JavaFX: How to make a ScrollPane pan only on middle button?

Question

JavaFX's ScrollPane panes on all mouse events when allowed to pan:

scrollPane.setPannable(true);  

How to limit the ScrollPane to pan only on middle mouse events, while still allowing all events to get to the StackPane's content?

Answer 1

You should consume all events except the middle button events inside the content's event handler:

// Let the ScrollPane.viewRect only pan on middle button.
imageLayer.addEventHandler(MouseEvent.ANY, event -> {
    if(event.getButton() != MouseButton.MIDDLE) event.consume();
});

This works because the ScrollPane pans via an event handler too, and event handlers are invoked bottom-up. Thus if we consume the event via the child, it won't get to the ScrollPane viewRect which does the panning.