NetBeans VisualDebugger used to rely on the renderToImage(Object, float, boolean) method to obtain the scene's screenshot. This method has been removed as a result of implementing of RT-17398.

Unfortunately, it is not possible to use any of the remaining two forms of renderToImage() method because they require to be called on the FX application thread - the older versions were thread agnostic.

We will definitely need to address this in NetBeans but I want the problem to be tracked in JavaFX RT as well so we will get updates if anything changes in this particular API.
Also, the VisualDebugger used to pause all the JavaFX (scenegraph processing, animations, media etc.) - using com.sun.javafx.tk.Toolkit.pauseScenes() method - in order to grab the screenshot together with the scene metadata. Are there any planned changes in this area as well?

In NetBeans the problem is tracked as http://netbeans.org/bugzilla/show_bug.cgi?id=212945