/// <summary>
/// Create a new instance of PathFinder
/// </summary>
/// <param name="searchParameters"></param>
public PathFinder(SearchParameters searchParameters)
{
this.searchParameters = searchParameters;
InitializeNodes(searchParameters.Map);
this.startNode = this.nodes[searchParameters.StartLocation.X, searchParameters.StartLocation.Y];
this.startNode.State = NodeState.Open;
this.endNode = this.nodes[searchParameters.EndLocation.X, searchParameters.EndLocation.Y];
}
/// <summary>
/// Returns any nodes that are adjacent to <paramref name="fromNode"/> and may be considered to form the next step in the path
/// </summary>
/// <param name="fromNode">The node from which to return the next possible nodes in the path</param>
/// <returns>A list of next possible nodes in the path</returns>
private List<Node> GetAdjacentWalkableNodes(Node fromNode)
{
List<Node> walkableNodes = new List<Node>();
IEnumerable<Point> nextLocations = GetAdjacentLocations(fromNode.Location);
foreach (var location in nextLocations)
{
int x = location.X;
int y = location.Y;
// Stay within the grid's boundaries
if (x < 0 || x >= this.width || y < 0 || y >= this.height)
continue;
Node node = this.nodes[x, y];
// Ignore non-walkable nodes
if (!node.IsWalkable)
continue;
// Ignore already-closed nodes
if (node.State == NodeState.Closed)
continue;
// Already-open nodes are only added to the list if their G-value is lower going via this route.
if (node.State == NodeState.Open)
{
float traversalCost = Node.GetTraversalCost(node.Location, node.ParentNode.Location);
float gTemp = fromNode.G + traversalCost;
if (gTemp < node.G)
{
node.ParentNode = fromNode;
walkableNodes.Add(node);
}
}
else
{
// If it's untested, set the parent and flag it as 'Open' for consideration
node.ParentNode = fromNode;
node.State = NodeState.Open;
walkableNodes.Add(node);
}
}
return walkableNodes;
}
/// <summary>
/// Attempts to find a path to the destination node using <paramref name="currentNode"/> as the starting location
/// </summary>
/// <param name="currentNode">The node from which to find a path</param>
/// <returns>True if a path to the destination has been found, otherwise false</returns>
private bool Search(Node currentNode)
{
// Set the current node to Closed since it cannot be traversed more than once
currentNode.State = NodeState.Closed;
List<Node> nextNodes = GetAdjacentWalkableNodes(currentNode);
// Sort by F-value so that the shortest possible routes are considered first
nextNodes.Sort((node1, node2) => node1.F.CompareTo(node2.F));
foreach (var nextNode in nextNodes)
{
// Check whether the end node has been reached
if (nextNode.Location == this.endNode.Location)
{
return true;
}
else
{
// If not, check the next set of nodes
if (Search(nextNode)) // Note: Recurses back into Search(Node)
return true;
}
}
// The method returns false if this path leads to be a dead end
return false;
}
