JavaFX 3D: label positioning is wrong while rotating the camera around the Z-axis - javafx

Question

I am currently writing a program in JavaFX, which visualises a graph in 3D. The user should be able to translate and rotate it.
As the common rule for movement in 3D is, to move the camera instead of the whole graph, I followed this rule.
I created a StackPane, which contains two Panes (bottomPane and topPane). The bottomPane contains the SubScene, in which the graph is displayed and which uses a PerspectiveCamera. In the topPane I put a Group containing the Labels for specific nodes.
I did this setup to prevent labels being hidden by the graph, when their corresponding nodes are behind other nodes or edges.
To get the positioning of the labels right, I bind a function to the translateX/Y/Z properties of the camera, which updates the positions of the labels accordingly (rearrangeLabels()).
This function calculates the screen coordinates of the nodes and then calculates these back to the coordinates of the group containing the labels.
This works perfectly for translation (e.g. moving the graph up/down/left/right). It also works, if I rotate the camera only around the x-axis OR the y-axis.
But when I want to rotate in both axis the same time (e.g. diagonal) the labels are not moving accordingly.
I tried a lot of different approaches and came to the conclusion, that this might be a bug in JavaFX, or more precise in either the localToScreen() or screenToLocal() function.
I attached a demo program, which depicts the mentioned problem.
Just press Start and use your primary mouse button to rotate the camera.
So my question is, does anyone of you know, if this is a known bug? And if yes, is there a workaround? Or am I doing something wrong?
EDIT: I narrowed the error down to being the rotation around the Z-axis. When rotating ONLY around the z-axis, the weird behaviour happens, whereas rotating around either the X-axis or the Y-axis alone, everything moves as expected.
import javafx.application.Application;
import javafx.geometry.Point2D;
import javafx.geometry.Point3D;
import javafx.scene.*;
import javafx.scene.control.Button;
import javafx.scene.control.Label;
import javafx.scene.layout.Pane;
import javafx.scene.layout.StackPane;
import javafx.scene.paint.Color;
import javafx.scene.shape.Cylinder;
import javafx.scene.shape.Sphere;
import javafx.scene.transform.Rotate;
import javafx.scene.transform.Transform;
import javafx.scene.transform.Translate;
import javafx.stage.Stage;
public class RotateCamWithLabel extends Application{
Sphere node1;
Sphere node2;
Cylinder edge;
Label nodeLabel1;
Label nodeLabel2;
Group labelGroup;
Group graphGroup;
Pane topPane;
Pane bottomPane;
PerspectiveCamera cam;
double oldPosX;
double oldPosY;
Transform camTransform = new Rotate();
#Override
public void start(Stage primaryStage) throws Exception {
// Setting up the root of the whole Scene
topPane = new Pane();
topPane.setPickOnBounds(false);
bottomPane = new Pane();
StackPane root = new StackPane();
root.getChildren().addAll(bottomPane, topPane);
Button startButton = new Button("Start");
startButton.setOnAction(event -> {
setUpSubSceneAndCam();
addLabels();
});
topPane.getChildren().add(startButton);
// Starting the Scene
Scene scene = new Scene(root, 700, 500);
primaryStage.setScene(scene);
primaryStage.show();
}
private void setUpSubSceneAndCam() {
createGraph();
SubScene subScene = new SubScene(graphGroup, 700, 500, true, SceneAntialiasing.BALANCED);
subScene.setFill(Color.LIGHTGRAY);
cam = new PerspectiveCamera(true);
cam.setTranslateZ(-1000);
cam.setNearClip(0.1);
cam.setFarClip(Double.MAX_VALUE);
subScene.setCamera(cam);
bottomPane.getChildren().add(subScene);
createCameraLabelBinding();
subScene.setOnMousePressed(event -> {
oldPosX = event.getSceneX();
oldPosY = event.getSceneY();
});
subScene.setOnMouseDragged(event -> {
double deltaX = event.getSceneX() - oldPosX;
double deltaY = event.getSceneY() - oldPosY;
if (event.isPrimaryButtonDown()) {
rotateCamera(deltaX, deltaY);
}
oldPosX = event.getSceneX();
oldPosY = event.getSceneY();
});
}
// Rotation is done by calculating the local camera position in the subscene and out of these,
// the rotation axis is calculated as well as the degree.
// Then the camera is repositioned on the pivot point, turned based on the axis and degree, and put
// back along its local backwards vector based on the starting ditance between the camera and the pivot point
private void rotateCamera(double deltaX, double deltaY) {
// Calculate rotation-axis
Point3D leftVec = getCamLeftVector().multiply(deltaX);
Point3D upVec = getCamUpVector().multiply(deltaY);
Point3D dragVec = leftVec.add(upVec).multiply(-1);
Point3D backVec = getCamBackwardVector();
Point3D axis = dragVec.crossProduct(backVec);
//Point3D axis = Rotate.Z_AXIS; //Does not work
//Point3D axis = Rotate.Y_AXIS; //Works
//Point3D axis = Rotate.X_AXIS; //Works
Rotate r = new Rotate(dragVec.magnitude(), axis);
// set camera on pivot point
Point3D pivot = Point3D.ZERO;
Point3D camCurrent = new Point3D(cam.getTranslateX(), cam.getTranslateY(), cam.getTranslateZ());
Point3D camPivVec = pivot.subtract(camCurrent);
setCameraPosition(pivot);
// rotate camera
camTransform = r.createConcatenation(camTransform);
cam.getTransforms().setAll(camTransform);
// put camera back along the local backwards vector
double length = camPivVec.magnitude();
setCameraPosition(getCamBackwardVector().multiply(length).add(pivot));
}
private void addLabels() {
if (labelGroup != null) {
labelGroup.getChildren().remove(nodeLabel1);
labelGroup.getChildren().remove(nodeLabel2);
}
labelGroup = new Group();
topPane.getChildren().add(labelGroup);
nodeLabel1 = new Label("Hello");
nodeLabel2 = new Label("Bye");
labelGroup.getChildren().addAll(nodeLabel1, nodeLabel2);
rearrangeLabels();
}
private void createCameraLabelBinding() {
cam.translateXProperty().addListener((observable, oldValue, newValue) -> rearrangeLabels());
cam.translateYProperty().addListener((observable, oldValue, newValue) -> rearrangeLabels());
cam.translateZProperty().addListener((observable, oldValue, newValue) -> rearrangeLabels());
}
// TODO: Here is probably a bug
// I calculate the screen coordinates of the nodes, then turn them back to local positions
// in the label-group
private void rearrangeLabels() {
Point2D screenCoord1 = node1.localToScreen(Point2D.ZERO);
Point2D screenCoord2 = node2.localToScreen(Point2D.ZERO);
Point2D groupCoord1 = labelGroup.screenToLocal(screenCoord1);
Point2D groupCoord2 = labelGroup.screenToLocal(screenCoord2);
nodeLabel1.setTranslateX(groupCoord1.getX());
nodeLabel1.setTranslateY(groupCoord1.getY());
nodeLabel2.setTranslateX(groupCoord2.getX());
nodeLabel2.setTranslateY(groupCoord2.getY());
}
private void createGraph() {
graphGroup = new Group();
node1 = new Sphere(5);
node2 = new Sphere(5);
node1.setTranslateX(-50);
node1.setTranslateY(-50);
node2.setTranslateX(150);
node2.setTranslateY(50);
edge = new Cylinder(2, 10);
connectNodesWithEdge(new Point3D(node1.getTranslateX(), node1.getTranslateY(), node1.getTranslateZ()),
new Point3D(node2.getTranslateX(), node2.getTranslateY(), node2.getTranslateZ()));
graphGroup.getChildren().addAll(node1, node2, edge);
}
private void connectNodesWithEdge(Point3D origin, Point3D target) {
Point3D yAxis = new Point3D(0, 1, 0);
Point3D diff = target.subtract(origin);
double height = diff.magnitude();
Point3D mid = target.midpoint(origin);
Translate moveToMidpoint = new Translate(mid.getX(), mid.getY(), mid.getZ());
Point3D axisOfRotation = diff.crossProduct(yAxis);
double angle = Math.acos(diff.normalize().dotProduct(yAxis));
Rotate rotateAroundCenter = new Rotate(-Math.toDegrees(angle), axisOfRotation);
this.edge.setHeight(height);
edge.getTransforms().addAll(moveToMidpoint, rotateAroundCenter);
}
private Point3D getCamLeftVector() {
Point3D left = cam.localToScene(-1, 0, 0);
Point3D current = cam.localToScene(0, 0, 0);
return left.subtract(current);
}
private Point3D getCamUpVector() {
Point3D up = cam.localToScene(0, -1, 0);
Point3D current = cam.localToScene(0, 0, 0);
return up.subtract(current);
}
private Point3D getCamBackwardVector() {
Point3D backward = cam.localToScene(0, 0, -1);
Point3D current = cam.localToScene(0, 0, 0);
return backward.subtract(current);
}
private void setCameraPosition(Point3D position) {
cam.setTranslateX(position.getX());
cam.setTranslateY(position.getY());
cam.setTranslateZ(position.getZ());
}
public static void main(String[] args) {
launch(args);
}
}