FurnitureSpriteController.cs

    public Sprite GetSpriteForFurniture(Furniture furn)
    {
        string spriteName = furn.GetSpriteName();

        if (furn.LinksToNeighbour == false)
        {
            return SpriteManager.current.GetSprite("Furniture", spriteName);
        }

        // Otherwise, the sprite name is more complicated.
        spriteName += "_";

        // Check for neighbours North, East, South, West, Northeast, Southeast, Southwest, Northwest
        int x = furn.Tile.X;
        int y = furn.Tile.Y;
        string suffix = string.Empty;

        suffix += GetSuffixForNeighbour(furn, x, y + 1, "N");
        suffix += GetSuffixForNeighbour(furn, x + 1, y, "E");
        suffix += GetSuffixForNeighbour(furn, x, y - 1, "S");
        suffix += GetSuffixForNeighbour(furn, x - 1, y, "W");

        // Now we check if we have the neighbours in the cardinal directions next to the respective diagonals
        // because pure diagonal checking would leave us with diagonal walls and stockpiles, which make no sense.
        suffix += GetSuffixForDiagonalNeighbour(suffix, "N", "E", furn, x + 1, y + 1);
        suffix += GetSuffixForDiagonalNeighbour(suffix, "S", "E", furn, x + 1, y - 1);
        suffix += GetSuffixForDiagonalNeighbour(suffix, "S", "W", furn, x - 1, y - 1);
        suffix += GetSuffixForDiagonalNeighbour(suffix, "N", "W", furn, x - 1, y + 1);

        // For example, if this object has all eight neighbours of
        // the same type, then the string will look like:
        //       Wall_NESWneseswnw
        return SpriteManager.current.GetSprite("Furniture", spriteName + suffix);
    }

    private string GetSuffixForDiagonalNeighbour(string suffix, string coord1, string coord2, Furniture furn, int x, int y)
    {
        if (suffix.Contains(coord1) && suffix.Contains(coord2))
        {
            return GetSuffixForNeighbour(furn, x, y, coord1.ToLower() + coord2.ToLower());
        }

        return string.Empty;
    }

    private string GetSuffixForNeighbour(Furniture furn, int x, int y, string suffix)
    {
         Tile t = world.GetTileAt(x, y);
         if (t != null && t.Furniture != null && t.Furniture.ObjectType == furn.ObjectType)
         {
             return suffix;
         }

        return string.Empty;
    }