The bulk of the game exists in the board manager class. It is responsible for tracking who's turn it is, location of the pieces, and if the king is in check. The latter data is stored as part of a 3D array. The first two dimensions are x and y positions of the board. The 3rd dimension has 2 layers. Piece type and piece color. The bottom left of the grid rests at (0,0,0). When the player clicks on the screen it sends a raycast towards the grid and returns the cooridnates of the collision. These values are divided by the size of each grid space then rounded down. The board manager then checks to see what piece is in that position and proceeds accordingly.

To define movement behaviour the CreateMarker method is called for each space that piece can move to. The method has 3 arguments. Relative X position, Relative Y position, and Type. The type has 3 states. 2 is the most common. This is used for any space a piece can move to, and take at. The others are primarly used for pawns. 0 is used for any space a piece can move to, but cannot take at. 1 is used for a space a piece can ONLY take at, but cannot normally move to.

Example Piece Definitions

public class King : Piece  {
	public override void Movement() {
		base.CreateMarker(0, 1, 2);
		base.CreateMarker(0, -1, 2);
		base.CreateMarker(1, 0, 2);
		base.CreateMarker(-1, 0, 2);
		base.CreateMarker(1, 1, 2);
		base.CreateMarker(1, -1, 2);
		base.CreateMarker(-1, 1, 2);
		base.CreateMarker(-1, -1, 2);
	}
}
public class Pawn : Piece {
	public override void Movement() {
		if(color == 0) {
			base.CreateMarker(0, 1, 0);
			base.CreateMarker(-1, 1, 1);
			base.CreateMarker(1, 1, 1);
		}
		//Snip//
	}
}

public class Rook : Piece {
	public override void Movement() {
		int i = 1;
		int stopped = 0;
		while (stopped==0) { //up
			base.CreateMarker(0, i, 2);
			//If next is out of bounds, or colliding with another piece
			if (y + i >= 9) or (GameObject.FindWithTag("Grid").GetComponent().boardState[x, y + i, 0] != 0)
				stopped = 1;
			i++;     
		}
		//Snip//
	}
}

public class Piece : MonoBehaviour
{
	//Snip//
	public void OnMouseDown()
	{
		//Snip//
	}

	//Snip//

	public void CreateMarker (int rx, int ry, int type)
	{
		if ((x + rx >= 0) && (x + rx <= 9) && (y + ry >= 0) && (y + ry <= 9)) //If not out of bounds
		{
			if (GameObject.FindWithTag("Grid").GetComponent().gameState - 2 == color)
			{  // Same color
				bool empty = false;
				if (GameObject.FindWithTag("Grid").GetComponent().boardState[x + rx, y + ry, 0] == 0)
					empty = true;
				bool opponent = false;
				if (GameObject.FindWithTag("Grid").GetComponent().boardState[x + rx, y + ry, 1] != color)
					opponent = true;

				//Move Only
				if ((type == 0) && (empty == true))
					InstantiateMarker(rx, ry, type);
				//Take Only
				if ((type == 1) && (empty == false) && (opponent == true))
					InstantiateMarker(rx, ry, type);
				//Move/Take
				if ((type == 2) && ((empty == true) || (opponent == true)))
					InstantiateMarker(rx, ry, type);
			}
			else // Different color
			{
				if ((GameObject.FindWithTag("Grid").GetComponent().boardState[x + rx, y + ry, 1] != color) && (GameObject.FindWithTag("Grid").GetComponent().boardState[x + rx, y + ry, 0] == 1) && (type > 0))
				{
					GameObject.FindWithTag("Grid").GetComponent().check = true;
				}
			}
		}
	}

	public void InstantiateMarker(int rx, int ry, int type)
	{
		//Snip//
	}
		
	public virtual void Movement ()
	{
		//Snip//
	}
}

public class Piece : MonoBehaviour {
	//Snip//
	const int MOVE = 0;
	const int TAKE = 1;
	const int MOVETAKE = 2;
	const int KING = 1; { get; private set; }

	void OnMouseDown() {
		//Snip//
	}
	//Snip//
	void CreateMarker (int relativeX, int relativeY, int type) {
		BoardManager boardManager = GameObject.FindWithTag("Grid").GetComponent();
		Vector2Int position = new Vector2Int(x + relativeX, y + relativeY);
		if (isInBounds(position)) {      
			if (boardManager.getActivePlayer() == color) {                
				if ((type == MOVE)     && (IsEmpty(position)))
					InstantiateMarkerMove(position);
				if ((type == TAKE)     && (!IsEmpty(position)) && (IsOpponent(position)))
					InstantiateMarkerTake(position);
				if ((type == MOVETAKE) && ((IsEmpty(position)) || (IsOpponent(position))))
					InstantiateMarkerTake(position);
			}
			else if ((type > MOVE) && (IsOpponent(position)) && (boardManager.GetPieceAt(position) == KING))
				boardManager.check = true;
		}
	}

	virtual void Movement () {
	}

	void InstantiateMarkerMove(Vector2Int position) {
		//Snip//
	}

	void InstantiateMarkerTake(Vector2Int position) {
		//Snip//
	}

	bool IsInBounds(Vector2Int position) {
		if ((position.x >= 0) && (position.x <= 9) && (position.y >= 0) && (position.y <= 9)); return true; else return false;
	}

	bool IsEmpty(Vector2Int position) {
		if (boardManager.GetPieceAt(position) == 0); return true; else return false;
	}

	bool IsOpponent(Vector2Int position) {
		if (boardManager.GetColorAt(position) != color); return true; else return false;
	}
}