Perhaps I should have been more specific: I am coding a VST plugin in which I want to write a GUI for my audio effect. Part of the process is overriding a method called
is platform-specific (HWND on windows; I-forget-what on Mac) (needless to say, this method is responsible for opening the plugin's GUI). For the time being, I am only interested in compiling my plugin on Windows, but I wanted to develop the application with cross-platform-ness in mind for the future. It seems unfortunate to me that the VST api is limiting in this way, but hey, who am I to complain (I agree with you that this seems like the wrong way of going about this).
wxWidgets has some platform-specific methods for reassigning an HWND to a wx::Frame, but that didn't seem to work to well when I tried it-- and I didn't try too hard because I prefer GTK if I can use it.