Today I implemented a few new plugin functions to allow centered resizing in Xojo windows:
So if you resize the window, the center of the window will stay on the same place. It's difficult to show here in the blog, but maybe you simply try the project soon.
If you want to try soon, email me for a copy. Else wait for a new plugin prerelease.
PS: Works also in Real Studio if you still use that. Requires Cocoa target.