/// <summary>
/// Calculate heuristics value (Manhattan distance)
/// </summary>
/// <param name="from">Start Node</param>
/// <param name="to">End Node</param>
/// <returns></returns>
private int Heuristic(AStarNode from, AStarNode to)
{
return Math.Abs(from.x - to.x) + Math.Abs(from.y - to.y);
}
/// <summary>
/// Calculates shortest path for a given grid
/// </summary>
/// <param name="grid">Grid with passable and not passable cells</param>
/// <param name="start">Starting node</param>
/// <param name="goal">Destination node</param>
/// <returns>Returns a list of nodes of the shortest path or null if can't find any</returns>
public List<AStarNode> AStarSearch(bool[,] grid, AStarNode start, AStarNode goal)
{
List<AStarNode> closedSet = new List<AStarNode>();
List<AStarNode> openSet = new List<AStarNode>();
openSet.Add(start);
List<AStarNode> comeFrom = new List<AStarNode>();
start.g = 0;
start.f = start.g + Heuristic(start, goal);
while (openSet.Count > 0)
{
AStarNode current = openSet.OrderBy(x => x.f).First();
if (current.x == goal.x && current.y == goal.y)
return Reconstruct(comeFrom, current);
openSet.Remove(current);
closedSet.Add(current);
// get all neighboring tiles
List<AStarNode> neighbors = new List<AStarNode>();
if (current.x > 0 && grid[current.x - 1, current.y])
neighbors.Add(new AStarNode(current.x - 1, current.y));
if (current.x < grid.GetLength(0) - 1 && grid[current.x + 1, current.y])
neighbors.Add(new AStarNode(current.x + 1, current.y));
if (current.y > 0 && grid[current.x, current.y - 1])
neighbors.Add(new AStarNode(current.x, current.y - 1));
if (current.y < grid.GetLength(1) - 1 && grid[current.x, current.y + 1])
neighbors.Add(new AStarNode(current.x, current.y + 1));
foreach (AStarNode neighbor in neighbors)
{
bool inClosedSet = false;
foreach (AStarNode test in closedSet)
if (test.x == neighbor.x && test.y == neighbor.y)
{
inClosedSet = true;
break;
}
if (inClosedSet)
continue;
int tentativeGScore = current.g + 1;
bool inOpenSet = false;
foreach (AStarNode test in openSet)
if (test.x == neighbor.x && test.y == neighbor.y)
{
inOpenSet = true;
break;
}
if (inOpenSet == false || tentativeGScore < neighbor.g)
{
neighbor.CameFromNode = current;
comeFrom.Add(neighbor);
neighbor.g = tentativeGScore;
neighbor.f = neighbor.g + Heuristic(neighbor, goal);
if (inOpenSet == false)
openSet.Add(neighbor);
}
}
}
return null;
}
/// <summary>
/// Reconstructs the path that was taken
/// </summary>
/// <param name="cameFrom">Parent node</param>
/// <param name="currentNode">Current node</param>
/// <returns>List of the path fragment</returns>
private List<AStarNode> Reconstruct(List<AStarNode> cameFrom, AStarNode currentNode)
{
if (cameFrom.Contains(currentNode))
{
List<AStarNode> p = Reconstruct(cameFrom, currentNode.CameFromNode);
p.Add(currentNode);
return p;
}
else
{
List<AStarNode> p = new List<AStarNode>();
p.Add(currentNode);
return p;
}
}