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
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7 changed files with 277 additions and 38 deletions
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@ -26,11 +26,25 @@ namespace Server.Mobiles;
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public abstract partial class BaseAI
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{
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// Last-known-position tracking: recorded while the combatant is in LOS; drives the
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// guard-time investigation and the instant re-engage.
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private const int GuardGraceDuration = 10_000;
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private const int LkpFreshDuration = 30_000;
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private const int InvestigateDuration = 15_000;
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private ActionType _action;
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public long _nextDetectHidden;
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public DateTime _lastOrder = DateTime.MinValue;
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public Mobile _commandIssuer;
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private Mobile _lkpTarget;
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private Point3D _lkpLocation;
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private IPoint3D _lkpGoal; // boxed _lkpLocation handed to the PathFollower
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private long _lkpExpireTick;
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private long _guardStopTick;
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private long _investigateStopTick;
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private bool _investigating;
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public PathFollower Path { get; protected set; }
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public AITimer AITimer { get; }
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public long NextMove { get; set; }
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@ -233,6 +247,15 @@ public abstract partial class BaseAI
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return true;
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}
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if (_action == ActionType.Combat)
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{
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UpdateLastKnownLocation();
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}
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else if (_action is ActionType.Wander or ActionType.Guard)
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{
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TryReengageLastKnown();
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}
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switch (Action)
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{
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case ActionType.Wander:
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@ -323,6 +346,15 @@ public abstract partial class BaseAI
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{
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Mobile.Warmode = true;
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Mobile.Combatant = null;
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// Investigate a fresh last-seen position that is not already in view; the guard
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// grace period begins once the investigation ends.
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_investigating = _lkpTarget != null && Core.TickCount - _lkpExpireTick < 0 &&
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!(Mobile.InRange(_lkpLocation, 1) ||
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Mobile.InLOS(_lkpLocation) && Mobile.InRange(_lkpLocation, Mobile.RangePerception));
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_investigateStopTick = Core.TickCount + InvestigateDuration;
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_guardStopTick = Core.TickCount + GuardGraceDuration;
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_lkpGoal = null;
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}
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private void HandleFleeAction()
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@ -453,18 +485,118 @@ public abstract partial class BaseAI
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public virtual bool DoActionGuard()
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{
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if (Mobile.Combatant == null)
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if (_investigating)
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{
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DebugSay("No threats found. Going home...");
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Action = ActionType.Wander;
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if (InvestigateLastKnown())
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{
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return true;
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}
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_investigating = false;
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_guardStopTick = Core.TickCount + GuardGraceDuration;
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}
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DebugSay("I stopped being on guard.");
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if (Core.TickCount - _guardStopTick < 0)
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{
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DebugSay("I am on guard.");
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if (Utility.Random(8) == 0)
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{
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Mobile.Direction = (Direction)Utility.Random(8);
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}
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return true;
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}
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DebugSay("I stopped being on guard. Going home...");
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Action = ActionType.Wander;
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return true;
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}
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/// <summary>
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/// Records the combatant's position while it is visible and in line of sight.
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/// </summary>
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private void UpdateLastKnownLocation()
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{
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var combatant = Mobile.Combatant;
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if (combatant?.Deleted == false && combatant.Map == Mobile.Map &&
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Mobile.CanSee(combatant) && Mobile.InLOS(combatant))
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{
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_lkpTarget = combatant;
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_lkpLocation = combatant.Location;
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_lkpExpireTick = Core.TickCount + LkpFreshDuration;
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}
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}
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/// <summary>
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/// Re-engages the last-seen target when it returns to view within perception range,
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/// bypassing the reacquire throttle.
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/// </summary>
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private bool TryReengageLastKnown()
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{
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var target = _lkpTarget;
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if (target == null)
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{
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return false;
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}
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if (target.Deleted || !target.Alive || target.Map != Mobile.Map ||
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target is BaseCreature { IsDeadPet: true } || Core.TickCount - _lkpExpireTick >= 0)
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{
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ClearLastKnown();
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return false;
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}
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if (Mobile.Controlled || Mobile.BardPacified || Mobile.BardProvoked || Mobile.FightMode == FightMode.None)
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{
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return false;
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}
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if (!Mobile.InRange(target, Mobile.RangePerception) || !Mobile.CanSee(target) ||
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!Mobile.InLOS(target) || !Mobile.CanBeHarmful(target, false))
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{
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return false;
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}
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DebugSay("There you are!");
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Mobile.Combatant = target;
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Mobile.FocusMob = null;
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Action = ActionType.Combat;
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return true;
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}
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/// <summary>
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/// Walks toward the last-seen position until it is in view, reached, timed out, or
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/// unreachable. Returns false when the investigation is finished.
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/// </summary>
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private bool InvestigateLastKnown()
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{
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if (_lkpTarget == null || Core.TickCount - _investigateStopTick >= 0)
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{
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return false;
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}
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if (Mobile.InRange(_lkpLocation, 1) ||
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Mobile.InLOS(_lkpLocation) && Mobile.InRange(_lkpLocation, Mobile.RangePerception))
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{
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DebugSay("They truly disappeared...");
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return false;
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}
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_lkpGoal ??= _lkpLocation;
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return MoveToPoint(_lkpGoal, false);
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}
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private void ClearLastKnown()
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{
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_lkpTarget = null;
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_lkpGoal = null;
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_investigating = false;
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}
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public virtual bool DoActionFlee()
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{
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var from = Mobile.Combatant;
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