setStyle("-fx-background-color: darkgrey;");

    Scene scene = SceneBuilder.create().root(drawingPane).width(1280d).height(1024d).build();

    primaryStage.setScene(scene);
    primaryStage.show();
}

public class DrawingPane extends Pane {
    private Group transformedGroup;
    private Group splinePoints;

    public DrawingPane() {
        transformedGroup = GroupBuilder.create().id("transformedGroup").build();

        getChildren().add(transformedGroup);

        addPoints();
        makePointsDraggable();
    }

    public void addPoints() {
        double[] coords = new double[] {
                // comment any one the below x,y coordinates and the problem doesn't occur..
                239.28353881835938, 488.2192687988281,
                245.04466247558594, 505.30169677734375,
                258.56671142578125, 539.49462890625,
                267.2294006347656, 563.618408203125,
                282.89141845703125, 587.84033203125,
                309.6925048828125, 602.2174072265625,
                327.4945068359375, 616.4683227539062,
                345.25445556640625, 633.718994140625,
                371.0416259765625, 649.0819702148438,
                393.78704833984375, 667.402587890625,
                442.67010498046875, 676.0886840820312 };

        splinePoints = GroupBuilder.create().build();
        for (int i = 0; i < coords.length; i += 2) {
            Ellipse ellipse = EllipseBuilder.create().radiusX(3).radiusY(3).centerX(coords[i]).centerY(coords[i + 1]).build();
            splinePoints.getChildren().add(ellipse);
        }

        transformedGroup.getChildren().add(splinePoints);

        Rotate rotateTransform = RotateBuilder.create().build();
        rotateTransform.setPivotX(224);
        rotateTransform.setPivotY(437);
        rotateTransform.setAngle(15);

        // ..or comment this line to prevent the problem occuring
        transformedGroup.getTransforms().add(rotateTransform);
    }

    public void makePointsDraggable() {
        for (final Node n : splinePoints.getChildren()) {
            Ellipse e = (Ellipse) n;
            final NodeDragHandler ellipseDragHandler = new NodeDragHandler(e, transformedGroup);

            e.setOnMousePressed(ellipseDragHandler);
            e.setOnMouseDragged(ellipseDragHandler);
        }
    }
}

public class NodeDragHandler implements EventHandler<MouseEvent> {
    protected final Ellipse node;
    private final Node transformedGroup;

    private double initialX;
    private double initialY;
    private Point2D initial;
    private boolean dragStarted = false;

    public NodeDragHandler(Ellipse node, Group transformedGroup) {
        this.node = node;
        this.transformedGroup = transformedGroup;
    }

    @Override
    public void handle(MouseEvent event) {
        if (!dragStarted) {
            initialX = event.getScreenX();
            initialY = event.getScreenY();

            initial = transformedGroup.localToParent(new Point2D(node.getCenterX(), node.getCenterY()));

            dragStarted = true;
        } else {
            double xDragged = event.getScreenX() - initialX;
            double yDragged = event.getScreenY() - initialY;

            Point2D newPos = new Point2D(initial.getX() + xDragged, initial.getY() + yDragged);

            Point2D p = transformedGroup.parentToLocal(newPos.getX(), newPos.getY());

            node.setCenterX(p.getX());
            node.setCenterY(p.getY());
        }
    }
}
}

Answer 1

It’s been acknowledged as a bug in JavaFX and will be solved in 2.2.6, see here. I’ve tested it with the early access release and I can confirm it has been solved.