Xara's plug-in interface is incomplete, resulting in the effect you describe (other apps. show a view of the entire bitmap). I hoped Xara Ltd would fix the problem for the release of X, but that didn't happen so the only option is to reverse engineer the plug-in creation software (Filter Factory, long since abandoned by Adobe and its author). I may yet do it, but adding features by this method is very time consuming and has no material reward.

Regards - Sean