drawline cant't display a game

private const float TILE_SIZE = 1.0f;
private const float TILE_OFFSET = 0.5f;

private int selectionX = -1;
private int selectionY = -1;

private void Update(){
	PapanCatur ();
	UpdateSelection ();
}

private void UpdateSelection ()
{
	if (!Camera.main)
		return;
	RaycastHit hit;
	if (Physics.Raycast (Camera.main.ScreenPointToRay (Input.mousePosition), out hit, 25.0f, LayerMask.GetMask ("ChekersPlane"))) {
		selectionX = (int)hit.point.x;
		selectionY = (int)hit.point.z;
	} else {
		selectionX = -1;
		selectionY = -1;
	}
}

private void PapanCatur(){
	
	Vector3 widthLine = Vector3.right * 8;
	Vector3 heightline = Vector3.forward * 8;
	for(int i = 0; i<=8; i++){
		//debug.drawline cant display in game unity
		Vector3 start = Vector3.forward * i;
		Debug.DrawLine (start, start + widthLine,Color.yellow,0.0f, true);
		for (int j = 0; j <= 8; j++) {
			start = Vector3.right * j;
			Debug.DrawLine (start, start + heightline,Color.yellow,0.0f,true);
		}
	}
	//draw the selection
	if (selectionX >= 0 && selectionY >= 0) {
		Debug.DrawLine (
			Vector3.forward * selectionY + Vector3.right * selectionX,
			Vector3.forward * (selectionY + 1) + Vector3.right * (selectionX + 1));
		
		Debug.DrawLine (
			Vector3.forward * (selectionY + 1 ) +Vector3.right * selectionX,
			Vector3.forward * selectionY + Vector3.right * (selectionX + 1));

	}
}

}

Debug.DrawLine is meant for viewing in the scene window for debugging not inside the game window as an art asset. To use lines the way you want in a game you should use the LineRenderer instead.

oke thx bro