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ModernUO/dev-docs/claude-skills/migrate-from-runuo/migrate-items-mobiles.md
Kamron Batman e07416902a
feat: derive the Running bit from the step pace and fix step-pacing bursts (#2599) 
Stacked on #2594. Fixes jerky creature movement (lich / Fast-bucket melee chases) by choosing the client animation flag from the actual step pace instead of a caller-supplied `run` argument, and fixes three step-pacing defects in the move budget found while verifying it with paired server/client traces.

### Why

The `Direction.Running` bit does nothing for creatures server-side (`Mobile.OnMove` reads it only for the player throttle and stealth reveal). Its whole effect is on the client, which animates each step over a fixed time selected by that bit: walk 400 ms / run 200 ms on foot, 200 / 100 ms mounted. ClassicUO queues up to 5 steps and *drops* the sixth, so a creature stepping every 300 ms while flagged as walking backs the queue up until it snaps forward — the observed jerk.

The `run` argument never carried the one fact that matters (the step interval). RunUO passed `true` in combat / `false` for pets and gated it on `dist > 5`; #2271 flipped every combat site to `false`; pets passed `currentDistance > 2`. None of that is a coherent signal.

### What

**Pace-derived run flag**
- `BaseAI.ShouldRun()`: run iff the effective step delay (move clock + badly-hurt inflation) is shorter than `Movement.WalkFootDelay` / `WalkMountDelay` (mounted or flying) — with a continuity rule: an *isolated* step (taken after standing at least a walk interval) goes out as a walk, because the client renders each step alone and a lone run-flagged step is a 200 ms dart. Only a continuing cadence flags run; a true sprinter (pace under the run interpolation) always runs, since a walk-rendered first step would flood the client's 5-step queue. This reproduces RunUO's close-in feel (its `dist > 5` gate) from first principles.
- `DoMoveImpl` stamps the bit; it is the single place the flag is set.
- `run` removed from `MoveTo`, `WalkMobileRange`, `ApproachTarget`, `MoveToPoint`, `MoveToWithGroup`, `MoveToWithCollisionAvoidance`, the move intent, and `PathFollower.Follow`. All 35 call sites updated. **API change** for custom scripts — documented in the RunUO migration docs (`09-items-mobiles-creatures.md`, `11-api-reference.md`) and `content-patterns.md` § Creature Speeds.

**Move-budget pacing fixes** (each confirmed by UTC-aligned server/client step traces)
- A stall no longer banks catch-up steps: the budget's snap-to-now released up to three steps in ~300 ms when a creature resumed chasing after standing beside its target — rendered as a teleport.
- Debt accrual removed entirely: a step landing sub-period late (think-grid vs budget misalignment during reactive mirroring) kept the remainder and fired a follow-up ~100 ms later — a dart pair. `ConsumeMoveBudget` now paces every step from when it was actually taken; in continuous pursuit the move-wake lands within wheel resolution of the deadline, so the cost is single-digit-ms drift.
- Net effect: a creature can never step faster than its pace, verified across a full chase session (zero sub-pace steps; metronomic 350 ms cadence for a 0.3 s lich).

- Test fixture now runs `Movement.Configure()` (the walk delays were 0 in tests).

### Accepted trade-off

Animal (LOW group) bodies without a run animation slide on their stand frames when flagged as running. Most are slow enough to stay flagged as walking; the client-side fallback is in ClassicUO/ClassicUO#1930.

### Tests

`RunFlagTests`: foot thresholds (0.3 / 0.125 run; 0.4 / 0.45 / 1.05 walk), flying uses the mount threshold, badly-hurt inflation flips a 0.35 s creature back to walk, a real `DoMove` stamps the bit, isolated steps drop to walk (sprinters keep running), a stall restarts the cadence with no banked steps, and a late step earns no quicker follow-up. Full suite: 837 Server + 747 UOContent green.
2026-08-30 16:48:52 -07:00

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name description
migrate-items-mobiles Trigger: when converting RunUO Item, Mobile, or BaseCreature subclasses to ModernUO. Most common migration task. Covers: complete item/creature conversion combining serialization, timers, properties, naming.

RunUO -> ModernUO Item/Mobile/Creature Migration

When This Activates

  • Converting any Item subclass from RunUO
  • Converting any Mobile/BaseCreature subclass
  • This is the most common migration task -- combines all other systems

Item Conversion Checklist

  1. Foundation: file-scoped namespace, using ModernUO.Serialization;
  2. Class: add [SerializationGenerator(N, false)] (N = old version + 1, false if old Deserialize used ReadInt()), add partial
  3. Fields: m_X -> [SerializableField(N)] _x with [SerializedCommandProperty]
  4. Add [InvalidateProperties] where RunUO setter called InvalidateProperties()
  5. Delete: Serial constructor, Serialize, Deserialize
  6. [Constructable] -> [Constructible]
  7. Name = "text" -> public override string DefaultName => "text";
  8. Timers: nested class -> Timer.StartTimer() + TimerExecutionToken + [AfterDeserialization] + OnAfterDelete
  9. Properties: GetProperties(ObjectPropertyList) -> GetProperties(IPropertyList), apply string hole rule
  10. Context menus: List<ContextMenuEntry> -> ref PooledRefList<ContextMenuEntry>

Creature-Specific Changes

  • [CorpseName("...")] attribute -> public override string CorpseName => "...";
  • BaseCreature(AI, Fight, 10, 1, 0.2, 0.4) -> BaseCreature(AI, Fight) (extra params default)
  • Name = "text" -> public override string DefaultName => "text";
  • Expression-bodied overrides: public override int Meat { get { return 1; } } -> public override int Meat => 1;
  • AI movement calls lose the run flag: MoveTo(m, true, range) -> MoveTo(m, range) (also WalkMobileRange, ApproachTarget, MoveToPoint, PathFollower.Follow); the Running bit is derived from step pace -> dev-docs/runuo-migration-docs/09-items-mobiles-creatures.md § AI Movement

Anti-Patterns

  • Using _field-- instead of Property-- (bypasses MarkDirty tracking)
  • Forgetting [AfterDeserialization] for timer restoration
  • Forgetting OnAfterDelete() for timer cancellation

See Also

  • dev-docs/runuo-migration-docs/09-items-mobiles-creatures.md -- detailed migration with before/after examples
  • dev-docs/content-patterns.md -- ModernUO content templates
  • dev-docs/claude-skills/modernuo-content-patterns.md -- ModernUO content skill
  • dev-docs/claude-skills/modernuo-serialization.md -- serialization patterns
  • dev-docs/claude-skills/modernuo-timers.md -- timer patterns