I am wondering if there is any functionality existing in VASSAL that I can exploit to create “overlays” for the maps on the map board. For example, if this is a military map, I want to be able to “overlay” unit boundaries and phase lines. I might want to overlay suspected enemy positions. Etc. Any ideas?

There is no in-built way where extra ‘map overlays’ as such can just be added.

I have always implemented ‘Overlays’ as you describe as At-Start stacks of standard, but very large counters containing the modified map image. The Overlay counter has a Layer trait containing the overlay image that can be turned on and off. The tricky bit is creating the Overlay the correct size and then getting it the At-Start stack in the correct place, but once done once, I have found this to be quite satisfactory.

Obviously, this can only be used for ‘pre-defined’ overlays that you create as part of the scenario.


I’ll mention that I have also done this “province-by-province” for the All Bridges Burning (COIN) module – each province has a large overlay piece with a Non-Rectangular trait so that it only accepts clicks “on the actual province”, and I made those pieces non-movable and turned off band-selecting for them (so you can band-select pieces in them without getting the province).

Thanks for the suggestions folks, but what I require is something much more dynamic. If you are familiar with kml/kmz files, that is close enough to what I need to be used as an example. I need to be able to load multiple kmz files as individual layers that I can turn on and off at will.


I recall reading that Vassal performance relating to game maps directly corrleates to pixel count, not file size. I have a 7500x6000 map which doesn’t presently have performance issues. What sort of impact would adding a dynamic at-start 7500x6000 overlay create? Is that going to divide map redraw performance in half? Does transparency reduce that performance load?

I did come up with a limited solution that fits my needs.

I place several game pieces in the exact center of the map board. I add one layer to each that is a transparent image the size of the whole map board. I set the pieces to never be selected, moved, etc. I then toggle the active state of the layers of the pieces. This gives me several toggleable overlays per module.

Furthermore, in my particular use case, I replace the images in the module every game turn and redistribute the new version of the module to the players.

I think you can do something like this with the built-in functionality of Vassal. At least theoretically - I have no idea about the actual performance or UI experience. Create a map with a blank transparent PNG image. Define all zones, regions, or hexes on that map even though the image is blank. Game pieces only interact with that top “layer”. Create multiple maps underneath that map for each keyhole markup. Again a PNG with a transparent background so you can see all layers below. For each keyhole map, check the box “Include toolbar button to show/hide”. I’ve never tried this, but it should work in theory…

Haha. I was typing my next response when we cross posted. Glad you figured it out…