some more AStar improvements

CHANGELOG.md

@@ -20,8 +20,9 @@ Improvements
 - Improved EnumHelper.GetValues signature to return an array
 - Allow using external gesture handling alongside InputHandler through ExternalGestureHandling
 - Discard old data when updating a StaticSpriteBatch
-- **Drastically improved StaticSpriteBatch batching performance**
 - Multi-target net452, making MLEM compatible with MonoGame for consoles
+- Allow retrieving the cost of a calculated path when using AStar
+- **Drastically improved StaticSpriteBatch batching performance**
 
 Fixes
 - Fixed TokenizedString handling trailing spaces incorrectly in the last line of non-left aligned text

MLEM/Pathfinding/AStar.cs

@@ -78,7 +78,7 @@ namespace MLEM.Pathfinding {
             this.DefaultSpecialDirections = defaultSpecialDirections;
         }
 
-        /// <inheritdoc cref="FindPath"/>
+        /// <inheritdoc cref="FindPath(T,T,MLEM.Pathfinding.AStar{T}.GetCost,System.Nullable{float},System.Nullable{int},System.Nullable{bool},MLEM.Pathfinding.AStar{T}.GetSpecialDirections)"/>
         public Task<Stack<T>> FindPathAsync(T start, T goal, GetCost costFunction = null, float? defaultCost = null, int? maxTries = null, bool? allowDiagonals = null) {
             return Task.Run(() => this.FindPath(start, goal, costFunction, defaultCost, maxTries, allowDiagonals));
         }
@@ -95,8 +95,59 @@ namespace MLEM.Pathfinding {
         /// <param name="specialDirections">An optional function that determines a set of additional directions (or offsets) that should be tested for walkability.</param>
         /// <returns>A stack of path points, where the top item is the first point to go to, or null if no path was found.</returns>
         public Stack<T> FindPath(T start, T goal, GetCost costFunction = null, float? defaultCost = null, int? maxTries = null, bool? allowDiagonals = null, GetSpecialDirections specialDirections = null) {
-            var stopwatch = Stopwatch.StartNew();
+            this.TryFindPath(start, goal, out var path, out _, costFunction, defaultCost, maxTries, allowDiagonals, specialDirections);
+            return path;
+        }
 
+        /// <inheritdoc cref="FindPath(T,IEnumerable{T},MLEM.Pathfinding.AStar{T}.GetCost,System.Nullable{float},System.Nullable{int},System.Nullable{bool},MLEM.Pathfinding.AStar{T}.GetSpecialDirections)"/>
+        public Task<Stack<T>> FindPathAsync(T start, IEnumerable<T> goals, GetCost costFunction = null, float? defaultCost = null, int? maxTries = null, bool? allowDiagonals = null) {
+            return Task.Run(() => this.FindPath(start, goals, costFunction, defaultCost, maxTries, allowDiagonals));
+        }
+
+        /// <summary>
+        /// Tries to find paths between a <paramref name="start"/> position and a set of <paramref name="goals"/> and returns the path that had the lowest overall cost.
+        /// Note that this method is only faster than a one-to-many pathfinding method like Dijkstra's algorithm in situations where the amount of possible <paramref name="goals"/> is much lower than the total amount of possible positions, or the <paramref name="goals"/> are relatively close to each other.
+        /// </summary>
+        /// <param name="start">The point to start path finding at</param>
+        /// <param name="goals">The set of points to try to find a path to</param>
+        /// <param name="costFunction">The function that determines the cost for each path point</param>
+        /// <param name="defaultCost">The default cost for each path point</param>
+        /// <param name="maxTries">The maximum amount of tries before path finding is aborted</param>
+        /// <param name="allowDiagonals">If diagonals should be looked at for path finding</param>
+        /// <param name="specialDirections">An optional function that determines a set of additional directions (or offsets) that should be tested for walkability.</param>
+        /// <returns>A stack of path points, where the top item is the first point to go to, or null if no paths were found.</returns>
+        public Stack<T> FindPath(T start, IEnumerable<T> goals, GetCost costFunction = null, float? defaultCost = null, int? maxTries = null, bool? allowDiagonals = null, GetSpecialDirections specialDirections = null) {
+            var lowestCost = float.PositiveInfinity;
+            Stack<T> cheapestPath = null;
+            foreach (var goal in goals) {
+                if (!this.TryFindPath(start, goal, out var path, out var cost, costFunction, defaultCost, maxTries, allowDiagonals, specialDirections))
+                    continue;
+                if (cost < lowestCost) {
+                    lowestCost = cost;
+                    cheapestPath = path;
+                }
+            }
+            return cheapestPath;
+        }
+
+        /// <summary>
+        /// Tries to find a path between two points using this pathfinder's default settings or, alternatively, the supplied override settings.
+        /// </summary>
+        /// <param name="start">The point to start path finding at</param>
+        /// <param name="goal">The point to find a path to</param>
+        /// <param name="path">The path that was found, or <see langword="null"/> if no path was found.</param>
+        /// <param name="totalCost">The total cost that was calculated for the path, or <see cref="float.PositiveInfinity"/> if no path was found.</param>
+        /// <param name="costFunction">The function that determines the cost for each path point</param>
+        /// <param name="defaultCost">The default cost for each path point</param>
+        /// <param name="maxTries">The maximum amount of tries before path finding is aborted</param>
+        /// <param name="allowDiagonals">If diagonals should be looked at for path finding</param>
+        /// <param name="specialDirections">An optional function that determines a set of additional directions (or offsets) that should be tested for walkability.</param>
+        /// <returns>Whether a path was found.</returns>
+        public bool TryFindPath(T start, T goal, out Stack<T> path, out float totalCost, GetCost costFunction = null, float? defaultCost = null, int? maxTries = null, bool? allowDiagonals = null, GetSpecialDirections specialDirections = null) {
+            path = null;
+            totalCost = float.PositiveInfinity;
+
+            var stopwatch = Stopwatch.StartNew();
             var getCost = costFunction ?? this.DefaultCostFunction;
             var diags = allowDiagonals ?? this.DefaultAllowDiagonals;
             var tries = maxTries ?? this.DefaultMaxTries;
@@ -108,7 +159,6 @@ namespace MLEM.Pathfinding {
             open.Add(start, new PathPoint<T>(start, this.GetManhattanDistance(start, goal), null, 0, defCost));
 
             var count = 0;
-            Stack<T> ret = null;
             while (open.Count > 0) {
                 PathPoint<T> current = null;
                 foreach (var point in open.Values) {
@@ -122,7 +172,8 @@ namespace MLEM.Pathfinding {
                 closed.Add(current.Pos, current);
 
                 if (current.Pos.Equals(goal)) {
-                    ret = AStar<T>.CompilePath(current);
+                    path = AStar<T>.CompilePath(current);
+                    totalCost = current.F;
                     break;
                 }
 
@@ -141,7 +192,7 @@ namespace MLEM.Pathfinding {
             stopwatch.Stop();
             this.LastTriesNeeded = count;
             this.LastTimeNeeded = stopwatch.Elapsed;
-            return ret;
+            return path != null;
 
             void ExamineDirection(PathPoint<T> current, T dir) {
                 var neighborPos = this.AddPositions(current.Pos, dir);
@@ -192,7 +243,7 @@ namespace MLEM.Pathfinding {
         public delegate float GetCost(T currPos, T nextPos);
 
         /// <summary>
-        /// A delegate used by <see cref="AStar{T}.DefaultSpecialDirections"/> and <see cref="AStar{T}.FindPath"/> that determines a set of additional directions (or offsets) that should be tested for walkability.
+        /// A delegate used by <see cref="AStar{T}.DefaultSpecialDirections"/> and <see cref="AStar{T}.TryFindPath"/> that determines a set of additional directions (or offsets) that should be tested for walkability.
         /// </summary>
         /// <param name="currPos">The current position in the path.</param>
         /// <returns>A set of additional directions (or offsets) that should be checked for walkability. If the given <paramref name="currPos"/> has no special directions, an empty <see cref="IEnumerable{T}"/> should be returned.</returns>

Tests/PathfindingTests.cs

@@ -80,14 +80,42 @@ namespace Tests {
                 p => p.X == 2 && p.Y == 2 ? new[] {new Point(-1, 2)} : Enumerable.Empty<Point>()));
         }
 
+        [Test]
+        public void TestMultiplePaths() {
+            var area = new[] {
+                "XXXXXXXX",
+                "X  2  X",
+                "XXXXX X",
+                "X 53  X",
+                "X XXX X",
+                "X X X X",
+                "XXXXXXXX"
+            };
+            var pathfinder = PathfindingTests.CreatePathfinder(area, false);
+
+            var goals = new[] {new Point(1, 5), new Point(3, 5), new Point(5, 5)};
+            var goalCosts = new[] {19, float.PositiveInfinity, 9};
+            for (var i = 0; i < goals.Length; i++) {
+                pathfinder.TryFindPath(new Point(1, 1), goals[i], out _, out var cost);
+                Assert.AreEqual(goalCosts[i], cost);
+            }
+
+            var path = pathfinder.FindPath(new Point(1, 1), goals).ToArray();
+            var expected = new[] {new Point(1, 1), new Point(2, 1), new Point(3, 1), new Point(4, 1), new Point(5, 1), new Point(5, 2), new Point(5, 3), new Point(5, 4), new Point(5, 5)};
+            Assert.AreEqual(path, expected);
+        }
+
         private static Stack<Point> FindPathInArea(Point start, Point end, IEnumerable<string> area, bool allowDiagonals, AStar2.GetSpecialDirections getSpecialDirections = null) {
+            return PathfindingTests.CreatePathfinder(area, allowDiagonals, getSpecialDirections).FindPath(start, end);
+        }
+
+        private static AStar2 CreatePathfinder(IEnumerable<string> area, bool allowDiagonals, AStar2.GetSpecialDirections getSpecialDirections = null) {
             var costs = area.Select(s => s.Select(c => c switch {
                 ' ' => 1,
                 'X' => float.PositiveInfinity,
                 _ => (float) char.GetNumericValue(c)
             }).ToArray()).ToArray();
-            var pathFinder = new AStar2((_, p2) => costs[p2.Y][p2.X], allowDiagonals, 1, 64, getSpecialDirections);
+            return new AStar2((_, p2) => costs[p2.Y][p2.X], allowDiagonals, 1, 64, getSpecialDirections);
-            return pathFinder.FindPath(start, end);
         }
 
     }