/// <summary>
/// Traverse neghbours and store a reference to it if possible.
/// </summary>
private void AddReferencesToNeighbours(Point[] neighbourPositions, SearchNode node)
{
for (int count = 0; count < neighbourPositions.Length; count++)
{
Point position = neighbourPositions[count];
// Check if the neighbour is part of the level.
if ((position.X >= 0 && position.X <= levelWidth - 1) &&
(position.Y >= 0 && position.Y <= levelHeight - 1))
{
SearchNode neighbour = searchNodes[position.X, position.Y];
// Add only walkable nodes.
if (neighbour != null && neighbour.Walkable)
{
// Store a reference to the neighbour.
node.Neighbours.Add(neighbour);
}
}
}
}
// <summary>
/// Splits our level up into a grid of nodes.
/// </summary>
private void InitializeSearchNodes(Map map)
{
searchNodes = new SearchNode[levelWidth, levelHeight];
//For each of the tiles in our map, we
// will create a search node for it.
for (int x = 0; x < levelWidth; x++)
{
for (int y = 0; y < levelHeight; y++)
{
//Create a search node to represent this tile.
SearchNode node = new SearchNode();
node.Position = new Point(x, y);
// Our enemies can only walk on grass tiles.
node.Walkable = map.GetIndex(x, y) == 0;
// We only want to store nodes
// that can be walked on.
if (node.Walkable == true)
{
node.Neighbors = new SearchNode[4];
searchNodes[x, y] = node;
}
}
}
// Now for each of the search nodes, we will
// connect it to each of its neighbours.
for (int x = 0; x < levelWidth; x++)
{
for (int y = 0; y < levelHeight; y++)
{
SearchNode node = searchNodes[x, y];
// We only want to look at the nodes that
// our enemies can walk on.
if (node == null || node.Walkable == false)
{
continue;
}
// An array of all of the possible neighbors this
// node could have. (We will ignore diagonals for now.)
Point[] neighbors = new Point[]
{
new Point (x, y - 1), // The node above the current node
new Point (x, y + 1), // The node below the current node.
new Point (x - 1, y), // The node left of the current node.
new Point (x + 1, y), // The node right of the current node
};
// We loop through each of the possible neighbors
for (int i = 0; i < neighbors.Length; i++)
{
Point position = neighbors[i];
// We need to make sure this neighbour is part of the level.
if (position.X < 0 || position.X > levelWidth - 1 ||
position.Y < 0 || position.Y > levelHeight - 1)
{
continue;
}
SearchNode neighbor = searchNodes[position.X, position.Y];
// We will only bother keeping a reference
// to the nodes that can be walked on.
if (neighbor == null || neighbor.Walkable == false)
{
continue;
}
// Store a reference to the neighbor.
node.Neighbors[i] = neighbor;
}
}
}
}
/// <summary>
/// Use the parent field of the search nodes to trace
/// a path from the end node to the start node.
/// </summary>
private List<Vector2> FindFinalPath(SearchNode startNode, SearchNode endNode)
{
closedList.Add(endNode);
SearchNode parentTile = endNode.Parent;
// Trace back through the nodes using the parent fields
// to find the best path.
while (parentTile != startNode)
{
closedList.Add(parentTile);
parentTile = parentTile.Parent;
}
List<Vector2> finalPath = new List<Vector2>();
// Reverse the path and transform into world space.
for (int i = closedList.Count - 1; i >= 0; i--)
{
finalPath.Add(new Vector2(closedList[i].Position.X * 32,
closedList[i].Position.Y * 32));
}
return finalPath;
}
private void ProcessNeighbours(SearchNode activeNode, List<SearchNode> openList)
{
foreach (var node in activeNode.Neighbours)
{
if (node.Walkable && !node.InClosedList)
{
if (!node.InOpenList)
{
// Add neighbours to open list if it isn't already there
openList.Add(node);
node.InOpenList = true;
// Mark active node as parent.
node.SetParent(activeNode);
// Set G value.
node.G = activeNode.G + 10;
}
else
{
int tempG = activeNode.G + 10; // 10 IF THERE IS NO DIAGONAL
if (node.G < 0 || node.G > tempG)
{
tempG = node.G;
// Mark active node as parent.
node.SetParent(activeNode);
}
}
}
}
}
/// <summary>
/// Use the parent field of the search nodes to trace
/// a path from the end node to the start node.
/// </summary>
private Stack<Vector2> FindFinalPath(SearchNode startNode, SearchNode endNode, List<SearchNode> closeList)
{
closeList.Add(endNode);
SearchNode parentTile = endNode.Parent;
var finalPath = new Stack<Vector2>();
// Trace back through the nodes using the parent fields
while (parentTile != startNode)
{
finalPath.Push(new Vector2(parentTile.Position.X * (int)Global.TileSize, parentTile.Position.Y * (int)Global.TileSize));
parentTile = parentTile.Parent;
}
// Reverse the path and transform into world space.
finalPath.Reverse();
return finalPath;
}
private SearchNode FindBestNode(List<SearchNode> openList)
{
SearchNode activeNode = new SearchNode();
// Finds next active node (minimal F value)
int minF = int.MaxValue;
foreach (var node in openList)
{
if (node.F < minF)
{
minF = node.F;
activeNode = node;
}
}
return activeNode;
}
/// <summary>
/// Creates node for each tile.
/// </summary>
private void CreateNodeForEachTile(Map map)
{
for (int coordX = 0; coordX < levelWidth; coordX++)
{
for (int coordY = 0; coordY < levelHeight; coordY++)
{
var node = new SearchNode();
node.Position = new Point(coordX, coordY);
// Mark walkable terrain. 0 represent path on map grid.
node.Walkable = map.GetValue(coordX, coordY) == WalkableLandValue;
// Store only walkable nodes.
if (node.Walkable)
{
node.Neighbours = new List<SearchNode>(); // TO BE CONSIDERED!!!
searchNodes[coordX, coordY] = node;
}
}
}
}
/// <summary>
/// Sets provided node as parent.
/// </summary>
public void SetParent(SearchNode parent)
{
this.Parent = parent;
this.F = this.G + this.H;
}
// <summary>
/// Splits our level up into a grid of nodes.
/// </summary>
private void InitializeSearchNodes(Map map)
{
searchNodes = new SearchNode[levelWidth, levelHeight];
//For each of the tiles in our map, we
// will create a search node for it.
for (int x = 0; x < levelWidth; x++)
{
for (int y = 0; y < levelHeight; y++)
{
//Create a search node to represent this tile.
SearchNode node = new SearchNode();
node.Position = new Point(x, y);
// Our enemies can only walk on grass tiles.
node.Walkable = map.GetIndex(x, y) == 0;
// We only want to store nodes
// that can be walked on.
if (node.Walkable == true)
{
node.Neighbors = new SearchNode[4];
searchNodes[x, y] = node;
}
}
}
// Now for each of the search nodes, we will
// connect it to each of its neighbours.
for (int x = 0; x < levelWidth; x++)
{
for (int y = 0; y < levelHeight; y++)
{
SearchNode node = searchNodes[x, y];
// We only want to look at the nodes that
// our enemies can walk on.
if (node == null || node.Walkable == false)
{
continue;
}
// An array of all of the possible neighbors this
// node could have. (We will ignore diagonals for now.)
Point[] neighbors = new Point[]
{
new Point(x, y - 1), // The node above the current node
new Point(x, y + 1), // The node below the current node.
new Point(x - 1, y), // The node left of the current node.
new Point(x + 1, y), // The node right of the current node
};
// We loop through each of the possible neighbors
for (int i = 0; i < neighbors.Length; i++)
{
Point position = neighbors[i];
// We need to make sure this neighbour is part of the level.
if (position.X < 0 || position.X > levelWidth - 1 ||
position.Y < 0 || position.Y > levelHeight - 1)
{
continue;
}
SearchNode neighbor = searchNodes[position.X, position.Y];
// We will only bother keeping a reference
// to the nodes that can be walked on.
if (neighbor == null || neighbor.Walkable == false)
{
continue;
}
// Store a reference to the neighbor.
node.Neighbors[i] = neighbor;
}
}
}
}
/// <summary>
/// Finds the optimal path from one point to another.
/// </summary>
public List <Vector2> FindPath(Point startPoint, Point endPoint)
{
// Only try to find a path if the start and end points are different.
if (startPoint == endPoint)
{
return(new List <Vector2>());
}
/////////////////////////////////////////////////////////////////////
// Step 1 : Clear the Open and Closed Lists and reset each node’s F
// and G values in case they are still set from the last
// time we tried to find a path.
/////////////////////////////////////////////////////////////////////
ResetSearchNodes();
// Store references to the start and end nodes for convenience.
SearchNode startNode = searchNodes[startPoint.X, startPoint.Y];
SearchNode endNode = searchNodes[endPoint.X, endPoint.Y];
/////////////////////////////////////////////////////////////////////
// Step 2 : Set the start node’s G value to 0 and its F value to the
// estimated distance between the start node and goal node
// (this is where our H function comes in) and add it to the
// Open List.
/////////////////////////////////////////////////////////////////////
startNode.InOpenList = true;
startNode.DistanceToGoal = Heuristic(startPoint, endPoint);
startNode.DistanceTraveled = 0;
openList.Add(startNode);
/////////////////////////////////////////////////////////////////////
// Setp 3 : While there are still nodes to look at in the Open list :
/////////////////////////////////////////////////////////////////////
while (openList.Count > 0)
{
/////////////////////////////////////////////////////////////////
// a) : Loop through the Open List and find the node that
// has the smallest F value.
/////////////////////////////////////////////////////////////////
SearchNode currentNode = FindBestNode();
/////////////////////////////////////////////////////////////////
// b) : If the Open List empty or no node can be found,
// no path can be found so the algorithm terminates.
/////////////////////////////////////////////////////////////////
if (currentNode == null)
{
break;
}
/////////////////////////////////////////////////////////////////
// c) : If the Active Node is the goal node, we will
// find and return the final path.
/////////////////////////////////////////////////////////////////
if (currentNode == endNode)
{
// Trace our path back to the start.
return(FindFinalPath(startNode, endNode));
}
/////////////////////////////////////////////////////////////////
// d) : Else, for each of the Active Node’s neighbours :
/////////////////////////////////////////////////////////////////
for (int i = 0; i < currentNode.Neighbors.Length; i++)
{
SearchNode neighbor = currentNode.Neighbors[i];
//////////////////////////////////////////////////
// i) : Make sure that the neighbouring node can
// be walked across.
//////////////////////////////////////////////////
if (neighbor == null || neighbor.Walkable == false)
{
continue;
}
//////////////////////////////////////////////////
// ii) Calculate a new G value for the neighbouring node.
//////////////////////////////////////////////////
float distanceTraveled = currentNode.DistanceTraveled + 1;
// An estimate of the distance from this node to the end node.
float heuristic = Heuristic(neighbor.Position, endPoint);
//////////////////////////////////////////////////
// iii) If the neighbouring node is not in either the Open
// List or the Closed List :
//////////////////////////////////////////////////
if (neighbor.InOpenList == false && neighbor.InClosedList == false)
{
// (1) Set the neighbouring node’s G value to the G value we just calculated.
neighbor.DistanceTraveled = distanceTraveled;
// (2) Set the neighbouring node’s F value to the new G value + the estimated
// distance between the neighbouring node and goal node.
neighbor.DistanceToGoal = distanceTraveled + heuristic;
// (3) Set the neighbouring node’s Parent property to point at the Active Node.
neighbor.Parent = currentNode;
// (4) Add the neighbouring node to the Open List.
neighbor.InOpenList = true;
openList.Add(neighbor);
}
//////////////////////////////////////////////////
// iv) Else if the neighbouring node is in either the Open
// List or the Closed List :
//////////////////////////////////////////////////
else if (neighbor.InOpenList || neighbor.InClosedList)
{
// (1) If our new G value is less than the neighbouring
// node’s G value, we basically do exactly the same
// steps as if the nodes are not in the Open and
// Closed Lists except we do not need to add this node
// the Open List again.
if (neighbor.DistanceTraveled > distanceTraveled)
{
neighbor.DistanceTraveled = distanceTraveled;
neighbor.DistanceToGoal = distanceTraveled + heuristic;
neighbor.Parent = currentNode;
}
}
}
/////////////////////////////////////////////////////////////////
// e) Remove the Active Node from the Open List and add it to the
// Closed List
/////////////////////////////////////////////////////////////////
openList.Remove(currentNode);
currentNode.InClosedList = true;
}
// No path could be found.
return(new List <Vector2>());
}
