I'm about to work on related code. Have you any code to share so I would not break what you've done so far / reinvent the wheel.

See also bug #18179 for another reason why reworking this is a good idea.

> By the way, about the code, an important function for removing
> a base properly is missing in my opinion.

I already have a separate patch 95% complete for factoring that out. I should finish it.

Here's where I've got to:

First, after some work, I've more or less changed my mind about having a single "owner" field + borders flag in the tile; see below for reasoning. I'm now thinking about separate per-tile "tile owner" and "base owner" fields (both pointing to players).

Add new base flags "ownable" and "capturable". Make the existing "border_sq", "vision_main_sq", and "vision_invis_sq" properties require "ownable" to be set.

An "ownable" base is one that (usually) has an owner.

• The initial owner is that of the unit who created it.
• Once created, by default, an "ownable" base doesn't change owner. (Such a base can end up un-owned if a player is killed/removed, but this is rare. It could also happen with scenario/editor.)
• An "ownable" base doesn't necessarily act as a border source (only if "border_sq" is set).

A "capturable" base is an "ownable" base that changes hands when occupied by a unit at war with the current owner.

• Can't have a mixture of capturable and ownable-but-not-capturable bases on the same tile, so that's an automatic "conflicts" when loading rulesets.

[Edited: I hadn't seen bug #14236. While we're in there, it probably wouldn't be hard to add another option that controls whether a base remains owned when it contains no units. Would need to think a bit about details e.g. allied stacks.]

A fortress would thus be "ownable", "capturable", and have "border_sq" set -- this should result in no change from current behaviour.

A buoy would be "ownable" but not "capturable", and have the vision fields set, by default. Consequences:

• It doesn't claim any borders (not even the tile it's on). This fixes most of the problems originally raised.
• It can't be captured. The only way to stop the owner seeing with it is to pillage it (which is cheap and easy, if the owner isn't defending it).
• In particular, my buoy can be inside someone else's borders and still provide vision to me.

The last point is more or less why I changed my mind about having a single owner; when documenting "ownable" it seemed unnecessarily dirty to say "this can't change owners (unless you build a city nearby)". I don't think having two owners changes the design much, in fact. (Obviously border claiming bases must have the two owner fields the same...) It also makes the necessary changes to the editor much cleaner, I think.

Something I've had in the back of my mind while designing this is a sort of capture-the-flag scenario -- this would use ownable capturable "flag" bases which have no particular effect (no border source, etc).

One thing I haven't quite worked out is whether capture-by-unit and capture-by-borders should both be controlled by the "capturable" flag, or whether they need separate options. (I'm assuming the former, for now.)

As far as client UI is concerned, I was thinking of an "ownable" base displaying a flag like a city does (when citybar is disabled), but having this be overridden by shields if there's a unit on the tile. This has the advantage of not requiring new graphics :)

I've got a mess of code changes but nothing that compiles yet, and I've been getting a bit bogged down in the border code. I'll probably wait for bug #16613 and patch #1864 to land before taking this up again.

Assuming everyone's happy, I'd like to get it in 2.3.0, which is why I'm working on it now (since it changes packet formats etc), but it probably shouldn't be a blocker.

Related question: An empty bases (not protected by units) could be captured by enemy units?

Something I've been thinking for a while, but been reminded about by a discussion on the forum:

Buoys provide vision to a specific nation, so it's necessary to somehow track who they belong to. This is currently implemented by re-using the border/ownership mechanism: the tile with the buoy on becomes part of the nation's territory (likely an isolated tile).

This implementation causes various gameplay issues:

• Nations at peace with the buoy owner can't move into the buoy square. This allows obstructive nations to block off arbitrary parts of the ocean or straits with lines of buoys (which are cheap to build).
• Buoys act as "sea bases" for the purpose of reducing unhappiness in representative governments; buoys can be built at will anywhere in the world, and sea units and transported land units can use that tile as a base from which to carry out an aggressive campaign without the usual penalties.
• Unless playing with foggedborders, all players can deduce the location of a nation's buoys as soon as they are built.

I assume these are all unintended consequences.

IMO it would be better if there were a separate way to track ownership for bases without creating borders.

I don't think this new ownership concept needs to be per-base -- it's OK for all bases on a tile to have to "belong" to the same nation, and change ownership en masse -- so this probably means a change to the per-tile structure (which probably rules out changing this in S2_2).

I also don't think it makes sense for a base to be inside one nation's borders but "belong" to another, so continuing with a single "owner" field should suffice; an additional per-tile flag "borders" stating whether "owner" claims borders or is merely deriving benefits from any bases will suffice, I think.

I haven't thought this through exhaustively, but some implementation thoughts:

• The definition of borders will be changed to treat tiles with a zero "borders" flag as unclaimed territory, regardless of who "owner" is (currently this is signalled by a null "owner");
• When borders recede (e.g., city destroyed), the owner field is not cleared.
  • So a buoy near a city that is destroyed continues to give benefits to that city's erstwhile owner.
  • This leaves some "dead" but client-visible information in tiles without bases (effectively, the last claimant of that tile). If that's undesirable, the borders code could instead carefully clear owners except on tiles with all relevant bases, with the same effect.
• Pillaging an owned base on unclaimed territory will not automatically be an act of war against the owner as far as diplomatic states are concerned; it's undefended and in international waters, thus fair game. (But of course, in the case of a buoy, they probably saw you coming, and are free to take exception to that.)
  • Slightly unsure about this, but I think something of the sort is necessary for balance. Perhaps it could at least be a diplomatic incident (excuse for war) like certain Diplomat/Spy actions.
• The client UI would need to distinguish base and tile ownership in the tile middle-click popup.

Comments? Objections?