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335 lines
10 KiB
C#
335 lines
10 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.Numerics;
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using Robust.Shared.Configuration;
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using Robust.Shared.GameObjects;
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using Robust.Shared.IoC;
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using Robust.Shared.Maths;
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using Robust.Shared.Physics.Components;
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using Robust.Shared.Physics.Systems;
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using Robust.Shared.Serialization;
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using Robust.Shared.Serialization.Manager.Attributes;
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using Robust.Shared.ViewVariables;
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namespace Robust.Shared.Physics.Dynamics.Joints;
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// Point-to-point constraint
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// Cdot = v2 - v1
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// = v2 + cross(w2, r2) - v1 - cross(w1, r1)
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// J = [-I -r1_skew I r2_skew ]
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// Identity used:
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// w k % (rx i + ry j) = w * (-ry i + rx j)
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// Angle constraint
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// Cdot = w2 - w1
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// J = [0 0 -1 0 0 1]
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// K = invI1 + invI2
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[Serializable, NetSerializable]
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public sealed class FrictionJointState : JointState
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{
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public float MaxForce { get; }
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public float MaxTorque { get; }
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public override Joint GetJoint()
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{
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return new FrictionJoint(this);
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}
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}
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/// <summary>
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/// Friction joint. This is used for top-down friction.
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/// It provides 2D translational friction and angular friction.
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/// </summary>
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public sealed partial class FrictionJoint : Joint, IEquatable<FrictionJoint>
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{
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// Solver shared
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private Vector2 _linearImpulse;
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private float _angularImpulse;
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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 _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 _angularMass;
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private Vector2[] _linearMass = new Vector2[2];
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public override JointType JointType => JointType.Friction;
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/// <summary>
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/// The maximum friction force in N.
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/// </summary>
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[ViewVariables(VVAccess.ReadWrite)]
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[DataField("maxForce")]
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public float MaxForce { get; set; }
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/// <summary>
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/// The maximum friction torque in N-m.
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/// </summary>
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[ViewVariables(VVAccess.ReadWrite)]
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[DataField("maxTorque")]
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public float MaxTorque { get; set; }
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public FrictionJoint() {}
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public FrictionJoint(EntityUid uidA, EntityUid uidB, Vector2 anchorA, Vector2 anchorB)
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: base(uidA, uidB)
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{
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LocalAnchorA = anchorA;
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LocalAnchorB = anchorB;
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}
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internal FrictionJoint(FrictionJointState state) : base(state)
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{
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MaxForce = state.MaxForce;
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MaxTorque = state.MaxTorque;
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}
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public override JointState GetState()
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{
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var frictionState = new FrictionJointState();
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base.GetState(frictionState);
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return frictionState;
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}
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internal override void ApplyState(JointState state)
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{
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base.ApplyState(state);
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if (state is not FrictionJointState frictionState) return;
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MaxForce = frictionState.MaxForce;
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MaxTorque = frictionState.MaxTorque;
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}
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public override Vector2 GetReactionForce(float invDt)
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{
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return _linearImpulse * invDt;
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}
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public override float GetReactionTorque(float invDt)
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{
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return invDt * _angularImpulse;
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}
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internal override void InitVelocityConstraints(
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in SolverData data,
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in SharedPhysicsSystem.IslandData island,
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PhysicsComponent bodyA,
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PhysicsComponent bodyB,
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Vector2[] positions,
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float[] angles,
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Vector2[] linearVelocities,
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float[] angularVelocities)
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{
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var offset = island.Offset;
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_indexA = bodyA.IslandIndex[island.Index];
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_indexB = bodyB.IslandIndex[island.Index];
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_localCenterA = bodyA.LocalCenter;
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_localCenterB = bodyB.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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float aA = angles[_indexA];
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Vector2 vA = linearVelocities[offset + _indexA];
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float wA = angularVelocities[offset + _indexA];
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float aB = angles[_indexB];
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Vector2 vB = linearVelocities[offset + _indexB];
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float wB = angularVelocities[offset + _indexB];
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Quaternion2D qA = new(aA), qB = new(aB);
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// Compute the effective mass matrix.
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_rA = Transform.Mul(qA, LocalAnchorA - _localCenterA);
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_rB = Transform.Mul(qB, LocalAnchorB - _localCenterB);
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// J = [-I -r1_skew I r2_skew]
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// [ 0 -1 0 1]
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// r_skew = [-ry; rx]
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// Matlab
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// K = [ mA+r1y^2*iA+mB+r2y^2*iB, -r1y*iA*r1x-r2y*iB*r2x, -r1y*iA-r2y*iB]
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// [ -r1y*iA*r1x-r2y*iB*r2x, mA+r1x^2*iA+mB+r2x^2*iB, r1x*iA+r2x*iB]
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// [ -r1y*iA-r2y*iB, r1x*iA+r2x*iB, iA+iB]
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float mA = _invMassA, mB = _invMassB;
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float iA = _invIA, iB = _invIB;
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Span<Vector2> K = stackalloc Vector2[2];
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K[0].X = mA + mB + iA * _rA.Y * _rA.Y + iB * _rB.Y * _rB.Y;
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K[0].Y = -iA * _rA.X * _rA.Y - iB * _rB.X * _rB.Y;
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K[1].X = K[0].Y;
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K[1].Y = mA + mB + iA * _rA.X * _rA.X + iB * _rB.X * _rB.X;
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Vector4Helpers.Inverse(K);
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_angularMass = iA + iB;
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if (_angularMass > 0.0f)
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{
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_angularMass = 1.0f / _angularMass;
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}
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// ReSharper disable once ConditionIsAlwaysTrueOrFalse
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if (data.WarmStarting)
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{
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// Scale impulses to support a variable time step.
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_linearImpulse *= data.DtRatio;
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_angularImpulse *= data.DtRatio;
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Vector2 P = new Vector2(_linearImpulse.X, _linearImpulse.Y);
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vA -= P * mA;
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wA -= iA * (Vector2Helpers.Cross(_rA, P) + _angularImpulse);
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vB += P * mB;
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wB += iB * (Vector2Helpers.Cross(_rB, P) + _angularImpulse);
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}
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else
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{
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_linearImpulse = Vector2.Zero;
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_angularImpulse = 0.0f;
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}
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linearVelocities[offset + _indexA] = vA;
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angularVelocities[offset + _indexA] = wA;
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linearVelocities[offset + _indexB] = vB;
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angularVelocities[offset + _indexB] = wB;
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}
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internal override void SolveVelocityConstraints(
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in SolverData data,
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in SharedPhysicsSystem.IslandData island,
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Vector2[] linearVelocities,
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float[] angularVelocities)
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{
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var offset = island.Offset;
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Vector2 vA = linearVelocities[offset + _indexA];
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float wA = angularVelocities[offset + _indexA];
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Vector2 vB = linearVelocities[offset + _indexB];
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float wB = angularVelocities[offset + _indexB];
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float mA = _invMassA, mB = _invMassB;
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float iA = _invIA, iB = _invIB;
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float h = data.FrameTime;
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// Solve angular friction
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{
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float Cdot = wB - wA;
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float impulse = -_angularMass * Cdot;
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float oldImpulse = _angularImpulse;
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float maxImpulse = h * MaxTorque;
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_angularImpulse = Math.Clamp(_angularImpulse + impulse, -maxImpulse, maxImpulse);
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impulse = _angularImpulse - oldImpulse;
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wA -= iA * impulse;
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wB += iB * impulse;
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}
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// Solve linear friction
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{
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Vector2 Cdot = vB + Vector2Helpers.Cross(wB, _rB) - vA - Vector2Helpers.Cross(wA, _rA);
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Vector2 impulse = -Transform.Mul(_linearMass, Cdot);
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Vector2 oldImpulse = _linearImpulse;
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_linearImpulse += impulse;
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float maxImpulse = h * MaxForce;
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if (_linearImpulse.LengthSquared() > maxImpulse * maxImpulse)
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{
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_linearImpulse = _linearImpulse.Normalized();
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_linearImpulse *= maxImpulse;
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}
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impulse = _linearImpulse - oldImpulse;
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vA -= impulse * mA;
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wA -= iA * Vector2Helpers.Cross(_rA, impulse);
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vB += impulse * mB;
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wB += iB * Vector2Helpers.Cross(_rB, impulse);
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}
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linearVelocities[offset + _indexA] = vA;
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angularVelocities[offset + _indexA] = wA;
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linearVelocities[offset + _indexB] = vB;
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angularVelocities[offset + _indexB] = wB;
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}
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internal override bool SolvePositionConstraints(
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in SolverData data,
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Vector2[] positions,
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float[] angles)
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{
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return true;
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}
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public override Joint Clone(EntityUid uidA, EntityUid uidB)
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{
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var friction = new FrictionJoint(uidA, uidB, LocalAnchorA, LocalAnchorB)
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{
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Enabled = Enabled,
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MaxTorque = MaxTorque,
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MaxForce = MaxForce,
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_linearImpulse = _linearImpulse,
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_angularImpulse = _angularImpulse,
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Breakpoint = Breakpoint
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};
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return friction;
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}
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public override void CopyTo(Joint original)
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{
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if (original is not FrictionJoint friction)
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return;
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friction.Enabled = Enabled;
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friction.MaxTorque = MaxTorque;
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friction.MaxForce = MaxForce;
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friction._linearImpulse = _linearImpulse;
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friction._angularImpulse = _angularImpulse;
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friction.Breakpoint = Breakpoint;
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}
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public bool Equals(FrictionJoint? other)
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{
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if (ReferenceEquals(null, other)) return false;
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if (ReferenceEquals(this, other)) return true;
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if (!base.Equals(other)) return false;
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return MathHelper.CloseTo(MaxForce, other.MaxForce) &&
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MathHelper.CloseTo(MaxTorque, other.MaxTorque);
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}
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}
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