I'm working on a couple audio plugins. Right now, they are audio units. And while the "DSP" code won't change for the most part between implementations / ports, I'm not sure how to go about the GUI.

For instance, I was looking at the Apple-supplied AUs in Lion. Does anyone know how did they go about the UI? Like, are the knobs and controls just subclasses of Cocoa controls? are they using some separate framework or coding these knobs and such from scratch?

And then, the plugs I'm working on are going to be available too as VSTs for Windows. I already have them up and running with generic interfaces. But I'm wondering if I should just get over it and recreate all my interfaces with the vstgui code provided by Steinberg or if there's a more practical approach to making the interfaces cross-platform.