axiosengine/axios/Controllers/BuoyancyController.cs

135 lines
5.2 KiB
C#
Raw Normal View History

2012-03-19 23:57:59 +00:00
using System.Collections.Generic;
using FarseerPhysics.Collision;
using FarseerPhysics.Collision.Shapes;
using FarseerPhysics.Dynamics;
using Microsoft.Xna.Framework;
namespace FarseerPhysics.Controllers
{
public sealed class BuoyancyController : Controller
{
/// <summary>
/// Controls the rotational drag that the fluid exerts on the bodies within it. Use higher values will simulate thick fluid, like honey, lower values to
/// simulate water-like fluids.
/// </summary>
public float AngularDragCoefficient;
/// <summary>
/// Density of the fluid. Higher values will make things more buoyant, lower values will cause things to sink.
/// </summary>
public float Density;
/// <summary>
/// Controls the linear drag that the fluid exerts on the bodies within it. Use higher values will simulate thick fluid, like honey, lower values to
/// simulate water-like fluids.
/// </summary>
public float LinearDragCoefficient;
/// <summary>
/// Acts like waterflow. Defaults to 0,0.
/// </summary>
public Vector2 Velocity;
private AABB _container;
private Vector2 _gravity;
private Vector2 _normal;
private float _offset;
private Dictionary<int, Body> _uniqueBodies = new Dictionary<int, Body>();
/// <summary>
/// Initializes a new instance of the <see cref="BuoyancyController"/> class.
/// </summary>
/// <param name="container">Only bodies inside this AABB will be influenced by the controller</param>
/// <param name="density">Density of the fluid</param>
/// <param name="linearDragCoefficient">Linear drag coefficient of the fluid</param>
/// <param name="rotationalDragCoefficient">Rotational drag coefficient of the fluid</param>
/// <param name="gravity">The direction gravity acts. Buoyancy force will act in opposite direction of gravity.</param>
public BuoyancyController(AABB container, float density, float linearDragCoefficient,
float rotationalDragCoefficient, Vector2 gravity)
: base(ControllerType.BuoyancyController)
{
Container = container;
_normal = new Vector2(0, 1);
Density = density;
LinearDragCoefficient = linearDragCoefficient;
AngularDragCoefficient = rotationalDragCoefficient;
_gravity = gravity;
}
public AABB Container
{
get { return _container; }
set
{
_container = value;
_offset = _container.UpperBound.Y;
}
}
public override void Update(float dt)
{
_uniqueBodies.Clear();
World.QueryAABB(fixture =>
{
if (fixture.Body.IsStatic || !fixture.Body.Awake)
return true;
if (!_uniqueBodies.ContainsKey(fixture.Body.BodyId))
_uniqueBodies.Add(fixture.Body.BodyId, fixture.Body);
return true;
}, ref _container);
foreach (KeyValuePair<int, Body> kv in _uniqueBodies)
{
Body body = kv.Value;
Vector2 areac = Vector2.Zero;
Vector2 massc = Vector2.Zero;
float area = 0;
float mass = 0;
for (int j = 0; j < body.FixtureList.Count; j++)
{
Fixture fixture = body.FixtureList[j];
if (fixture.Shape.ShapeType != ShapeType.Polygon && fixture.Shape.ShapeType != ShapeType.Circle)
continue;
Shape shape = fixture.Shape;
Vector2 sc;
float sarea = shape.ComputeSubmergedArea(_normal, _offset, body.Xf, out sc);
area += sarea;
areac.X += sarea * sc.X;
areac.Y += sarea * sc.Y;
mass += sarea * shape.Density;
massc.X += sarea * sc.X * shape.Density;
massc.Y += sarea * sc.Y * shape.Density;
}
areac.X /= area;
areac.Y /= area;
massc.X /= mass;
massc.Y /= mass;
if (area < Settings.Epsilon)
continue;
//Buoyancy
Vector2 buoyancyForce = -Density * area * _gravity;
body.ApplyForce(buoyancyForce, massc);
//Linear drag
Vector2 dragForce = body.GetLinearVelocityFromWorldPoint(areac) - Velocity;
dragForce *= -LinearDragCoefficient * area;
body.ApplyForce(dragForce, areac);
//Angular drag
body.ApplyTorque(-body.Inertia / body.Mass * area * body.AngularVelocity * AngularDragCoefficient);
}
}
}
}