Custom Abstract Planes! (Easy Interim Fog of War)

I use abstract planes in black to act as a fog of war for my campaigns, but it gets a bit tedious to cover complex shapes, like curves, after a while. I know actual fog of war is a HUGE undertaking that is unlikely to see the light of day. But what if we made the hacky solution just about bit easier?

What if we took a page from Microsoft Office and copied their custom shapes feature? You could have a brush, which takes you to a top-down view of the map. Wherever the user clicks on on the map, the tool makes a vertex there. Keep clicking, and more vertices appear, each one connected to the previous vertex, until you reconnect the vertex chain back to the first point. A solid face would then fill in the space between the vertices, and you could recolor it like any other abstract object!

This would be a MUCH simpler thing to implement than a true fog of war system, and it would make the program a lot more usable for l users who use the program live at a table.