void IMapNeighbourMethod.Invoke(IMap map, ref MapCell source, ref MapCell neighbour, Directions direction)
{
if ((source.Walkability & (byte)direction) != (byte)direction)
{
return;
}
// If neighbor is diagonal to current, graph.Cost(current,neighbor)
// will return Sqrt(2). Otherwise it will return only the cost of
// the neighbor, which depends on its type, as set in the TileType enum.
// So if this is a normal floor tile (1) and it's neighbor is an
// adjacent (not diagonal) floor tile (1), newCost will be 2,
// or if the neighbor is diagonal, 1+Sqrt(2). And that will be the
// value assigned to costSoFar[neighbor] below.
int newCost = _costSoFar[_currentIndex] + map.Cost(_locomotion, _currentIndex, neighbour.Index);
// If there's no cost assigned to the neighbor yet, or if the new
// cost is lower than the assigned one, add newCost for this neighbor
if (!_costSoFar.ContainsKey(neighbour.Index) || newCost < _costSoFar[neighbour.Index])
{
// If we're replacing the previous cost, remove it
if (_costSoFar.ContainsKey(neighbour.Index))
{
_costSoFar.Remove(neighbour.Index);
_cameFrom.Remove(neighbour.Index);
}
_costSoFar.Add(neighbour.Index, newCost);
_cameFrom.Add(neighbour.Index, _currentIndex);
ref MapCell goal = ref map.GetCell(_goalIndex);
int priority = newCost + Heuristic(map, ref neighbour, ref goal);
if (!_pool.TryDequeue(out AStarPriorityQueueNode? neighbourNode))
{
neighbourNode = new AStarPriorityQueueNode {
CellIndex = neighbour.Index
};
}
else
{
neighbourNode !.CellIndex = neighbour.Index;
}
_frontier.Enqueue(neighbourNode, priority);
}
// Conduct the A* search
public Route GetPath(IMap map, ref MapCell start, ref MapCell goal, Locomotion locomotion)
{
_locomotion = locomotion;
if (!_pool.TryDequeue(out AStarPriorityQueueNode? startNode))
{
startNode = new AStarPriorityQueueNode {
CellIndex = start.Index
};
}
else
{
startNode !.CellIndex = start.Index;
}
// Add the starting location to the frontier with a priority of 0
_frontier.Enqueue(startNode, 0);
_cameFrom.Add(start.Index, start.Index); // is set to start, None in example
_costSoFar.Add(start.Index, 0);
while (_frontier.Count > 0)
{
// Get the Location from the frontier that has the lowest
// priority, then remove that Location from the frontier
AStarPriorityQueueNode current = _frontier.Dequeue();
// If we're at the goal Location, stop looking.
if (current.CellIndex == goal.Index)
{
break;
}
// Neighbors will return a List of valid tile Locations
// that are next to, diagonal to, above or below current
_currentIndex = current.CellIndex;
_goalIndex = goal.Index;
map.ForEachNeighbour(current.CellIndex, this);
_pool.Enqueue(current);
}
var path = new Route();
int step = goal.Index;
while (step != start.Index)
{
if (!_cameFrom.ContainsKey(step))
{
return(Empty);
}
path.Add(step);
step = _cameFrom[step];
}
// path.Add(start);
path.Reverse();
_frontier.Clear();
_costSoFar.Clear();
_cameFrom.Clear();
return(path);
}