Game map from Code

Question

It's a long one so you might want to get that cup of tea/coffee you've been holding off on ;)

I run a game called World of Arl, it's a turn based strategy game akin to Risk or Diplomacy. Each player has a set of cities, armies and whatnot. The question revolves around the display of these things. Currently the map is created using a background image with CSS positioning of team icons on top of that to represent cities. You can see how it looks here: WoA Map

The background image for the map is located here: Map background and created in Omnigraffle. It's not designed to draw maps but I'm hopelessly incompetent with photoshop and this works for my purposes just fine.

The problem comes that I want to perform such fun things as pathfinding and for that I need to have the map somehow stored in code. I have tried using PIL, I have looked at incorporating it with Blender, I tried going "old school" and creating tiles as from many older games and finally I tried to use SVG. I say this so you can see clearly that it's not through lack of trying that I have this problem ;)

I want to be able to store the map layout in code and both create an image from it and use it for things such as pathfinding. I'm using Python but I suspect that most answers will be generic. The cities other such things are stored already and easily drawn on, I want to store the layout of the landmass and features on the landmass.

As for pathfinding, each type of terrain has a movement cost and when the map is stored as just an image I can't access the terrain of a given area. In addition to pathfinding I wish to be able to know the terrain for various things related to the game, cities in mountains produce stone for example.

Is there a good way to do this and what terms should I have used in Google because the terms I tried all came up with unrelated stuff (mapping being something completely different most of the time).

Edit 2: Armies can be placed anywhere on the map as can cities, well, anywhere but in the water where they'd sink, drown and probably complain (in that order).

After chatting to somebody on MSN who made me go over the really minute details and who has a better understanding of the game (owing to the fact that he's played it) it's occurring to me that tiles are the way to go but not the way I had initially thought. I put the bitmap down as it is now but also have a data layer of tiles, each tile has a given terrain type and thus pathfinding and suchlike can be done on it yet at the same time I still render using Omnigraffle which works pretty well.

I will be making an editor for this as suggested by Adam Smith. I don't know that graphs will be relevant Xynth but I've not had a chance to look into them fully yet.

I really appreciate all those that answered my question, thanks.

Answer 1

I'd store a game map in code as a graph.

Each node would represent a country/city and each edge would represent adjacency. Once you have a map like that, I'm sure you can find many resources on AI (pathfinding, strategy, etc.) online.

If you want to be able to build an image of the map programattically, consider adding an (x, y) coordinate and an image for each node. That way you can display all of the images at the given coordinates to build up a map view.

Answer 2

IMO, the map should be rendered in the first place instead of being a bitmap. What you should be doing is to have separate objects each knowing its dimensions clearly such as a generic Area class and classes like City, Town etc derived from this class. Your objects should have all the information about their location, their terrain etc and should be rendered/painted etc. This way you will have exact knowledge of where everything lies.

Another option is to keep the bitmap as it is and keep this information in your objects as their data. By doing this the objects won't have a draw function but they will have precise information of their placement etc. This is sort of duplicating the data but if you want to go with the bitmap option, I can't think of any other way.

Answer 3

If you just want to do e.g. 2D hit-testing on the map, then storing it yourself is fine. There are a few possibilities for how you can store the information:

• A polygon per island
• Representing each island as union of a list rectangles (commonly used by windowing systems)
• Creating a special (maybe greyscale) bitmap of the map which uses a unique solid colour for each island
• Something more complex (perhaps whatever Omnigiraffe's internal representation is)

Answer 4

You're going to have to translate your map into an abstract representation of some kind. Either a grid (hex or square) or a graph as xynth suggests. That's the only way you're going to be able to apply things like pathfinding algorithms to it.

Answer 5

The key thing to realize here is that you don't have to use just one map. You can use two maps:

• The one you already have which is drawn on screen
• A hidden map which isn't drawn but which is used for path finding, collision detection etc.

The natural next question then is where does this second map come from? Easy, you create your own tool which can load your first map, and display it. Your tool will then let you draw boundaries around you islands and place markers at your cities. These markers and boundaries (simple polygons e.g.) are stored as your second map and is used in your code to do path finding etc.

In fact you can have your tool emit python code which creates the graphs and polygons so that you don't have to load any data yourself.

I am just basically telling you to make a level editor. It isn't very hard to do. You just need some buttons to click on to define what you are adding. e.g. if you are adding a polygon. Then you can just add each mouse coordinate to an array each time you click on your mouse if you have toggled your add polygon button. You can have another button for adding cities so that each time you click on the map you will record that coordinate for the city and possibly a corresponding name that you can provide in a text box.

Answer 6

Asuming the map is fixed (not created on the fly) its "correct" to use a bitmap as graphical representation - you want to make it as pretty as possible.

For any game related features such as pathfinding or whatever fancy stuff you want to add you should add adequate data structures, even if that means some data is redundant.

E.g. describe the boundaries of the isles as polygon splines (either manually or automatically created from the bitmap, thats up to you and how much effort you want to spend and is needed to get the functionality you want).

To sum it up: create data structures matching the problems you have to solve, the bitmap is fine for looks but avoid doing pathfining or other stuff on it.