After much suffering i've got multiplayer somewhat working.

Here you can see two different perspectives on the world map. Note that a players routes are in solid black and the opponents are transparent.
Previous to this, the game itself has been theoretically multiplayer compatible. As it always runs with a server and client, and instead of using the network, actions are passed via a simple memory buffer.
So upgrading to real multiplayer still involved a lot of work around getting networking setup. Also there was a bunch of other tweaks and fixes and whole new menus that needed to be created so a player can even get into a game.
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