The only way to do what you want is to use a rooted window in MacX. If you use
a rootless window, the client application will be completely responsible for
all scrolling, updating, and so on. At that point, the X Window System calls
are being mapped onto the Macintosh's Window Manager by MacX, and everything is
being handled remotely. This includes using the scroll bars, moving the
window, sizing the window, and so on.
If you use a rooted window instead, MacX will handle the bitmap, including the
updating and scrolling of images that are bigger than the Macintosh window they
are being displayed in.
In this case, the Macintosh window has nothing to do with the X Window System
Window Manager being used. Therefore, as long as the entire X Window System
image has been drawn in the Macintosh window's GrafPort, MacX will handle the
scrolling and upating locally.