Game positioning OO design

Question

Hi guyz,

I'm starting a game project, my first, it'll be like a civilization clone, with a big focus in war. I always worked with C# but for business apps (mostly web apps) so I have a doubt about what would be a good design to build the map positioning system.

I would like to each unit know where it's positioned, and to the map to know all units at each point, a two-way relationship, but I can't see what would be the best way to model this! I'd like some ideas and pseudo-code, if you could!

Thankz.

Answer 1

Make your map a two-dimensional array. At each position, put an array of all objects at that position. In addition, add position attributes to each object.

Yes, this will duplicate the information! So on each move you'll have to change the object and update the map.

However, fast reading and fast finding of the objects is very important for that kind of game. In addition, this solution avoids any search routine (e.g. go through the map and look for a particular object), which is generally a good idea: Replace all search routines over large datasets with indexes. The map should be seen as some kind of index over the object's position attributes.

Answer 2

The map should have all knowledge of all object on it. Furthermore, only each object on the map should know its location. This way, the map can ask all objects where they are and place them in their correct locations. You should never have to store the positioning information twice.

Answer 3

Here's one approach that should avoid duplication

Have a class which holds all objects on the map, and within it collections of different types of object

public class MapObjects
{
   private Collection<GamePiece> gamePieces;
}

Each item in the collections will hold its (current) map co-ordinates

public class GamePiece
{
   private MapCoordinate mapCoordinate;
   // Other items relevant to a GamePiece.. Health, ItemType, etc
}

To find where a particular selected item is on the map should be easy, you have a reference to the GamePiece which holds its coordinates. To find what items are in a particular coordinate you need a helper method, probably within the MapObjects class:

public class MapObjects
{
   public Collection<GamePiece> GamePiecesAtLocation(MapCoordinate mapCoordinate)
   {
      // Iterate through gamePieces collection and build a result 
      // collection of items at specified coordinates.
   }
}

Good luck, sounds like an interesting project with plenty of challenges.

Answer 4

I would make the map hexagonal instead of a grid, so you don't have the odd Civilization phenomenon where you can cover more ground diagonally. Beyond that, I would just have each unit store its own position, and when you need to know which units are in a particular hex just iterate through the whole collection. It's hard to imagine having so many units involved that this approach would be a performance problem.

Answer 5

NSPoint is extremely useful when it comes to things like this. Each gameobject should have it's own location. You could store these gameobjects in arrays, one for each player, one for the whole game, it's up to you.

I will warn you that this is a huge project, not only codewise, but content wise, and requires lots of back and forth work while balancing the game. You should really try a few smaller games before you go after this one. Nothing is stopping you from diving in, but you are going to hit a lot of walls and write some serious spaghetticode if your first game is something this large. I would suggest starting with something like checkers, to get the turn based side of things down.

This is all coming from the guy who is currently writing a roguelike as his first game project. In my defense it is relatively straightforward, but there are a lot of things I was not expecting, and something as simple as calculating the sight / fog of war taking obstructions into account uses complex algorithms. I don't regret picking a roguelike as my first game, but after seeing how complex even the most basic concepts can be to implement, something like a turn based strategy game is simply something I'll leave to the pros for now.

If you're currently having trouble thinking of a way to not only create the units, but represent the map and store the locations, what are you going to do when it comes time to code in research? cities? production? resource gathering? A random map generator? Trajectory calculation? Hit probability? Armor? Mobility? Line of sight? Random events? AI?

I'm not trying to crush your dreams by any means, it's just that the genre you picked is more complex than it seems. Your brain will overload and burst at the seams. (I could continue rhyming on topic, but I will refrain to remind you that you should really try something like checkers first.)

Answer 6

Good design = simple design.

Make the map a list of objects.

Object
    int X { get; set; }
    int Y { get; set; }

Map
    List<Object> objects
    Add(Object)
    Remove(Object)
    GetAt(X, Y)
    GetInBox(X,Y,Width,Height)
    GetInRadius(X,Y,Radius)

That should be all you need. If the Get(..) queries get too slow, add caching or divide the map into sectors and keep a list of objects for each sector and update it when they move. This helps dramatically if you have many static objects or objects that don't move too quickly from sector to sector. My guess is that in a turn-based game, you won't need to optimize at all.