fix(ai): creatures pathfind around concave obstacles instead of oscillating (#2461)
## Summary Creatures (pets following, monsters chasing, NPCs approaching) would **oscillate — "pace back and forth really fast"** at concave obstacles (reported at the Britain Inn L-desk: a pet at `(1493,1614,20)` never reaching its master at `(1494,1605,21)`) instead of routing around them. **Root cause** (the A* pathfinder itself was correct): all goal-seeking funnels through `MoveTo` and `WalkMobileRange` → `MoveTowardsOrAwayFrom`, which step greedily via `DoMove(dir, badStateOk:true)`. `DoMove` returns `true` even when the direct step was blocked and the creature merely **auto-turned and sidestepped** (`MoveResult.SuccessAutoTurn`), and the caller then set `Path = null`, discarding the `PathFollower`. So at a concave obstacle a non-progressing sidestep was mistaken for progress and the creature never committed to a route. (AOS pet-follow runs at `CurrentSpeed = 0.1`, hence the "really fast" shuffle.) ## What changed - **New centralized `BaseAI.ApproachTarget(target, run, range)` primitive.** A greedy step is committed only when it **fully succeeds (`MoveResult.Success`) and actually gets closer**; otherwise the creature commits to a **persistent `PathFollower`** that routes around the obstacle and is never discarded by a greedy step. The open-terrain fast path (one greedy step, no pathfinding) is preserved. `MoveTo`, `MoveTowardsOrAwayFrom`, and `MoveToWithCollisionAvoidance` all delegate to it — public signatures unchanged, so no AI-class call site changes. - **Best-distance give-up + idle.** A creature that cannot reach a **stationary** in-range goal stops shuffling and idles after `ApproachGiveUpTicks` (40) ticks without lowering its closest-ever distance; a **moving** goal (active chase) never gives up. It resumes the moment the goal moves. - **Pathfinder fix (required):** `BitmapAStarAlgorithm.IsBlockedByDynamic` now skips the dynamic mobile-block check **at the goal cell only** (`MoveImpl.Goal`). Previously A* returned `null` whenever the target mobile stood on the goal cell, so creatures could never pathfind *toward* another mobile — only toward empty ground. The follower stops within `range` short of it. Static/item blocking and all non-goal mobile blocking are unchanged. ## Tests New AI-loop integration tests in `ApproachTargetTests.cs` drive the real `BaseAI` primitives against live Britain Inn map statics: exact-repro pet follow, open-terrain (asserts zero pathfinding), `MoveTo` chase (static + walking-away target), route-around-a-dynamic-wall, and walled-off give-up-and-idle. - Pathfinding + AI subset: **52/52** pass. - Full `UOContent.Tests`: **301/301** pass. (Note: the test host lingers on shutdown — a pre-existing infra quirk unrelated to this change; all tests complete and pass.) - Full solution build: clean (0 warnings / 0 errors). ## Notes - Branched off `main`; independent of the in-flight step-cache work. - Out of scope (future work): proactive "SmartAI" look-ahead pathfinding so clever creatures plan a route before walking into the obstacle, rather than reacting after they hit it. ## Test Plan - [X] In-game: order a pet to `follow`/`come` across the Britain Inn L-desk; confirm it routes around and reaches you instead of pacing. - [X] Aggro a monster and kite it around a building/treeline; confirm it chases around obstacles. - [X] Confirm open-terrain following/chasing feels unchanged (no extra latency). - [X] Confirm a creature with a genuinely unreachable target idles rather than shuffling forever.
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Kamron Batman
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4 changed files with 460 additions and 65 deletions
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@ -35,6 +35,7 @@ public class PathfindingTestFixture : ICollectionFixture<PathfindingTestFixture>
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Timer.Init(0);
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RaceDefinitions.Configure();
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MovementImpl.Configure();
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PathFollower.Configure();
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World.Load();
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World.ExitSerializationThreads();
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DecayScheduler.Configure();
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283
Projects/UOContent.Tests/Tests/Mobiles/AI/ApproachTargetTests.cs
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283
Projects/UOContent.Tests/Tests/Mobiles/AI/ApproachTargetTests.cs
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@ -0,0 +1,283 @@
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using System.Collections.Generic;
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using Server.Engines.Pathing.Cache;
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using Server.Mobiles;
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using Xunit;
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namespace Server.Tests.Mobiles.AI;
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// AI movement tests drive the real BaseAI primitives against live map statics. The
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// pathfinder uses non-reentrant static buffers, so we share the pathfinding sequential
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// collection to avoid parallel interference.
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[Collection("Sequential Pathfinding Tests")]
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public class ApproachTargetTests
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{
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private sealed class FollowerStub : BaseCreature
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{
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// Serial ctor + DefaultMobileInit bypasses NPCSpeeds JSON (absent in tests).
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public FollowerStub(Serial serial) : base(serial) => Body = 0xC9;
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}
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private sealed class TargetStub : Mobile
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{
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public TargetStub() => Body = 0xC9;
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}
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private static (FollowerStub bc, BaseAI ai) NewFollower(Map map, Point3D loc)
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{
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var bc = new FollowerStub(World.NewMobile);
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bc.DefaultMobileInit();
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bc.MoveToWorld(loc, map);
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BaseAI ai = new AnimalAI(bc);
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ai.AITimer?.Stop(); // we drive movement manually; no background timer
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return (bc, ai);
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}
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// Drives the pet follow primitive once per tick; returns true once it reaches within
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// arriveDist tiles. Uses InRange (Chebyshev) to match the game's own range semantics —
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// a diagonal neighbor at Euclidean ~2.24 is "within 2" to the engine.
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private static bool DriveFollow(BaseAI ai, Mobile bc, Mobile target, int arriveDist, int maxTicks)
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{
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for (var i = 0; i < maxTicks; i++)
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{
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ai.NextMove = 0;
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ai.WalkMobileRange(target, 1, false, 1, 2);
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if (bc.InRange(target, arriveDist))
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{
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return true;
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}
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}
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return false;
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}
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private static ushort FirstImpassableItemId()
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{
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for (ushort id = 1; id < TileData.MaxItemValue; id++)
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{
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if (TileData.ItemTable[id].ImpassableSurface)
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{
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return id;
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}
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}
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return 0;
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}
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[Fact]
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public void OpenTerrain_ReachesTarget_WithoutPathfinding()
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{
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var map = Map.Maps[1];
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Assert.NotNull(map);
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map.GetAverageZ(1500, 1600, out _, out var z, out _);
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var (bc, ai) = NewFollower(map, new Point3D(1500, 1600, (sbyte)z));
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var target = new TargetStub();
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target.MoveToWorld(new Point3D(1495, 1600, (sbyte)z), map); // 5 tiles west, open
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StepCache.Instance.Clear();
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var buildsBefore = StepCache.Instance.GetStats().BuildsTotal;
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var arrived = DriveFollow(ai, bc, target, 2, 40);
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var buildsAfter = StepCache.Instance.GetStats().BuildsTotal;
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bc.Delete();
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target.Delete();
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Assert.True(arrived, "creature should reach an open-terrain target by stepping");
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Assert.Equal(buildsBefore, buildsAfter); // greedy fast path: no chunk builds
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}
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[Fact]
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public void BritainInnDesk_PetReachesMaster()
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{
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var map = Map.Maps[1];
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Assert.NotNull(map);
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// Exact in-game repro: pet south of the L-desk, master north of it.
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var (bc, ai) = NewFollower(map, new Point3D(1493, 1614, 20));
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var target = new TargetStub();
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target.MoveToWorld(new Point3D(1494, 1605, 21), map);
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StepCache.Instance.Clear();
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// 200 ticks is generous for the ~17-step detour at one step per tick.
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var arrived = DriveFollow(ai, bc, target, 2, 200);
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bc.Delete();
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target.Delete();
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Assert.True(arrived, "pet must navigate around the L-desk to reach the master");
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}
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[Fact]
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public void MoveTo_ReachesTargetAroundDesk()
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{
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var map = Map.Maps[1];
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Assert.NotNull(map);
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var (bc, ai) = NewFollower(map, new Point3D(1493, 1614, 20));
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var target = new TargetStub();
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target.MoveToWorld(new Point3D(1494, 1605, 21), map);
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StepCache.Instance.Clear();
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var arrived = false;
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for (var i = 0; i < 200; i++)
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{
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ai.NextMove = 0;
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ai.MoveTo(target, false, 1);
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if (bc.InRange(target, 1))
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{
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arrived = true;
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break;
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}
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}
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bc.Delete();
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target.Delete();
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Assert.True(arrived, "MoveTo chaser must reach the target around the desk");
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}
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[Fact]
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public void MoveTo_CatchesTargetWalkingAway_OpenTerrain()
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{
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var map = Map.Maps[1];
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Assert.NotNull(map);
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map.GetAverageZ(1500, 1600, out _, out var z, out _);
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var (bc, ai) = NewFollower(map, new Point3D(1500, 1600, (sbyte)z));
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var target = new TargetStub();
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target.MoveToWorld(new Point3D(1498, 1600, (sbyte)z), map);
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StepCache.Instance.Clear();
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var caught = false;
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for (var i = 0; i < 60; i++)
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{
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ai.NextMove = 0;
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ai.MoveTo(target, true, 1);
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// Target walks west every other tick for its first several steps, then stops,
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// so a same-speed chaser eventually closes the gap.
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if (i % 2 == 0 && i < 16 && target.X > 1490)
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{
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target.MoveToWorld(new Point3D(target.X - 1, target.Y, target.Z), map);
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}
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if (bc.InRange(target, 1))
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{
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caught = true;
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break;
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}
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}
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bc.Delete();
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target.Delete();
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Assert.True(caught, "chaser must catch a target that walks away then stops");
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}
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[Fact]
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public void UnreachableTarget_GivesUp_AndIdles()
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{
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var map = Map.Maps[1];
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Assert.NotNull(map);
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map.GetAverageZ(1500, 1601, out _, out var z, out _);
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var (bc, ai) = NewFollower(map, new Point3D(1500, 1601, (sbyte)z));
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var target = new TargetStub();
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target.MoveToWorld(new Point3D(1500, 1596, (sbyte)z), map);
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// Full impassable ring around the target cell -> no path to within range 1.
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var id = FirstImpassableItemId();
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Assert.NotEqual<ushort>(0, id);
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var ring = new List<Item>();
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for (var x = 1499; x <= 1501; x++)
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{
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for (var y = 1595; y <= 1597; y++)
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{
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if (x == 1500 && y == 1596)
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{
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continue; // leave the target's own cell
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}
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map.GetAverageZ(x, y, out _, out var rz, out _);
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ring.Add(new Item(World.NewItem)
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{
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ItemID = id, Map = map, Location = new Point3D(x, y, (sbyte)rz)
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});
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}
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}
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StepCache.Instance.Clear();
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// Run well past the stuck window so give-up engages.
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for (var i = 0; i < 120; i++)
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{
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ai.NextMove = 0;
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ai.MoveTo(target, false, 1);
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}
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// After giving up, the creature must idle (not oscillate) while the goal is still.
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var idleStart = bc.Location;
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var stayedIdle = true;
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for (var i = 0; i < 20; i++)
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{
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ai.NextMove = 0;
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ai.MoveTo(target, false, 1);
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if (bc.Location != idleStart)
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{
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stayedIdle = false;
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break;
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}
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}
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var reached = bc.InRange(target, 1);
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bc.Delete();
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target.Delete();
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foreach (var it in ring)
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{
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it.Delete();
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}
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Assert.False(reached, "walled-off target must not be reached");
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Assert.True(stayedIdle, "after giving up, the creature must idle, not shuffle");
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}
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[Fact]
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public void WallBetween_RoutesAround_ReachesTarget()
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{
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var map = Map.Maps[1];
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Assert.NotNull(map);
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map.GetAverageZ(1500, 1600, out _, out var z, out _);
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var (bc, ai) = NewFollower(map, new Point3D(1500, 1600, (sbyte)z));
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var target = new TargetStub();
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target.MoveToWorld(new Point3D(1500, 1595, (sbyte)z), map); // 5 tiles north
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// Impassable wall on Y=1598 from X=1497..1503: blocks the straight line; ends open.
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var id = FirstImpassableItemId();
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Assert.NotEqual<ushort>(0, id);
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var wall = new List<Item>();
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for (var x = 1497; x <= 1503; x++)
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{
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map.GetAverageZ(x, 1598, out _, out var wz, out _);
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wall.Add(new Item(World.NewItem)
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{
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ItemID = id, Map = map, Location = new Point3D(x, 1598, (sbyte)wz)
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});
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}
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StepCache.Instance.Clear();
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var arrived = DriveFollow(ai, bc, target, 2, 200);
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bc.Delete();
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target.Delete();
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foreach (var it in wall)
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{
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it.Delete();
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}
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Assert.True(arrived, "creature must route around the wall to reach the target");
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}
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}
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