dream-young-soul / astar

A 2D A Star (A*) pathfinding implementation in C# focused on ease of use

A 2D A* (A Star) algorithm for C#

The world is represented by a WorldGrid that is essentially a matrix of the C# short data type. A value of 0 indicates the cell is closed / blocked. Any other number indicates the cell is open and traversable. It is recommended to use 1 for open cells as numbers greater and less than 0 may be used to apply penalty or priority to movement through those nodes in the future.

The WorldGrid can be indexed via either:

1. The provided Position struct where a row represents the vertical axis and column the horizontal axis (Similar to indexing into a matrix P_rc).

2. The C# Point struct that operates like a cartesian co-ordinate system where X represents the horizontal axis and Y represents the vertical axis (P_xy).

Paths can be found using either Positions (matrix indexing) or Points (cartesian indexing).

Example usage

   var pathfinderOptions = new PathFinderOptions { 
      PunishChangeDirection = true,
      UseDiagonals = false, 
   };

   var tiles = new short[,] {
      { 1, 0, 1 },
      { 1, 0, 1 },
      { 1, 1, 1 },
   };

    var worldGrid = new WorldGrid(tiles);
    var pathfinder = new PathFinder(worldGrid, pathfinderOptions);
    
    // The following are equivalent:
    
    // matrix indexing
    Position[] path = pathfinder.FindPath(new Position(0, 0), new Position(0, 2));
    
    // point indexing
    Point[] path = pathfinder.FindPath(new Point(0, 0), new Point(2, 0));

Options

• Allowing / restricting diagonal movement
• A choice of heuristic (Manhattan, MaxDxDy, Euclidean, Diagonal shortcut)
• The option to punish direction changes.
• A search limit to short circuit the search

FAQ

q. why doesn't this algorithm always find the shortest path?

a. A* optimises speed over accuracy. Because the algorithm relies on a heuristic to determine the distances from start and finish, it won't necessarily produce the shortest path to the target.

Changes from 1.0.0 to 1.1.0

• Reimplemented the punish change direction to perform more consistently

Changes from 0.1.x to 1.0.0

• The world is now represented by a WorldGrid that uses shorts internally instead of bytes
• If no path is found, the algorithm now reports an empty array instead of null
• Moved out of the AStar.Core namespace into simply AStar
• Replaced former Point class with the new Position class that uses Row / Column instead of X / Y to avoid confusion with cartesian co-ordinates
• Implemented support for Point class indexing and pathing which represent a traditional cartesian co-ordinate system
• Changed path from List to Array and changed type from PathFinderNode to Position or Point
• Reversed the order of the returned path to start at the start node
• Rationalised and dropped buggy options (heavy diagonals)