Separation of game logic - extending game state to include location information?

Question

I'm currently making a conversion of a board game I have - I don't intend to release it, it's merely to sharpen up skills. I'm currently refactoring it to completely separate game logic from everything such as rendering, getting user input, etc. The game logic is now in a library independent of the project that is actually run.

However, I've come across the problem that, if I don't store piece positions in the game state (as the game logic does not need to know about these), I'm struggling to think of how to store this information in the project that deals with rendering/user input stuff, so that it may render pieces.

Game State

The game state looks like this within the game logic - each district used to have a Vector2 indicating where the trouble marker would be displayed, and each piece would also have a Vector2 indicating their position on the board. They do not at the moment, as I wish to only have such things in the game project, as opposed to the logic project

Environment
    City
        District
        District
            Trouble
            Piece(s)

I have thought of creating a clone of this structure but adding position information, or of trying to use inheritance. But both of these methods seem extremely painful to do in the situation, and I'd really prefer to keep the game logic completely unknowing of things like this.

How would I go about doing this cleanly? Is it possible, or do I need to do a complete rethink of things?

Answer 1

It depends on if the game logic needs to know what the physical position of a gamepiece is. If that is not the case you can separate the render logic entirely from the gamelogic.

Suppose the game is Monopoly. You need to consider how to represent the board based on the information. For it to render it only needs to know the type (station, street, chance), if there are gamepieces on the square, any houses or hotels. This is all gamedata.

There is no need to include the exact positions of all pieces as they are relative to their parent container. So calculate the number of houses on that tile and draw them relative to that tile. Alternatively a tile with houses in them could also be represented as a circle with dots on the edges where each dot represents a house. For this you also do not need to know any Vector2 information in the game logic, as the circles are based on the number of houses and relative to the position of the tile (which in turn is relative to the previous tile and so on). This way, the board could be represented as a circle or a long winding strip or exactly as the 'real' board. As the presentation is just a matter of how you plan to represent pieces on the gameboard.

It becomes a different story if your game is like a tabletop wargame, where real positions become key (for example, distances within a district influence the odds a gamepiece can 'hit' an other gamepiece. In that event, you will need an exact representation of the gameboard in your logic as well.