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

namespace AcDream.Core.Physics;

/// <summary>
/// IWeenieObject implementation for the local player. Provides skill-based
/// run rate and jump velocity calculations.
///
/// Formulas from decompiled acclient.exe, cross-referenced against
/// ACE MovementSystem.GetRunRate and MovementSystem.GetJumpHeight.
/// </summary>
public sealed class PlayerWeenie : IWeenieObject
{
    private int _runSkill;
    private int _jumpSkill;
    private float _burden;

    public PlayerWeenie(int runSkill = 0, int jumpSkill = 0, float burden = 0f)
    {
        _runSkill = runSkill;
        _jumpSkill = jumpSkill;
        _burden = burden;
    }

    public void SetSkills(int runSkill, int jumpSkill)
    {
        _runSkill = runSkill;
        _jumpSkill = jumpSkill;
    }

    public void SetBurden(float burden) => _burden = burden;

    public bool InqRunRate(out float rate)
    {
        rate = GetRunRate(_burden, _runSkill);
        return true;
    }

    public bool InqJumpVelocity(float extent, out float vz)
    {
        float height = GetJumpHeight(_burden, _jumpSkill, extent);
        vz = MathF.Sqrt(height * 19.6f);
        return true;
    }

    public bool CanJump(float extent) => true; // burden/stamina checks deferred

    /// <summary>
    /// RunRate = (burdenMod * (runSkill / (runSkill + 200)) * 11 + 4) / 4
    /// Capped at 4.5 when runSkill >= 800.
    /// Source: decompiled + ACE MovementSystem.GetRunRate
    /// </summary>
    public static float GetRunRate(float burden, int runSkill)
    {
        if (runSkill >= 800) return 18f / 4f;
        float loadMod = GetBurdenMod(burden);
        return (loadMod * ((float)runSkill / (runSkill + 200) * 11f) + 4f) / 4f;
    }

    /// <summary>
    /// JumpHeight = burdenMod * (jumpSkill / (jumpSkill + 1300) * 22.2 + 0.05) * extent
    /// Clamped to minimum 0.35m.
    /// Source: decompiled + ACE MovementSystem.GetJumpHeight
    /// </summary>
    public static float GetJumpHeight(float burden, int jumpSkill, float extent)
    {
        extent = Math.Clamp(extent, 0f, 1f);
        float loadMod = GetBurdenMod(burden);
        float height = loadMod * ((float)jumpSkill / (jumpSkill + 1300f) * 22.2f + 0.05f) * extent;
        return MathF.Max(height, 0.35f);
    }

    /// <summary>
    /// Encumbrance modifier: 1.0 when unloaded, linearly decreasing to 0 at 200%.
    /// Source: decompiled + ACE EncumbranceSystem.GetBurdenMod
    /// </summary>
    public static float GetBurdenMod(float burden)
    {
        if (burden < 1f) return 1f;
        if (burden < 2f) return 2f - burden;
        return 0f;
    }
}