Limiting mouse movement of a 3D object to a plane in JavaFX

Question

I am using JavaFX to move 3D cubes with the mouse. The cube should remain on a plane stretched on the x and z axes. My solution works quite well, however, if I move the cube too quickly with the mouse or when it encounters an object with a certain depth (y axis), it is assumed that the mouse moves along the y axis and the cube starts to jump forward or backward. Is there a way to limit the mouse to the xz plane? A more complicated solution would be to project the length y back onto the xz plane, but I had no idea. I looked at JavaFX Moving 3D Objects but could not adapt it to my case.

My code is:

    private volatile double relMousePosX;
    private volatile double relMousePosZ;

    public void enableDragMove(PaneBox paneBox) {
        Group paneBoxGroup = paneBox.get();

        paneBoxGroup.setOnMousePressed((MouseEvent me) -> {
            if(isSelected(paneBox) && MouseButton.PRIMARY.equals(me.getButton())) {
                relMousePosX = me.getX();
                relMousePosZ = me.getZ();
            }
        });

        paneBoxGroup.setOnMouseDragged((MouseEvent me) -> {
            if(paneBoxGroup.focusedProperty().get() && MouseButton.PRIMARY.equals(me.getButton())) {
                setDragInProgress(paneBox, true);
                System.out.println(me.getY()); // should stay small value, but jumps to higher values at times, creating the problem.
                paneBoxGroup.setCursor(Cursor.MOVE);
                paneBox.setTranslateX(paneBox.getTranslateX() + (me.getX() - relMousePosX));
                paneBox.setTranslateZ(paneBox.getTranslateZ() + (me.getZ() - relMousePosZ));
            }
        });

        paneBoxGroup.setOnMouseReleased((MouseEvent me) -> {
            if(paneBoxGroup.focusedProperty().get() && MouseButton.PRIMARY.equals(me.getButton())) {
                setDragInProgress(paneBox, false);
                paneBoxGroup.setCursor(Cursor.DEFAULT);
            }
        });
   }

Answer 1

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@Override 
public void start(Stage stage) {
    final PerspectiveCamera cam = new PerspectiveCamera();
    cam.setFieldOfView(20);
    cam.setFarClip(10000);
    cam.setNearClip(0.01);
    cam.getTransforms().addAll(new Rotate(60,Rotate.X_AXIS),new Translate(-200,-200,300));

    final Group root = new Group();

    final Box floor = new Box(500, 500, 1);
    floor.setTranslateX(200);
    floor.setTranslateY(200);
    floor.setTranslateZ(50);
    floor.setMaterial(new PhongMaterial(Color.YELLOW));
    root.getChildren().add(floor);

    final Box box = new Box(50, 50, 50);
    box.setMaterial(new PhongMaterial(Color.RED));
    root.getChildren().add(box);

    final Rectangle rectangle = new Rectangle(400, 400, Color.TRANSPARENT);
    rectangle.setMouseTransparent(true);
    rectangle.setDepthTest(DepthTest.DISABLE);
    root.getChildren().add(rectangle);

    // D&D starts
    box.setOnDragDetected((MouseEvent event)-> {
        box.setMouseTransparent(true);
        rectangle.setMouseTransparent(false);
        box.setCursor(Cursor.MOVE);
        box.startFullDrag();
    });

    // D&D ends
    box.setOnMouseReleased((MouseEvent event)-> {
        box.setMouseTransparent(false);
        rectangle.setMouseTransparent(true);
        box.setCursor(Cursor.DEFAULT);
    });

    // While D&D, only confined to the rectangle
    rectangle.setOnMouseDragOver((MouseDragEvent event)-> {
        Point3D coords = event.getPickResult().getIntersectedPoint();
        coords = rectangle.localToParent(coords);
        box.setTranslateX(coords.getX());
        box.setTranslateY(coords.getY());
        box.setTranslateZ(coords.getZ());
    });

    final Scene scene = new Scene(root, 800, 600, true);
    scene.setCamera(cam);

    stage.setScene(scene);
    stage.setTitle("JavaFX 3D Drag&Drop");
    stage.show();
}

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