261 lines
8.3 KiB
C#
261 lines
8.3 KiB
C#
/*
|
|
* Farseer Physics Engine:
|
|
* Copyright (c) 2012 Ian Qvist
|
|
*
|
|
* Original source Box2D:
|
|
* Copyright (c) 2006-2011 Erin Catto http://www.box2d.org
|
|
*
|
|
* This software is provided 'as-is', without any express or implied
|
|
* warranty. In no event will the authors be held liable for any damages
|
|
* arising from the use of this software.
|
|
* Permission is granted to anyone to use this software for any purpose,
|
|
* including commercial applications, and to alter it and redistribute it
|
|
* freely, subject to the following restrictions:
|
|
* 1. The origin of this software must not be misrepresented; you must not
|
|
* claim that you wrote the original software. If you use this software
|
|
* in a product, an acknowledgment in the product documentation would be
|
|
* appreciated but is not required.
|
|
* 2. Altered source versions must be plainly marked as such, and must not be
|
|
* misrepresented as being the original software.
|
|
* 3. This notice may not be removed or altered from any source distribution.
|
|
*/
|
|
|
|
using System.Diagnostics;
|
|
using FarseerPhysics.Common;
|
|
using Microsoft.Xna.Framework;
|
|
|
|
namespace FarseerPhysics.Dynamics.Joints
|
|
{
|
|
// p = attached point, m = mouse point
|
|
// C = p - m
|
|
// Cdot = v
|
|
// = v + cross(w, r)
|
|
// J = [I r_skew]
|
|
// Identity used:
|
|
// w k % (rx i + ry j) = w * (-ry i + rx j)
|
|
|
|
/// <summary>
|
|
/// A mouse joint is used to make a point on a body track a
|
|
/// specified world point. This a soft constraint with a maximum
|
|
/// force. This allows the constraint to stretch and without
|
|
/// applying huge forces.
|
|
/// NOTE: this joint is not documented in the manual because it was
|
|
/// developed to be used in the testbed. If you want to learn how to
|
|
/// use the mouse joint, look at the testbed.
|
|
/// </summary>
|
|
public class FixedMouseJoint : Joint
|
|
{
|
|
private Vector2 _worldAnchor;
|
|
private float _frequency;
|
|
private float _dampingRatio;
|
|
private float _beta;
|
|
|
|
// Solver shared
|
|
private Vector2 _impulse;
|
|
private float _maxForce;
|
|
private float _gamma;
|
|
|
|
// Solver temp
|
|
private int _indexA;
|
|
private Vector2 _rA;
|
|
private Vector2 _localCenterA;
|
|
private float _invMassA;
|
|
private float _invIA;
|
|
private Mat22 _mass;
|
|
private Vector2 _C;
|
|
|
|
/// <summary>
|
|
/// This requires a world target point,
|
|
/// tuning parameters, and the time step.
|
|
/// </summary>
|
|
/// <param name="body">The body.</param>
|
|
/// <param name="worldAnchor">The target.</param>
|
|
public FixedMouseJoint(Body body, Vector2 worldAnchor)
|
|
: base(body)
|
|
{
|
|
JointType = JointType.FixedMouse;
|
|
Frequency = 5.0f;
|
|
DampingRatio = 0.7f;
|
|
MaxForce = 1000 * body.Mass;
|
|
|
|
Debug.Assert(worldAnchor.IsValid());
|
|
|
|
_worldAnchor = worldAnchor;
|
|
LocalAnchorA = MathUtils.MulT(BodyA._xf, worldAnchor);
|
|
}
|
|
|
|
/// <summary>
|
|
/// The local anchor point on BodyA
|
|
/// </summary>
|
|
public Vector2 LocalAnchorA { get; set; }
|
|
|
|
public override Vector2 WorldAnchorA
|
|
{
|
|
get { return BodyA.GetWorldPoint(LocalAnchorA); }
|
|
set { LocalAnchorA = BodyA.GetLocalPoint(value); }
|
|
}
|
|
|
|
public override Vector2 WorldAnchorB
|
|
{
|
|
get { return _worldAnchor; }
|
|
set
|
|
{
|
|
WakeBodies();
|
|
_worldAnchor = value;
|
|
}
|
|
}
|
|
|
|
/// <summary>
|
|
/// The maximum constraint force that can be exerted
|
|
/// to move the candidate body. Usually you will express
|
|
/// as some multiple of the weight (multiplier * mass * gravity).
|
|
/// </summary>
|
|
public float MaxForce
|
|
{
|
|
get { return _maxForce; }
|
|
set
|
|
{
|
|
Debug.Assert(MathUtils.IsValid(value) && value >= 0.0f);
|
|
_maxForce = value;
|
|
}
|
|
}
|
|
|
|
/// <summary>
|
|
/// The response speed.
|
|
/// </summary>
|
|
public float Frequency
|
|
{
|
|
get { return _frequency; }
|
|
set
|
|
{
|
|
Debug.Assert(MathUtils.IsValid(value) && value >= 0.0f);
|
|
_frequency = value;
|
|
}
|
|
}
|
|
|
|
/// <summary>
|
|
/// The damping ratio. 0 = no damping, 1 = critical damping.
|
|
/// </summary>
|
|
public float DampingRatio
|
|
{
|
|
get { return _dampingRatio; }
|
|
set
|
|
{
|
|
Debug.Assert(MathUtils.IsValid(value) && value >= 0.0f);
|
|
_dampingRatio = value;
|
|
}
|
|
}
|
|
|
|
public override Vector2 GetReactionForce(float invDt)
|
|
{
|
|
return invDt * _impulse;
|
|
}
|
|
|
|
public override float GetReactionTorque(float invDt)
|
|
{
|
|
return invDt * 0.0f;
|
|
}
|
|
|
|
internal override void InitVelocityConstraints(ref SolverData data)
|
|
{
|
|
_indexA = BodyA.IslandIndex;
|
|
_localCenterA = BodyA._sweep.LocalCenter;
|
|
_invMassA = BodyA._invMass;
|
|
_invIA = BodyA._invI;
|
|
|
|
Vector2 cA = data.positions[_indexA].c;
|
|
float aA = data.positions[_indexA].a;
|
|
Vector2 vA = data.velocities[_indexA].v;
|
|
float wA = data.velocities[_indexA].w;
|
|
|
|
Rot qA = new Rot(aA);
|
|
|
|
float mass = BodyA.Mass;
|
|
|
|
// Frequency
|
|
float omega = 2.0f * Settings.Pi * Frequency;
|
|
|
|
// Damping coefficient
|
|
float d = 2.0f * mass * DampingRatio * omega;
|
|
|
|
// Spring stiffness
|
|
float k = mass * (omega * omega);
|
|
|
|
// magic formulas
|
|
// gamma has units of inverse mass.
|
|
// beta has units of inverse time.
|
|
float h = data.step.dt;
|
|
Debug.Assert(d + h * k > Settings.Epsilon);
|
|
_gamma = h * (d + h * k);
|
|
if (_gamma != 0.0f)
|
|
{
|
|
_gamma = 1.0f / _gamma;
|
|
}
|
|
|
|
_beta = h * k * _gamma;
|
|
|
|
// Compute the effective mass matrix.
|
|
_rA = MathUtils.Mul(qA, LocalAnchorA - _localCenterA);
|
|
// K = [(1/m1 + 1/m2) * eye(2) - skew(r1) * invI1 * skew(r1) - skew(r2) * invI2 * skew(r2)]
|
|
// = [1/m1+1/m2 0 ] + invI1 * [r1.Y*r1.Y -r1.X*r1.Y] + invI2 * [r1.Y*r1.Y -r1.X*r1.Y]
|
|
// [ 0 1/m1+1/m2] [-r1.X*r1.Y r1.X*r1.X] [-r1.X*r1.Y r1.X*r1.X]
|
|
Mat22 K = new Mat22();
|
|
K.ex.X = _invMassA + _invIA * _rA.Y * _rA.Y + _gamma;
|
|
K.ex.Y = -_invIA * _rA.X * _rA.Y;
|
|
K.ey.X = K.ex.Y;
|
|
K.ey.Y = _invMassA + _invIA * _rA.X * _rA.X + _gamma;
|
|
|
|
_mass = K.Inverse;
|
|
|
|
_C = cA + _rA - _worldAnchor;
|
|
_C *= _beta;
|
|
|
|
// Cheat with some damping
|
|
wA *= 0.98f;
|
|
|
|
if (Settings.EnableWarmstarting)
|
|
{
|
|
_impulse *= data.step.dtRatio;
|
|
vA += _invMassA * _impulse;
|
|
wA += _invIA * MathUtils.Cross(_rA, _impulse);
|
|
}
|
|
else
|
|
{
|
|
_impulse = Vector2.Zero;
|
|
}
|
|
|
|
data.velocities[_indexA].v = vA;
|
|
data.velocities[_indexA].w = wA;
|
|
}
|
|
|
|
internal override void SolveVelocityConstraints(ref SolverData data)
|
|
{
|
|
Vector2 vA = data.velocities[_indexA].v;
|
|
float wA = data.velocities[_indexA].w;
|
|
|
|
// Cdot = v + cross(w, r)
|
|
Vector2 Cdot = vA + MathUtils.Cross(wA, _rA);
|
|
Vector2 impulse = MathUtils.Mul(ref _mass, -(Cdot + _C + _gamma * _impulse));
|
|
|
|
Vector2 oldImpulse = _impulse;
|
|
_impulse += impulse;
|
|
float maxImpulse = data.step.dt * MaxForce;
|
|
if (_impulse.LengthSquared() > maxImpulse * maxImpulse)
|
|
{
|
|
_impulse *= maxImpulse / _impulse.Length();
|
|
}
|
|
impulse = _impulse - oldImpulse;
|
|
|
|
vA += _invMassA * impulse;
|
|
wA += _invIA * MathUtils.Cross(_rA, impulse);
|
|
|
|
data.velocities[_indexA].v = vA;
|
|
data.velocities[_indexA].w = wA;
|
|
}
|
|
|
|
internal override bool SolvePositionConstraints(ref SolverData data)
|
|
{
|
|
return true;
|
|
}
|
|
}
|
|
} |