doom-dm/DoomDeathmatch/src/Component/Physics/RigidbodyComponent.cs

using OpenTK.Mathematics;

namespace DoomDeathmatch.Component.Physics;

/// <summary>
/// Represents a rigidbody component that simulates physics behavior such as force, velocity, and acceleration.
/// </summary>
public class RigidbodyComponent : Engine.Scene.Component.Component
{
  /// <summary>
  /// The mass of the rigidbody.
  /// </summary>
  public float Mass { get; set; } = 1.0f;

  /// <summary>
  /// The moment of inertia of the rigidbody.
  /// For simplicity, this assumes a scalar value, suitable for symmetric objects.
  /// </summary>
  public float MomentOfInertia { get; set; } = 1.0f;

  /// <summary>
  /// Indicates whether the rigidbody is static and unaffected by forces.
  /// </summary>
  public bool IsStatic { get; set; } = false;

  /// <summary>
  /// The force currently applied to the rigidbody.
  /// </summary>
  public Vector3 Force
  {
    get => _force;
    set
    {
      if (IsStatic)
      {
        return;
      }

      _force = value;
    }
  }

  /// <summary>
  /// The torque currently applied to the rigidbody.
  /// </summary>
  public Vector3 Torque
  {
    get => _torque;
    set
    {
      if (IsStatic)
      {
        return;
      }

      _torque = value;
    }
  }

  /// <summary>
  /// The velocity of the rigidbody.
  /// </summary>
  public Vector3 Velocity
  {
    get => _velocity;
    set
    {
      if (IsStatic)
      {
        return;
      }

      _velocity = value;
    }
  }

  /// <summary>
  /// The angular velocity of the rigidbody.
  /// </summary>
  public Vector3 AngularVelocity
  {
    get => _angularVelocity;
    set
    {
      if (IsStatic)
      {
        return;
      }

      _angularVelocity = value;
    }
  }

  /// <summary>
  /// The force currently applied to the rigidbody.
  /// </summary>
  private Vector3 _force = Vector3.Zero;

  /// <summary>
  /// The acceleration of the rigidbody.
  /// </summary>
  private Vector3 _acceleration = Vector3.Zero;

  /// <summary>
  /// The velocity of the rigidbody.
  /// </summary>
  private Vector3 _velocity = Vector3.Zero;

  /// <summary>
  /// The torque currently applied to the rigidbody.
  /// </summary>
  private Vector3 _torque = Vector3.Zero;

  /// <summary>
  /// The angular acceleration of the rigidbody.
  /// </summary>
  private Vector3 _angularAcceleration = Vector3.Zero;

  /// <summary>
  /// The angular velocity of the rigidbody.
  /// </summary>
  private Vector3 _angularVelocity = Vector3.Zero;

  public override void PostUpdate(double parDeltaTime)
  {
    if (IsStatic)
    {
      return;
    }

    ApplyForce(parDeltaTime);
    ApplyTorque(parDeltaTime);
  }

  /// <summary>
  /// Applies force to the rigidbody.
  /// </summary>
  /// <param name="parDeltaTime">The time in seconds since the last update.</param>
  private void ApplyForce(double parDeltaTime)
  {
    _acceleration = Force / Mass;
    Velocity += _acceleration * (float)parDeltaTime;
    GameObject.Transform.Translation += Velocity * (float)parDeltaTime;

    Force = Vector3.Zero;
  }

  /// <summary>
  /// Applies torque to the rigidbody.
  /// </summary>
  /// <param name="parDeltaTime">The time in seconds since the last update.</param>
  private void ApplyTorque(double parDeltaTime)
  {
    _angularAcceleration = Torque / MomentOfInertia;
    AngularVelocity += _angularAcceleration * (float)parDeltaTime;

    GameObject.Transform.Rotation *= Quaternion.FromAxisAngle(Vector3.UnitX, AngularVelocity.X * (float)parDeltaTime);
    GameObject.Transform.Rotation *= Quaternion.FromAxisAngle(Vector3.UnitY, AngularVelocity.Y * (float)parDeltaTime);
    GameObject.Transform.Rotation *= Quaternion.FromAxisAngle(Vector3.UnitZ, AngularVelocity.Z * (float)parDeltaTime);

    Torque = Vector3.Zero;
  }
}