JavaFX TabPane fails to render when inside ScrollPane and zoomed Group - javafx

Question

I need a bunch of widgets, including a TabPane, inside a scrollable and zoomable view, basically this:
ScrollPane[ Group[ widgets .. including TabPane ] ]
The ScrollPane is obviously needed for scrolling, and the Group holds all the widgets and supports zooming.
The initial problem with that approach is that the ScrollPane shows scroll bars based on the original size of the widgets, not based on the actual size.
In the screenshot, note how scrollbars are shown even though the tab pane is much smaller than the viewport, so no scrollbars are needed.
The web site https://pixelduke.wordpress.com/2012/09/16/zooming-inside-a-scrollpane explains how to solve that by adding another nested Group:
ScrollPane[ Group[ Group[ widgets .. including TabPane ] ] ]
The inner Group, as before, holds all the widgets and supports zooming.
The outer Group automatically gets the layout bounds of the zoomed
widgets in the inner group, allowing the ScrollPane to correctly configure the scroll bars.
.. but now the TabPane will fail to properly draw itself.
All you see is the red background of the TabPane:
The complete tab pane only shows up once it's somehow forced to refresh.
The example code toggles the 'side' property of the tab pane when you press 'SPACE'.
Now I have it all: Tab Pane draws OK, inner group can be zoomed, scroll bars appear as soon as the zoomed content no longer fits the viewport. But having to force the Tab Pane refresh is certainly a hack.
Is there a fault in my scene graph?
Is this a bug in the TabPane rendering?
The problem certainly seems limited to the TabPane. When I add other groups, rectangles, buttons, text nodes to the 'widgets' in the inner group, they all render fine. Only the TabPane refuses to show its tabs.
Tried this with both JDK 1.8.0_51 and 1.8.0_73, also tried on Windows, Linux and Mac OS X.
import javafx.application.Application;
import javafx.geometry.Side;
import javafx.scene.Group;
import javafx.scene.Scene;
import javafx.scene.control.ScrollPane;
import javafx.scene.control.Tab;
import javafx.scene.control.TabPane;
import javafx.scene.input.KeyCode;
import javafx.scene.input.KeyEvent;
import javafx.scene.layout.Pane;
import javafx.scene.layout.Region;
import javafx.scene.paint.Color;
import javafx.scene.shape.Rectangle;
import javafx.stage.Stage;
public class TabDemo extends Application
{
#Override
public void start(final Stage stage)
{
// TabPane with some tabs
final TabPane tabs = new TabPane();
tabs.setStyle("-fx-background-color: red;");
for (int i=0; i<3; ++i)
{
final Rectangle rect = new Rectangle(i*100, 100, 10+i*100, 20+i*80);
rect.setFill(Color.BLUE);
final Pane content = new Pane(rect);
final Tab tab = new Tab("Tab " + (i+1), content);
tab.setClosable(false);
tabs.getTabs().add(tab);
}
tabs.setMinSize(Region.USE_PREF_SIZE, Region.USE_PREF_SIZE);
tabs.setPrefSize(400, 300);
final Group widgets = new Group(tabs);
widgets.setScaleX(0.5);
widgets.setScaleY(0.5);
final Group scroll_content = new Group(widgets);
final ScrollPane scroll = new ScrollPane(scroll_content);
final Scene scene = new Scene(scroll);
stage.setTitle("Tab Demo");
stage.setScene(scene);
stage.show();
// Unfortunately, the setup of ScrollPane -> Group -> Group -> TabPane
// breaks the rendering of the TabPane.
// While the red background shows the area occupied by TabPane,
// the actual Tabs are missing..
System.out.println("See anything?");
scene.addEventFilter(KeyEvent.KEY_PRESSED, (KeyEvent event) ->
{
if (event.getCode() == KeyCode.SPACE)
{ // .. until 'side' or 'tabMinWidth' or .. are twiddled to force a refresh
tabs.setSide(Side.BOTTOM);
tabs.setSide(Side.TOP);
System.out.println("See it now?");
}
});
}
public static void main(String[] args)
{
launch(args);
}
}