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using System.Collections.Generic;
using Microsoft.Xna.Framework;
namespace V3.Map
{
// ReSharper disable once ClassNeverInstantiated.Global
public class Pathfinder
{
private const int CellHeight = Constants.CellHeight;
private const int CellWidth = Constants.CellWidth;
// An array of walkable search nodes
private SearchNode[,] mSearchNodes;
// The width of the map
private int mLevelWidth;
// the height of the map
private int mLevelHeight;
// List for nodes that are available to search
private readonly List<SearchNode> mOpenList = new List<SearchNode>();
// List for nodes that are NOT available to search
private readonly List<SearchNode> mClosedList = new List<SearchNode>();
//Calculates the distance between two (vector)points
private float Heuristic(Vector2 position, Vector2 goal)
{
return (goal - position).Length(); // Manhattan distance
}
public void LoadGrid(PathfindingGrid map)
{
mLevelWidth = map.mGridWidth;
mLevelHeight = map.mGridHeight;
InitializeSearchNodes(map);
}
private void InitializeSearchNodes(PathfindingGrid map)
{
mSearchNodes = new SearchNode[mLevelWidth, mLevelHeight];
// Creates a searchnode for each tile
for (int x = 0; x < mLevelWidth; x++)
{
for (int y = 0; y < mLevelHeight; y++)
{
SearchNode node = new SearchNode();
node.mPosition = new Vector2(x, y);
// Walk only on walkable tiles
node.mWalkable = map.GetIndex(x, y) == 0;
// Stores nodes that can be walked on
if (node.mWalkable)
{
node.mNeighbors = new SearchNode[4];
mSearchNodes[x, y] = node;
}
}
}
for (int x = 0; x < mLevelWidth; x++)
{
for (int y = 0; y < mLevelHeight; y++)
{
SearchNode node = mSearchNodes[x, y];
// Note only walkable nodes
if (node == null || node.mWalkable == false)
continue;
// The neighbors for every node
Vector2[] neighbors =
{
new Vector2(x, y - 1), // Node above the current
new Vector2(x, y + 1), // Node below the current
new Vector2(x - 1, y), // Node to the left
new Vector2(x + 1, y) // Node to the right
};
for (int i = 0; i < neighbors.Length; i++)
{
Vector2 position = neighbors[i];
// Test whether this neighbor is part of the map
if (position.X < 0 || position.X > mLevelWidth - 1 || position.Y < 0 ||
position.Y > mLevelHeight - 1)
continue;
SearchNode neighbor = mSearchNodes[(int)position.X, (int)position.Y];
// Keep a reference to the nodes that can be walked on
if (neighbor == null || neighbor.mWalkable == false)
continue;
// A reference to the neighbor
node.mNeighbors[i] = neighbor;
}
}
}
}
// Reset the state of the search node
private void ResetSearchNodes()
{
mOpenList.Clear();
mClosedList.Clear();
for (int x = 0; x < mLevelWidth; x++)
{
for (int y = 0; y < mLevelHeight; y++)
{
SearchNode node = mSearchNodes[x, y];
if (node == null)
continue;
node.mInOpenList = false;
node.mInClosedList = false;
node.mDistanceTraveled = float.MaxValue;
node.mDistanceToGoal = float.MaxValue;
}
}
}
// Returns the node with the smallest distance
private SearchNode FindBestNode()
{
SearchNode currentTile = mOpenList[0];
float smallestDistanceToGoal = float.MaxValue;
// Find the closest node to the goal
for (int i = 0; i < mOpenList.Count; i++)
{
if (mOpenList[i].mDistanceToGoal < smallestDistanceToGoal)
{
currentTile = mOpenList[i];
smallestDistanceToGoal = currentTile.mDistanceToGoal;
}
}
return currentTile;
}
// Use parent field to trace a path from search node to start node
private List<Vector2> FindFinalPath(SearchNode startNode, SearchNode endNode)
{
int counter = 0;
if (startNode == endNode)
{
return new List<Vector2>();
}
mClosedList.Add(endNode);
SearchNode parentTile = endNode.mParent;
// Find the best path
while (parentTile != startNode)
{
mClosedList.Add(parentTile);
parentTile = parentTile.mParent;
}
// Path from position to goal (from tile to tile)
List<Vector2> betaPath = new List<Vector2>();
// Final path after RayCasting
List<Vector2> finalPath = new List<Vector2>();
// Reverse the path and transform into the map
for (int i = mClosedList.Count - 1; i >= 0; i--)
{
betaPath.Add(new Vector2(mClosedList[i].mPosition.X * CellWidth + 8, mClosedList[i].mPosition.Y * CellHeight + 8));
}
// Short the path via RayCasting
for (int i = 1; i < betaPath.Count;)
{
if (!RayCast(betaPath[counter], betaPath[i]))
{
finalPath.Add(betaPath[i - 1]);
counter = i - 1;
}
else
{
i++;
}
}
finalPath.Add(betaPath[betaPath.Count - 1]);
return finalPath;
}
//Test Points
private Vector2 CheckStartNode(Vector2 startNode)
{
var start = startNode;
var startXPos = startNode;
var startXNeg = startNode;
var startYPos = startNode;
var startYNeg = startNode;
// When sprite is blocked out of map, he returns to the edge of the map
if (startNode.X > mLevelWidth - 2)
startNode.X = mLevelWidth - 2;
if (startNode.X < 2)
startNode.X = 2;
if (startNode.Y < 4)
startNode.Y = 4;
if (startNode.Y > mLevelHeight - 2)
startNode.Y = mLevelHeight - 2;
// When sprite stays on a null-position, he goes to the nearest non null-position around that null-position
while (mSearchNodes[(int)start.X, (int)start.Y] == null)
{
if (startXPos.X < mLevelWidth)
startXPos.X++;
if (startXNeg.X > 0)
startXNeg.X--;
if (startYPos.Y < mLevelHeight)
startYPos.Y++;
if (startYNeg.Y > 0)
startYNeg.Y--;
if (mSearchNodes[(int)startXPos.X, (int)start.Y] != null)
{
start.X = startXPos.X;
return start;
}
if (mSearchNodes[(int)startXNeg.X, (int)start.Y] != null)
{
start.X = startXNeg.X;
return start;
}
if (mSearchNodes[(int)start.X, (int)startYPos.Y] != null)
{
start.Y = startYPos.Y;
return start;
}
if (mSearchNodes[(int)start.X, (int)startYNeg.Y] != null)
{
start.Y = startYNeg.Y;
return start;
}
}
return start;
}
private Vector2 CheckEndNode(Vector2 endNode)
{
var end = endNode;
var endXPos = endNode;
var endXNeg = endNode;
var endYPos = endNode;
var endYNeg = endNode;
// When goal is null-position, the goal will be the nearest non null-position around that null-position
while (mSearchNodes[(int) end.X, (int) end.Y] == null)
{
if(endXPos.X < mLevelWidth - 3)
endXPos.X++;
if(endXNeg.X > 0)
endXNeg.X--;
if(endYPos.Y < mLevelHeight - 3)
endYPos.Y++;
if(endYNeg.Y > 0)
endYNeg.Y--;
if (endXPos.X > mLevelWidth - 3)
break;
if (endXNeg.X < 0)
break;
if (endYPos.Y > mLevelHeight - 3)
break;
if (endYNeg.Y < 0)
break;
if (mSearchNodes[(int)endXPos.X, (int)end.Y] != null)
{
end.X = endXPos.X;
return end;
}
if (mSearchNodes[(int)endXNeg.X, (int)end.Y] != null)
{
end.X = endXNeg.X;
return end;
}
if (mSearchNodes[(int)end.X, (int)endYPos.Y] != null)
{
end.Y = endYPos.Y;
return end;
}
if (mSearchNodes[(int)end.X, (int)endYNeg.Y] != null)
{
end.Y = endYNeg.Y;
return end;
}
}
return end;
}
// Finds the best path
public List<Vector2> FindPath(Vector2 startPoint, Vector2 endPoint)
{
// Start to find path if startpoint and endpoint are different
if (startPoint == endPoint)
{
return new List<Vector2>();
}
// Sprite don't walk out of the map
if (endPoint.Y > mLevelHeight - 2 || endPoint.Y < 4 || endPoint.X > mLevelWidth - 2 || endPoint.X < 2)
{
return new List<Vector2>();
}
// Test nodes for their validity
startPoint = CheckStartNode(startPoint);
endPoint = CheckEndNode(endPoint);
/*
* Clear the open and closed lists.
* reset each's node F and G values
*/
ResetSearchNodes();
// Store references to the start and end nodes for convenience
SearchNode startNode = mSearchNodes[(int)startPoint.X, (int)startPoint.Y];
SearchNode endNode = mSearchNodes[(int)endPoint.X, (int)endPoint.Y];
/*
* 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
*/
if (startNode != null)
{
startNode.mInOpenList = true;
startNode.mDistanceToGoal = Heuristic(startPoint, endPoint);
startNode.mDistanceTraveled = 0;
mOpenList.Add(startNode);
}
/*
* While the OpenList is not empty:
*/
while (mOpenList.Count > 0)
{
// Loop the open list and find the node with the smallest F value
SearchNode currentNode = FindBestNode();
// If the open list ist empty or a node can't be found
if (currentNode == null)
break;
// If the active node ist the goal node, we will find and return the path
if (currentNode == endNode)
return FindFinalPath(startNode, endNode); // Trace our path back to the start
// Else, for each of the active node's neighbors
for (int i = 0; i < currentNode.mNeighbors.Length; i++)
{
SearchNode neighbor = currentNode.mNeighbors[i];
// Make sure that the neighbor can be walked on
if (neighbor == null || !neighbor.mWalkable)
continue;
// Calculate a new G Value for the neighbors node
float distanceTraveled = currentNode.mDistanceTraveled + 1;
// An estimate of t he distance from this node to the end node
float heuristic = Heuristic(neighbor.mPosition, endPoint);
if (!neighbor.mInOpenList && !neighbor.mInClosedList)
{
// Set the neighbors node G value to the G value
neighbor.mDistanceTraveled = distanceTraveled;
// Set the neighboring node's F value to the new G value + the estimated
// distance between the neighbouring node and goal node
neighbor.mDistanceToGoal = distanceTraveled + heuristic;
// The neighbouring node's mParent property to point at the active node
neighbor.mParent = currentNode;
// Add the neighboring node to the open list
neighbor.mInOpenList = true;
mOpenList.Add(neighbor);
}
// Else if the neighboring node is in open or closed list
else if (neighbor.mInOpenList || neighbor.mInClosedList)
{
if (neighbor.mDistanceTraveled > distanceTraveled)
{
neighbor.mDistanceTraveled = distanceTraveled;
neighbor.mDistanceToGoal = distanceTraveled + heuristic;
neighbor.mParent = currentNode;
}
}
}
// Remove active node from the open list and add to the closed list
mOpenList.Remove(currentNode);
currentNode.mInOpenList = true;
}
// No path could be found
return new List<Vector2>();
}
// Check whether an area is completely walkable in given rectangle
public bool AllWalkable(Rectangle rectangle)
{
for (int x = rectangle.X; x <= rectangle.X + rectangle.Width; x++)
{
for (int y = rectangle.Y; y <= rectangle.Y + rectangle.Height; y++)
{
if (mSearchNodes[x / 16, y / 16] == null)
return false;
}
}
return true;
}
//Raycasting
private bool RayCast(Vector2 start, Vector2 goal)
{
var direction = goal - start;
var currentPos = start;
direction.Normalize();
//direction = direction * 8;
while (Vector2.Distance(currentPos, goal) > 1f)
{
if (mSearchNodes[(int)currentPos.X / 16, (int)currentPos.Y / 16] == null)
return false;
currentPos += direction;
}
return true;
}
}
}
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