Stupid questions about keeping important calls on the FX application thread

Question

I'm working on a project that I've been developing for about the last 6 months. I'm using JavaFX as the graphical side, but I'm taking input from a music processing program called Max/MSP, and I'm getting user input from a camera. Both of these things need to run on separate threads from my FX application thread. Up until now, things have been going smoothly. I can manipulate things on screen from my user input, and I have two way communication working between my JavaFX application and Max. Now, however, I need to start actually drawing stuff at runtime. Up until now, pretty much all FX side manipulations of been to just make translations. I now need to create, add, and remove children from Nodes. So I'm of course getting an error saying "not on FX application thread". I understand why it isn't on this thread, and why this is a problem. So I made some changes, so that calls that will make changes to the nodes on the stage, will only note the data, and then make the changes later, on the FX application thread. And then I run into problems, involving my own stupidity...
I have no idea how to get these calls onto the FX application thread. I mean, this should be really easy. I'm obviously missing something. Or maybe I'm just really tired, and have been looking at this for too long, or maybe the fact that it's been 6 months since I wrote this part of the code. But I see my Mainstage class, which extends Application. It has a start function, which sets up all my on screen do-dads (extended from Nodes and such), calls stage.show()... and then seems to end. When I've done things like call translate functions on my nodes from my user input thread, or from my communication from Max thread, things seemed to have worked. But now I'm thinking I might have been handling that wrong from the ground up. It seems likely that I should be having a "main game loop" (it isn't actually a game, but still, same principle) where I can tell the stage to update all the various nodes with the changes that have happened since the last frame, and try to get everything to update in time for the graphics to render at a reliable frame rate. And yet, I'm just not seeing how to do that. I'm sure this should be obvious, but I'm flat out blanking. And the time crunch is starting to descend... Please, if you can point out some standard way of avoiding this hopefully common newb mistake, I would greatly appreciate it!
-cullam

Answer 1

Checkout the documentation on "Pulse" in the JavaFX Archictecture overview which may help clarify some of your questions.
http://docs.oracle.com/javafx/2.0/architecture/jfxpub-architecture.htm
In simple terms, as I understand it, the framework will check 60 times a second if anything is dirty and needs repainting. If everything is clean, it will do nothing. If something is dirty, it will repaint it (although the repaint is kind of clever and highly optimized to support region image caching, make use of hardware rendering, etc).
So you can see that the main rendering loop is essentially hidden from you. Instead you construct a SceneGraph, the system checks regularly whether or not the SceneGraph has changed, and if it has it renders the updated SceneGraph.
In most JavaFX applications, you have a UI with controls and add event handlers which respond to control input to update the SceneGraph. In such programs, creating a main loop is unnecessary.
You can set up an animation timeline say at, for example, 30fps (half the pulse rate), then, on every other pulse, nothing will have changed so no redraw will happen. This is only necessary if you are performing an animation or capturing camera input, etc yourself (rather than using a Transition for example).
Actually, if I get my state changes working properly in a runLater call, do I need to also write a main loop? No, you don't need to write a main loop. Depending on the exact application, you may want one, but if you are already getting events generated by your camera input at 30fps, processing each 30fps from the camera in a runLater call would work fine without creating a loop.
But you do need to be careful that you don't send too many runLater calls and eventually overload the JavaFX event queue. For example it makes no sense to make more than 60 runLater calls a second to update the scene, because the system will never update the scene more than 60 times a second anyway.
If you do get a working camera app integrated with JavaFX, please post or blog about it as I am sure many people are interested in such an application.