fix: creatures track and chase targets reliably around corners (#2590)

### Summary

Fixes the long-standing reports of monsters losing track of players who run around a corner ("Is monster AI not using pathfinding? It seems to be LOS blocked by statics"). Root-cause investigation compared current behavior against RunUO line-by-line and traced the regressions through the AI overhaul era (#2232, #2246, #2379, #2401, #2461).

### Root causes and fixes

1. **Movement contract** — `MoveTo`/`ApproachTarget` returned false on every healthy mid-chase tick (true only on arrival), so MeleeAI's RunUO-inherited *"move failed and beyond RangePerception+1 → Guard"* clause — which RunUO only evaluated on genuine blockage — fired **every tick of every chase**. A mounted player trivially opens 17 tiles at a corner, the monster guards, Guard nulls the combatant, and re-acquisition is LOS-gated — unrecoverable through a wall. Movement now reports failure only on genuine failure (no step taken with no working path, or approach give-up). ArcherAI's equivalent clause moves to the hard leash.

2. **Last-known-position pursuit** — while a combatant is in LOS its position is recorded each think tick. When the target vanishes (corner, hiding, recall), the creature walks to the last-seen spot, stands guard there ~10s (restoring RunUO's guard grace, which had decayed to a single tick since #2246), and **re-engages instantly** if the same target re-enters view — bypassing the 10s reacquire throttle.

3. **`ChaseLeashRange`** — new virtual on BaseCreature (default `RangePerception * 2` = 32 tiles) replaces the inline `RangePerception * 3` (48) in Melee/Mage/Archer AI. Per-creature tunable via `[props`.

4. **Group movement demoted to a crowding refinement** — previously any uncontrolled creature with one ally within 8 tiles on the same target used greedy ring-stepping for the *entire* chase, with wall-slides counted as success, never invoking the pathfinder — the "aggroed but won't come around the corner" symptom for spawn groups. It now engages only near the target when allies actually contest the ring, and blocked/wall-slid steps escalate to the pathfinding approach primitive.

5. **Mages close distance on broken LOS** — a mage within casting range but LOS-blocked by geometry stood at the wall holding a spell target until the 60s combatant expiry (ProcessTarget short-circuits Think and its RunTo stands off at RangeFight). Geometry-blocked mages now close in until LOS returns, both pre-cast and while holding a target. Hidden targets (CanSee) and poison-cure priority unchanged. The new movement contract also stops the constant spurious `OnFailedMove` teleport rolls mid-chase.

6. **Move budget: one actual step per AI tick** — nothing advanced `NextMove` on a normal step (RunUO's `m_NextMove` budget was lost), so code paths attempting several moves in one think tick could cross multiple tiles at once — visible as "warping" when crowded creatures jockey for position. A successful step now consumes a half-step budget (floor 50ms): blocks intra-tick double moves, stays safely below the timer interval so legitimate next-tick moves are never jitter-throttled, and does not reintroduce `TransformMoveDelay` inflation. Blocked attempts consume nothing, so retry ladders (repath-and-step, the collision fan) are unaffected. `CanMoveNow` is also wraparound-safe now.

### Reference behavior

RunUO requires LOS to *acquire* a target and to *land* a hit or spell — never to *continue* a chase (its MeleeAI LOS bail-out is literally commented out in stock code). Chases drop only on: target hidden, target dead/off-map, beyond `RangePerception * 3`, 60s without combat interaction, or blocked movement while far away. This PR restores those semantics while adding the last-known-position investigation on top. NPC run flags are untouched — pace is AI-timer-driven and most NPC art has no run animation.
This commit is contained in:
Kamron Batman 2026-08-23 01:13:00 -07:00 committed by GitHub
parent 2935eafe24
commit 8e39da2810
No known key found for this signature in database
GPG key ID: B5690EEEBB952194
7 changed files with 277 additions and 38 deletions

View file

@ -47,7 +47,7 @@ public class ArcherAI : BaseAI
{
this.DebugSayFormatted($"I am still not in range of {combatant.Name}");
if ((int)Mobile.GetDistanceToSqrt(combatant) > Mobile.RangePerception + 1)
if (!Mobile.InRange(combatant, Mobile.ChaseLeashRange))
{
this.DebugSayFormatted($"I have lost {combatant.Name}");

View file

@ -36,10 +36,32 @@ public abstract partial class BaseAI
}
}
private bool UseGroupMovement(Mobile target) =>
/// <summary>
/// Crowding refinement for the final approach: engages only near the target when allies
/// contest the ring, so creatures spread instead of stacking. Chasing any real distance
/// always uses the pathfinding approach primitive.
/// </summary>
private bool UseGroupMovement(Mobile target, int range) =>
Mobile.Combatant == target
&& !Mobile.Controlled
&& CountNearbyAllies(target) > 0;
&& Mobile.InRange(target, range + 2)
&& CountCrowdingAllies(target, range) > 0;
private int CountCrowdingAllies(Mobile target, int range)
{
var crowding = 0;
foreach (var m in target.GetMobilesInRange(range + 1))
{
if (m != Mobile && m.Combatant == target && m is BaseCreature { Controlled: false } bc
&& bc.Team == Mobile.Team)
{
crowding++;
}
}
return crowding;
}
public static bool MoveToWithGroup(BaseAI ai, Mobile target, bool run, int range)
{
@ -56,6 +78,7 @@ public abstract partial class BaseAI
{
if (optimalPosition == Point3D.Zero)
{
return ai.MoveToWithCollisionAvoidance(target, run, range);
}
@ -68,7 +91,15 @@ public abstract partial class BaseAI
direction = GetAdjustedDirection(direction);
}
return ai.DoMove(direction, true);
var res = ai.DoMoveImpl(direction, true);
if (res is MoveResult.Success or MoveResult.BadState)
{
return true;
}
// A blocked or wall-slid step is not progress — route around the obstacle.
return ai.ApproachTarget(target, run, range);
}
finally
{
@ -76,21 +107,6 @@ public abstract partial class BaseAI
}
}
private int CountNearbyAllies(Mobile target)
{
var allies = 0;
foreach (var m in Mobile.GetMobilesInRange(8))
{
if (m != Mobile && m.Combatant == target && m is BaseCreature { Controlled: false } bc
&& bc.Team == Mobile.Team)
{
allies++;
}
}
return allies;
}
private PooledRefList<BaseCreature> GetNearbyAllies(Mobile target)
{
var allies = PooledRefList<BaseCreature>.Create();

View file

@ -13,6 +13,7 @@
* along with this program. If not, see <http://www.gnu.org/licenses/>. *
************************************************************************/
using System;
using System.Runtime.CompilerServices;
using Server.Collections;
using Server.Items;
@ -58,7 +59,15 @@ public abstract partial class BaseAI
public bool CanMoveNow(out double delay)
{
delay = 0.0;
return Core.TickCount >= NextMove;
return Core.TickCount - NextMove >= 0;
}
// Caps movement at one actual step per AI think tick; pacing itself is the timer's
// cadence. Half a step keeps the budget below the timer interval so a legitimate
// next-tick move is never jitter-throttled.
private void ConsumeMoveBudget()
{
NextMove = Core.TickCount + Math.Max(50, (int)(Mobile.CurrentSpeed * 500));
}
public virtual bool CheckMove() => !(Mobile.Deleted || Mobile.DisallowAllMoves);
@ -103,6 +112,8 @@ public abstract partial class BaseAI
Mobile.CurrentSpeed = Mobile.PassiveSpeed;
}
ConsumeMoveBudget();
return MoveResult.Success;
}
@ -151,6 +162,7 @@ public abstract partial class BaseAI
if (Mobile.Move(Mobile.Direction))
{
ConsumeMoveBudget();
return MoveResult.SuccessAutoTurn;
}
}
@ -341,31 +353,72 @@ public abstract partial class BaseAI
if (res == MoveResult.BadState)
{
return false; // not allowed to move this tick; not a stall
return true; // not allowed to move this tick (frozen/casting/throttled); not a failure
}
if (res == MoveResult.Success && Mobile.GetDistanceToSqrt(target) < distBefore)
{
ResetApproach();
return Mobile.InRange(target, range);
return true; // healthy en-route progress
}
// else: fall through; let the PathFollower route around the obstacle.
}
// PLANNING PATH: a persistent PathFollower, never discarded by a greedy step.
if (Path == null || Path.Goal != target)
{
Path = new PathFollower(Mobile, target) { Mover = DoMoveImpl };
}
// Sample move-eligibility BEFORE the attempt: a successful step consumes the move
// budget, which would mask stall accounting and the progress signal.
var couldMove = CanMoveNow(out _) && !IsInBadState();
var locBefore = Mobile.Location;
if (Path.Follow(run, range))
{
ResetApproach();
return true;
}
TrackApproachProgress(target);
return false;
TrackApproachProgress(target, couldMove);
// En-route progress is success; failure only when a move-eligible tick took no step
// (no working path), or the approach has given up.
var progressed = !_approachGaveUp && (Mobile.Location != locBefore || !couldMove);
return progressed;
}
/// <summary>
/// Walks toward a fixed point (e.g. a target's last-known position), pathfinding around
/// obstacles. Returns false on arrival or when genuinely unable to make progress.
/// </summary>
public bool MoveToPoint(IPoint3D goal, bool run)
{
if (Mobile.Deleted || Mobile.DisallowAllMoves || goal == null)
{
return false;
}
if (Path?.Goal != goal)
{
Path = new PathFollower(Mobile, goal) { Mover = DoMoveImpl };
}
var couldMove = CanMoveNow(out _) && !IsInBadState();
var locBefore = Mobile.Location;
if (Path.Follow(run, 1))
{
Path = null;
return false; // arrived
}
return Mobile.Location != locBefore || !couldMove;
}
/// <summary>
@ -376,11 +429,11 @@ public abstract partial class BaseAI
/// gives up and idles. A MOVING goal (an active chase) resets the baseline every tick,
/// so chases never give up even when the gap holds constant.
/// </summary>
private void TrackApproachProgress(Mobile target)
private void TrackApproachProgress(Mobile target, bool couldMove)
{
if (!CanMoveNow(out _))
if (!couldMove)
{
return; // a not-yet-due move (stun) is not a stall
return; // a tick that was never allowed to move (stun, stall) is not a stall
}
var dist = Mobile.GetDistanceToSqrt(target);
@ -408,6 +461,7 @@ public abstract partial class BaseAI
if (++_approachStallTicks >= ApproachGiveUpTicks)
{
_approachGaveUp = true;
_approachGaveUpGoalLoc = goalLoc;
Path = null;
@ -444,7 +498,7 @@ public abstract partial class BaseAI
return true;
}
if (UseGroupMovement(m))
if (UseGroupMovement(m, range))
{
return MoveToWithGroup(this, m, shouldRun, range);
}
@ -467,7 +521,11 @@ public abstract partial class BaseAI
var direction = Mobile.GetDirectionTo(target);
if (DoMove(direction, true))
// Wall-slide auto-turns must not count as progress, or a creature pinned on
// geometry reports success forever.
var res = DoMoveImpl(direction, true);
if (res is MoveResult.Success or MoveResult.BadState)
{
return true;
}
@ -476,14 +534,14 @@ public abstract partial class BaseAI
{
var clockwise = (Direction)(((int)direction + i) % 8);
if (DoMove(clockwise, true))
if (DoMoveImpl(clockwise, true) == MoveResult.Success)
{
return true;
}
var counterclockwise = (Direction)(((int)direction - i + 8) % 8);
if (DoMove(counterclockwise, true))
if (DoMoveImpl(counterclockwise, true) == MoveResult.Success)
{
return true;
}

View file

@ -26,11 +26,25 @@ namespace Server.Mobiles;
public abstract partial class BaseAI
{
// Last-known-position tracking: recorded while the combatant is in LOS; drives the
// guard-time investigation and the instant re-engage.
private const int GuardGraceDuration = 10_000;
private const int LkpFreshDuration = 30_000;
private const int InvestigateDuration = 15_000;
private ActionType _action;
public long _nextDetectHidden;
public DateTime _lastOrder = DateTime.MinValue;
public Mobile _commandIssuer;
private Mobile _lkpTarget;
private Point3D _lkpLocation;
private IPoint3D _lkpGoal; // boxed _lkpLocation handed to the PathFollower
private long _lkpExpireTick;
private long _guardStopTick;
private long _investigateStopTick;
private bool _investigating;
public PathFollower Path { get; protected set; }
public AITimer AITimer { get; }
public long NextMove { get; set; }
@ -233,6 +247,15 @@ public abstract partial class BaseAI
return true;
}
if (_action == ActionType.Combat)
{
UpdateLastKnownLocation();
}
else if (_action is ActionType.Wander or ActionType.Guard)
{
TryReengageLastKnown();
}
switch (Action)
{
case ActionType.Wander:
@ -323,6 +346,15 @@ public abstract partial class BaseAI
{
Mobile.Warmode = true;
Mobile.Combatant = null;
// Investigate a fresh last-seen position that is not already in view; the guard
// grace period begins once the investigation ends.
_investigating = _lkpTarget != null && Core.TickCount - _lkpExpireTick < 0 &&
!(Mobile.InRange(_lkpLocation, 1) ||
Mobile.InLOS(_lkpLocation) && Mobile.InRange(_lkpLocation, Mobile.RangePerception));
_investigateStopTick = Core.TickCount + InvestigateDuration;
_guardStopTick = Core.TickCount + GuardGraceDuration;
_lkpGoal = null;
}
private void HandleFleeAction()
@ -453,18 +485,118 @@ public abstract partial class BaseAI
public virtual bool DoActionGuard()
{
if (Mobile.Combatant == null)
if (_investigating)
{
DebugSay("No threats found. Going home...");
Action = ActionType.Wander;
if (InvestigateLastKnown())
{
return true;
}
_investigating = false;
_guardStopTick = Core.TickCount + GuardGraceDuration;
}
DebugSay("I stopped being on guard.");
if (Core.TickCount - _guardStopTick < 0)
{
DebugSay("I am on guard.");
if (Utility.Random(8) == 0)
{
Mobile.Direction = (Direction)Utility.Random(8);
}
return true;
}
DebugSay("I stopped being on guard. Going home...");
Action = ActionType.Wander;
return true;
}
/// <summary>
/// Records the combatant's position while it is visible and in line of sight.
/// </summary>
private void UpdateLastKnownLocation()
{
var combatant = Mobile.Combatant;
if (combatant?.Deleted == false && combatant.Map == Mobile.Map &&
Mobile.CanSee(combatant) && Mobile.InLOS(combatant))
{
_lkpTarget = combatant;
_lkpLocation = combatant.Location;
_lkpExpireTick = Core.TickCount + LkpFreshDuration;
}
}
/// <summary>
/// Re-engages the last-seen target when it returns to view within perception range,
/// bypassing the reacquire throttle.
/// </summary>
private bool TryReengageLastKnown()
{
var target = _lkpTarget;
if (target == null)
{
return false;
}
if (target.Deleted || !target.Alive || target.Map != Mobile.Map ||
target is BaseCreature { IsDeadPet: true } || Core.TickCount - _lkpExpireTick >= 0)
{
ClearLastKnown();
return false;
}
if (Mobile.Controlled || Mobile.BardPacified || Mobile.BardProvoked || Mobile.FightMode == FightMode.None)
{
return false;
}
if (!Mobile.InRange(target, Mobile.RangePerception) || !Mobile.CanSee(target) ||
!Mobile.InLOS(target) || !Mobile.CanBeHarmful(target, false))
{
return false;
}
DebugSay("There you are!");
Mobile.Combatant = target;
Mobile.FocusMob = null;
Action = ActionType.Combat;
return true;
}
/// <summary>
/// Walks toward the last-seen position until it is in view, reached, timed out, or
/// unreachable. Returns false when the investigation is finished.
/// </summary>
private bool InvestigateLastKnown()
{
if (_lkpTarget == null || Core.TickCount - _investigateStopTick >= 0)
{
return false;
}
if (Mobile.InRange(_lkpLocation, 1) ||
Mobile.InLOS(_lkpLocation) && Mobile.InRange(_lkpLocation, Mobile.RangePerception))
{
DebugSay("They truly disappeared...");
return false;
}
_lkpGoal ??= _lkpLocation;
return MoveToPoint(_lkpGoal, false);
}
private void ClearLastKnown()
{
_lkpTarget = null;
_lkpGoal = null;
_investigating = false;
}
public virtual bool DoActionFlee()
{
var from = Mobile.Combatant;

View file

@ -679,7 +679,7 @@ public class MageAI : BaseAI
Mobile.Combatant = Mobile.FocusMob;
Mobile.FocusMob = null;
}
else if (!Mobile.InRange(c, Mobile.RangePerception * 3))
else if (!Mobile.InRange(c, Mobile.ChaseLeashRange))
{
Mobile.Combatant = null;
}
@ -695,6 +695,23 @@ public class MageAI : BaseAI
}
}
// Geometry (not hiding — CanSee passed above) is blocking the shot: close in until
// line of sight returns. Poisoned mages still fall through to cure.
if (!Mobile.Poisoned && Mobile.Spell?.IsCasting != true && !Mobile.InLOS(c))
{
DebugSay("I cannot see my target, moving to regain line of sight");
if (!MoveTo(c, false, 1))
{
OnFailedMove();
}
_lastTarget = c;
_lastTargetLoc = c.Location;
return true;
}
if (Mobile.TriggerAbility(MonsterAbilityTrigger.CombatAction, c))
{
DebugSay("I used my abilities!");
@ -1018,7 +1035,16 @@ public class MageAI : BaseAI
if (toTarget != null)
{
RunTo(toTarget);
// Without line of sight the stand-off is pointless — close in so the held
// target can be invoked.
if (!Mobile.InLOS(toTarget))
{
MoveTo(toTarget, true, 1);
}
else
{
RunTo(toTarget);
}
}
}

View file

@ -82,7 +82,7 @@ public class MeleeAI : BaseAI
return true;
}
if (!Mobile.InRange(combatant, Mobile.RangePerception * 3))
if (!Mobile.InRange(combatant, Mobile.ChaseLeashRange))
{
Mobile.Combatant = null;
}

View file

@ -660,6 +660,13 @@ namespace Server.Mobiles
[CommandProperty(AccessLevel.GameMaster)]
public int RangePerception { get; set; }
/// <summary>
/// How far a chase may stretch before the creature gives up its combatant. Between
/// RangePerception and this leash it keeps chasing but may switch to closer targets.
/// </summary>
[CommandProperty(AccessLevel.GameMaster)]
public virtual int ChaseLeashRange => RangePerception * 2;
[CommandProperty(AccessLevel.GameMaster)]
public int RangeFight { get; set; }