public void Start()
{
if (grid.Source == null || grid.Destination == null)
{
return;
}
totalVisited = 0;
IsActive = true;
openList = new BinaryHeap<double, GridCell>();
currentCell = grid.Source;
currentCell.State = GridCellState.Closed;
}
public override void Update(GameTime gameTime)
{
if (!IsActive)
{
return;
}
foreach (var currentAdjacentCell in grid.GetValidAdjacentCells(currentCell))
{
if (currentAdjacentCell.State != GridCellState.Open)
{
currentAdjacentCell.State = GridCellState.Open;
currentAdjacentCell.Parent = currentCell;
currentAdjacentCell.H = Heuristic.GetEstimate(currentAdjacentCell.Position, grid.Destination.Position) * 10;
currentAdjacentCell.H += GetTieBreaker(currentAdjacentCell);
//currentAdjacentCell.H *= 1 + 1/1000f;
currentAdjacentCell.G = currentCell.G + (currentCell.IsOrthagonalWith(currentAdjacentCell) ? 10 : 14);
openList.Insert(currentAdjacentCell.F, currentAdjacentCell);
}
}
if (openList.Count == 0) //A path cannot be found
{
IsActive = false;
return;
}
totalVisited++;
currentCell = openList.RemoveMin();
currentCell.State = GridCellState.Closed;
if (grid.Destination.State == GridCellState.Closed) //A path has been found
{
var path = currentCell.GetPath();
IsActive = false;
PathFound(this, new PathFoundEventArgs(path, path.Count(),totalVisited -1));
}
base.Update(gameTime);
}
void SetCellType(GridCell cell, GridCellType type)
{
if (cell == null)
{
return;
}
cell.Type = type;
}
public bool IsOrthagonalWith(GridCell otherCell)
{
return Position.X == otherCell.Position.X || Position.Y == otherCell.Position.Y;
}
double GetTieBreaker(GridCell cell)
{
/*
* http://theory.stanford.edu/~amitp/GameProgramming/Heuristics.html#S12
*/
int dx1 = cell.Position.X - grid.Destination.Position.X,
dy1 = cell.Position.Y - grid.Destination.Position.Y,
dx2 = grid.Source.Position.X - grid.Destination.Position.X,
dy2 = grid.Source.Position.Y - grid.Destination.Position.Y,
cross = Math.Abs(dx1 * dy2 - dx2 * dy1);
return cross * 0.01;
}
