Regalis
396 lines
13 KiB
C#
396 lines
13 KiB
C#
/*
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* Farseer Physics Engine:
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* Copyright (c) 2012 Ian Qvist
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*
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* Original source Box2D:
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* Copyright (c) 2006-2011 Erin Catto http://www.box2d.org
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*
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* This software is provided 'as-is', without any express or implied
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* warranty. In no event will the authors be held liable for any damages
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* arising from the use of this software.
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* Permission is granted to anyone to use this software for any purpose,
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* including commercial applications, and to alter it and redistribute it
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* freely, subject to the following restrictions:
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* 1. The origin of this software must not be misrepresented; you must not
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* claim that you wrote the original software. If you use this software
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* in a product, an acknowledgment in the product documentation would be
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* appreciated but is not required.
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* 2. Altered source versions must be plainly marked as such, and must not be
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* misrepresented as being the original software.
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* 3. This notice may not be removed or altered from any source distribution.
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*/
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using System;
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using System.Diagnostics;
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using FarseerPhysics.Common;
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using Microsoft.Xna.Framework;
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namespace FarseerPhysics.Dynamics.Joints
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{
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// Pulley:
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// length1 = norm(p1 - s1)
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// length2 = norm(p2 - s2)
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// C0 = (length1 + ratio * length2)_initial
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// C = C0 - (length1 + ratio * length2)
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// u1 = (p1 - s1) / norm(p1 - s1)
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// u2 = (p2 - s2) / norm(p2 - s2)
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// Cdot = -dot(u1, v1 + cross(w1, r1)) - ratio * dot(u2, v2 + cross(w2, r2))
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// J = -[u1 cross(r1, u1) ratio * u2 ratio * cross(r2, u2)]
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// K = J * invM * JT
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// = invMass1 + invI1 * cross(r1, u1)^2 + ratio^2 * (invMass2 + invI2 * cross(r2, u2)^2)
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/// <summary>
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/// The pulley joint is connected to two bodies and two fixed world points.
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/// The pulley supports a ratio such that:
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/// <![CDATA[length1 + ratio * length2 <= constant]]>
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/// Yes, the force transmitted is scaled by the ratio.
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///
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/// Warning: the pulley joint can get a bit squirrelly by itself. They often
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/// work better when combined with prismatic joints. You should also cover the
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/// the anchor points with static shapes to prevent one side from going to zero length.
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/// </summary>
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public class PulleyJoint : Joint
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{
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// Solver shared
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private float _impulse;
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// Solver temp
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private int _indexA;
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private int _indexB;
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private Vector2 _uA;
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private Vector2 _uB;
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private Vector2 _rA;
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private Vector2 _rB;
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private Vector2 _localCenterA;
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private Vector2 _localCenterB;
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private float _invMassA;
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private float _invMassB;
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private float _invIA;
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private float _invIB;
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private float _mass;
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internal PulleyJoint()
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{
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JointType = JointType.Pulley;
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}
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/// <summary>
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/// Constructor for PulleyJoint.
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/// </summary>
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/// <param name="bodyA">The first body.</param>
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/// <param name="bodyB">The second body.</param>
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/// <param name="anchorA">The anchor on the first body.</param>
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/// <param name="anchorB">The anchor on the second body.</param>
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/// <param name="worldAnchorA">The world anchor for the first body.</param>
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/// <param name="worldAnchorB">The world anchor for the second body.</param>
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/// <param name="ratio">The ratio.</param>
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/// <param name="useWorldCoordinates">Set to true if you are using world coordinates as anchors.</param>
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public PulleyJoint(Body bodyA, Body bodyB, Vector2 anchorA, Vector2 anchorB, Vector2 worldAnchorA, Vector2 worldAnchorB, float ratio, bool useWorldCoordinates = false)
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: base(bodyA, bodyB)
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{
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JointType = JointType.Pulley;
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WorldAnchorA = worldAnchorA;
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WorldAnchorB = worldAnchorB;
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if (useWorldCoordinates)
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{
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LocalAnchorA = BodyA.GetLocalPoint(anchorA);
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LocalAnchorB = BodyB.GetLocalPoint(anchorB);
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Vector2 dA = anchorA - worldAnchorA;
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LengthA = dA.Length();
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Vector2 dB = anchorB - worldAnchorB;
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LengthB = dB.Length();
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}
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else
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{
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LocalAnchorA = anchorA;
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LocalAnchorB = anchorB;
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Vector2 dA = anchorA - BodyA.GetLocalPoint(worldAnchorA);
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LengthA = dA.Length();
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Vector2 dB = anchorB - BodyB.GetLocalPoint(worldAnchorB);
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LengthB = dB.Length();
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}
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Debug.Assert(ratio != 0.0f);
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Debug.Assert(ratio > Settings.Epsilon);
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Ratio = ratio;
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Constant = LengthA + ratio * LengthB;
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_impulse = 0.0f;
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}
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/// <summary>
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/// The local anchor point on BodyA
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/// </summary>
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public Vector2 LocalAnchorA { get; set; }
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/// <summary>
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/// The local anchor point on BodyB
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/// </summary>
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public Vector2 LocalAnchorB { get; set; }
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/// <summary>
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/// Get the first world anchor.
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/// </summary>
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/// <value></value>
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public override sealed Vector2 WorldAnchorA { get; set; }
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/// <summary>
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/// Get the second world anchor.
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/// </summary>
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/// <value></value>
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public override sealed Vector2 WorldAnchorB { get; set; }
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/// <summary>
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/// Get the current length of the segment attached to body1.
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/// </summary>
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/// <value></value>
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public float LengthA { get; set; }
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/// <summary>
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/// Get the current length of the segment attached to body2.
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/// </summary>
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/// <value></value>
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public float LengthB { get; set; }
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/// <summary>
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/// The current length between the anchor point on BodyA and WorldAnchorA
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/// </summary>
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public float CurrentLengthA
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{
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get
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{
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Vector2 p = BodyA.GetWorldPoint(LocalAnchorA);
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Vector2 s = WorldAnchorA;
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Vector2 d = p - s;
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return d.Length();
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}
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}
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/// <summary>
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/// The current length between the anchor point on BodyB and WorldAnchorB
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/// </summary>
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public float CurrentLengthB
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{
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get
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{
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Vector2 p = BodyB.GetWorldPoint(LocalAnchorB);
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Vector2 s = WorldAnchorB;
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Vector2 d = p - s;
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return d.Length();
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}
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}
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/// <summary>
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/// Get the pulley ratio.
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/// </summary>
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/// <value></value>
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public float Ratio { get; set; }
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//FPE note: Only used for serialization.
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internal float Constant { get; set; }
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public override Vector2 GetReactionForce(float invDt)
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{
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Vector2 P = _impulse * _uB;
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return invDt * P;
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}
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public override float GetReactionTorque(float invDt)
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{
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return 0.0f;
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}
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internal override void InitVelocityConstraints(ref SolverData data)
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{
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_indexA = BodyA.IslandIndex;
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_indexB = BodyB.IslandIndex;
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_localCenterA = BodyA._sweep.LocalCenter;
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_localCenterB = BodyB._sweep.LocalCenter;
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_invMassA = BodyA._invMass;
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_invMassB = BodyB._invMass;
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_invIA = BodyA._invI;
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_invIB = BodyB._invI;
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Vector2 cA = data.positions[_indexA].c;
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float aA = data.positions[_indexA].a;
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Vector2 vA = data.velocities[_indexA].v;
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float wA = data.velocities[_indexA].w;
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Vector2 cB = data.positions[_indexB].c;
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float aB = data.positions[_indexB].a;
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Vector2 vB = data.velocities[_indexB].v;
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float wB = data.velocities[_indexB].w;
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Rot qA = new Rot(aA), qB = new Rot(aB);
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_rA = MathUtils.Mul(qA, LocalAnchorA - _localCenterA);
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_rB = MathUtils.Mul(qB, LocalAnchorB - _localCenterB);
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// Get the pulley axes.
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_uA = cA + _rA - WorldAnchorA;
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_uB = cB + _rB - WorldAnchorB;
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float lengthA = _uA.Length();
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float lengthB = _uB.Length();
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if (lengthA > 10.0f * Settings.LinearSlop)
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{
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_uA *= 1.0f / lengthA;
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}
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else
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{
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_uA = Vector2.Zero;
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}
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if (lengthB > 10.0f * Settings.LinearSlop)
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{
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_uB *= 1.0f / lengthB;
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}
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else
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{
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_uB = Vector2.Zero;
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}
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// Compute effective mass.
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float ruA = MathUtils.Cross(_rA, _uA);
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float ruB = MathUtils.Cross(_rB, _uB);
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float mA = _invMassA + _invIA * ruA * ruA;
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float mB = _invMassB + _invIB * ruB * ruB;
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_mass = mA + Ratio * Ratio * mB;
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if (_mass > 0.0f)
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{
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_mass = 1.0f / _mass;
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}
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if (Settings.EnableWarmstarting)
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{
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// Scale impulses to support variable time steps.
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_impulse *= data.step.dtRatio;
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// Warm starting.
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Vector2 PA = -(_impulse) * _uA;
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Vector2 PB = (-Ratio * _impulse) * _uB;
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vA += _invMassA * PA;
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wA += _invIA * MathUtils.Cross(_rA, PA);
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vB += _invMassB * PB;
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wB += _invIB * MathUtils.Cross(_rB, PB);
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}
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else
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{
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_impulse = 0.0f;
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}
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data.velocities[_indexA].v = vA;
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data.velocities[_indexA].w = wA;
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data.velocities[_indexB].v = vB;
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data.velocities[_indexB].w = wB;
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}
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internal override void SolveVelocityConstraints(ref SolverData data)
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{
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Vector2 vA = data.velocities[_indexA].v;
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float wA = data.velocities[_indexA].w;
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Vector2 vB = data.velocities[_indexB].v;
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float wB = data.velocities[_indexB].w;
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Vector2 vpA = vA + MathUtils.Cross(wA, _rA);
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Vector2 vpB = vB + MathUtils.Cross(wB, _rB);
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float Cdot = -Vector2.Dot(_uA, vpA) - Ratio * Vector2.Dot(_uB, vpB);
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float impulse = -_mass * Cdot;
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_impulse += impulse;
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Vector2 PA = -impulse * _uA;
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Vector2 PB = -Ratio * impulse * _uB;
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vA += _invMassA * PA;
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wA += _invIA * MathUtils.Cross(_rA, PA);
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vB += _invMassB * PB;
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wB += _invIB * MathUtils.Cross(_rB, PB);
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data.velocities[_indexA].v = vA;
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data.velocities[_indexA].w = wA;
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data.velocities[_indexB].v = vB;
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data.velocities[_indexB].w = wB;
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}
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internal override bool SolvePositionConstraints(ref SolverData data)
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{
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Vector2 cA = data.positions[_indexA].c;
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float aA = data.positions[_indexA].a;
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Vector2 cB = data.positions[_indexB].c;
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float aB = data.positions[_indexB].a;
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Rot qA = new Rot(aA), qB = new Rot(aB);
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Vector2 rA = MathUtils.Mul(qA, LocalAnchorA - _localCenterA);
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Vector2 rB = MathUtils.Mul(qB, LocalAnchorB - _localCenterB);
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// Get the pulley axes.
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Vector2 uA = cA + rA - WorldAnchorA;
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Vector2 uB = cB + rB - WorldAnchorB;
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float lengthA = uA.Length();
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float lengthB = uB.Length();
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if (lengthA > 10.0f * Settings.LinearSlop)
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{
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uA *= 1.0f / lengthA;
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}
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else
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{
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uA = Vector2.Zero;
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}
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if (lengthB > 10.0f * Settings.LinearSlop)
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{
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uB *= 1.0f / lengthB;
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}
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else
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{
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uB = Vector2.Zero;
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}
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// Compute effective mass.
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float ruA = MathUtils.Cross(rA, uA);
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float ruB = MathUtils.Cross(rB, uB);
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float mA = _invMassA + _invIA * ruA * ruA;
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float mB = _invMassB + _invIB * ruB * ruB;
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float mass = mA + Ratio * Ratio * mB;
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if (mass > 0.0f)
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{
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mass = 1.0f / mass;
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}
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float C = Constant - lengthA - Ratio * lengthB;
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float linearError = Math.Abs(C);
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float impulse = -mass * C;
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Vector2 PA = -impulse * uA;
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Vector2 PB = -Ratio * impulse * uB;
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cA += _invMassA * PA;
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aA += _invIA * MathUtils.Cross(rA, PA);
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cB += _invMassB * PB;
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aB += _invIB * MathUtils.Cross(rB, PB);
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data.positions[_indexA].c = cA;
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data.positions[_indexA].a = aA;
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data.positions[_indexB].c = cB;
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data.positions[_indexB].a = aB;
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return linearError < Settings.LinearSlop;
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}
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}
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} |