acdream/src/AcDream.Core/Physics/RetailObjectActivityGate.cs

using System.Numerics;

namespace AcDream.Core.Physics;

/// <summary>
/// Ports the lifecycle and 96-world-unit Active gate at the head of retail
/// <c>CPhysicsObj::update_object</c> (0x00515D10) plus the inactive branch of
/// <c>UpdateObjectInternal</c> (0x005156B0).
/// </summary>
public static class RetailObjectActivityGate
{
    public const float MaxPhysicsDistance = 96f;

    public static RetailObjectActivityResult Evaluate(
        RetailObjectQuantumClock clock,
        PhysicsBody? body,
        bool lifecycleEligible,
        bool hasPartArray,
        bool isStatic,
        Vector3 objectPosition,
        Vector3? playerPosition,
        double elapsedSeconds)
    {
        ArgumentNullException.ThrowIfNull(clock);

        if (!lifecycleEligible)
        {
            SetActive(clock, body, active: false);
            return RetailObjectActivityResult.Suspended;
        }

        // Retail performs both the 96-unit decision and set_active(1) only
        // while player_object exists. During login/session transitions a
        // missing player preserves the prior Active state; it must not wake a
        // previously distant object.
        if (playerPosition is null)
        {
            if (clock.IsActive)
                return RetailObjectActivityResult.Active;
            clock.Advance(elapsedSeconds);
            return RetailObjectActivityResult.Inactive;
        }

        bool withinActiveBubble = !hasPartArray
            || Vector3.Distance(objectPosition, playerPosition.Value)
                <= MaxPhysicsDistance;
        if (!withinActiveBubble)
        {
            SetActive(clock, body, active: false);
            // Inactive ordinary objects still consume update_time and run
            // their particle/script tail. Those owners tick elsewhere in
            // acdream; consuming the batch here prevents later catch-up.
            clock.Advance(elapsedSeconds);
            return RetailObjectActivityResult.Inactive;
        }

        // CPhysicsObj::set_active(1) (0x0050FC40) is a no-op for Static.
        // Static objects that were initialized or removed from visibility
        // inactive therefore stay on UpdateObjectInternal's particle/script
        // tail instead of entering root physics.
        bool reactivated = false;
        if (!isStatic)
        {
            reactivated = clock.Activate();
            if (body is not null)
                body.TransientState |= TransientStateFlags.Active;
        }

        if (!clock.IsActive)
        {
            clock.Advance(elapsedSeconds);
            return RetailObjectActivityResult.Inactive;
        }

        return reactivated
            ? RetailObjectActivityResult.Reactivated
            : RetailObjectActivityResult.Active;
    }

    private static void SetActive(
        RetailObjectQuantumClock clock,
        PhysicsBody? body,
        bool active)
    {
        if (active)
            clock.Activate();
        else
            clock.Deactivate();

        if (body is not null && !active)
            body.TransientState &= ~TransientStateFlags.Active;
    }
}

public enum RetailObjectActivityResult
{
    Suspended,
    Inactive,
    Reactivated,
    Active,
}