Cross posting from this post on the Technical Support & Bugs forum for development aspects…
The combinations that bdgza refers to turn out to be Accessibility controls, and in fact Control is an option for these as well. These potential OS-level (ie screen) zooming controls should be avoided by Vassal or any app, and include a set of keyboard variations:
Control, Command or Option (Alt) as a modifier on the Scroll action.
Key combinations: Alt+Command+8, Alt+Command±, Alt+Command+=
From my searches, I don’t think MacOS has or needs a keyboard modifier for scroll-wheel for zoom. I don’t have a mouse (yet) but from what I read I think it has the functionality to allow for zoom in and out. The trackpad certainly does, via the “pinch” and “separate” finger movements. However, I notice that only Apple applications seem to support that, of the ones I looked at.
I did a short survey of common Apple and cross-platform Apps to see what they do to control app-level zoom.
Keyboard-only control is the the common factor, using minus(-)/plus (+) keys for zoom out / in. Apple Maps & Google Maps also allow non-shifted/shifted variations; the most universal combination being Command= and Command-, if one had to choose just one set of keys that did not conflict with the Vassal feature whereby character keyboard presses passthrough to the chat window. At the same time, the editor’s ability to specify these keys in Zoom properties might need to be removed/deprecated (global option setting or enforced when the editor is used on old modules?). A potentially module impacting change but I would have thought standardisation of such a basic, generic function is worth it in the long term.
For mouse control, only Apple Maps does this but maybe that is a useful guide, considering what Vassal does.
The control is simply, Double-Click to zoom in and Option(Alt)-Double-Click to zoom out.
Apart from the choice of modifier on +/- keys, the above suggestions could apply to any vassal client.