public void Solve(ref TimeStep step, ref FPVector2 gravity)
{
FP h = step.dt;
// Integrate velocities and apply damping. Initialize the body state.
for (int i = 0; i < BodyCount; ++i)
{
Body b = Bodies[i];
FPVector2 c = b._sweep.C;
FP a = b._sweep.A;
FPVector2 v = b._linearVelocity;
FP w = b._angularVelocity;
// Store positions for continuous collision.
b._sweep.C0 = b._sweep.C;
b._sweep.A0 = b._sweep.A;
if (b.BodyType == BodyType.Dynamic)
{
// Integrate velocities.
// FPE: Only apply gravity if the body wants it.
if (b.IgnoreGravity)
{
v += h * (b._invMass * b._force);
}
else
{
v += h * (b.GravityScale * gravity + b._invMass * b._force);
}
w += h * b._invI * b._torque;
// Apply damping.
// ODE: dv/dt + c * v = 0
// Solution: v(t) = v0 * exp(-c * t)
// Time step: v(t + dt) = v0 * exp(-c * (t + dt)) = v0 * exp(-c * t) * exp(-c * dt) = v * exp(-c * dt)
// v2 = exp(-c * dt) * v1
// Taylor expansion:
// v2 = (1.0f - c * dt) * v1
//v *= MathUtils.Clamp(1.0f - h * b.LinearDamping, 0.0f, 1.0f);
//w *= MathUtils.Clamp(1.0f - h * b.AngularDamping, 0.0f, 1.0f);
v *= 1 / (1 + h * b.LinearDamping);
w *= 1 / (1 + h * b.AngularDamping);
}
_positions[i].c = c;
_positions[i].a = a;
_velocities[i].v = v;
_velocities[i].w = w;
}
// Solver data
SolverData solverData = new SolverData();
solverData.step = step;
solverData.positions = _positions;
solverData.velocities = _velocities;
_contactSolver.Reset(step, ContactCount, _contacts, _positions, _velocities);
_contactSolver.InitializeVelocityConstraints();
if (Settings.EnableWarmstarting)
{
_contactSolver.WarmStart();
}
for (int i = 0; i < JointCount; ++i)
{
if (_joints[i].Enabled)
{
_joints[i].InitVelocityConstraints(ref solverData);
}
}
// Solve velocity constraints.
for (int i = 0; i < Settings.VelocityIterations; ++i)
{
for (int j = 0; j < JointCount; ++j)
{
Joint2D joint = _joints[j];
if (!joint.Enabled)
{
continue;
}
joint.SolveVelocityConstraints(ref solverData);
joint.Validate(step.inv_dt);
}
_contactSolver.SolveVelocityConstraints();
}
// Store impulses for warm starting.
_contactSolver.StoreImpulses();
// Integrate positions
for (int i = 0; i < BodyCount; ++i)
{
FPVector2 c = _positions[i].c;
FP a = _positions[i].a;
FPVector2 v = _velocities[i].v;
FP w = _velocities[i].w;
// Check for large velocities
FPVector2 translation = h * v;
if (FPVector2.Dot(translation, translation) > Settings.MaxTranslationSquared)
{
FP ratio = Settings.MaxTranslation / translation.magnitude;
v *= ratio;
}
FP rotation = h * w;
if (rotation * rotation > Settings.MaxRotationSquared)
{
FP ratio = Settings.MaxRotation / FP.Abs(rotation);
w *= ratio;
}
// Integrate
c += h * v;
a += h * w;
_positions[i].c = c;
_positions[i].a = a;
_velocities[i].v = v;
_velocities[i].w = w;
}
// Solve position constraints
bool positionSolved = false;
for (int i = 0; i < Settings.PositionIterations; ++i)
{
bool contactsOkay = _contactSolver.SolvePositionConstraints();
bool jointsOkay = true;
for (int j = 0; j < JointCount; ++j)
{
Joint2D joint = _joints[j];
if (!joint.Enabled)
{
continue;
}
bool jointOkay = joint.SolvePositionConstraints(ref solverData);
jointsOkay = jointsOkay && jointOkay;
}
if (contactsOkay && jointsOkay)
{
// Exit early if the position errors are small.
positionSolved = true;
break;
}
}
// Copy state buffers back to the bodies
for (int i = 0; i < BodyCount; ++i)
{
Body body = Bodies[i];
body._sweep.C = _positions[i].c;
body._sweep.A = _positions[i].a;
body._linearVelocity = _velocities[i].v;
body._angularVelocity = _velocities[i].w;
body.SynchronizeTransform();
}
Report(_contactSolver._velocityConstraints);
if (Settings.AllowSleep)
{
FP minSleepTime = Settings.MaxFP;
for (int i = 0; i < BodyCount; ++i)
{
Body b = Bodies[i];
if (b.BodyType == BodyType.Static)
{
continue;
}
if (!b.SleepingAllowed || b._angularVelocity * b._angularVelocity > AngTolSqr || FPVector2.Dot(b._linearVelocity, b._linearVelocity) > LinTolSqr)
{
b._sleepTime = 0.0f;
minSleepTime = 0.0f;
}
else
{
b._sleepTime += h;
minSleepTime = Spax.FPMath.Min(minSleepTime, b._sleepTime);
}
}
if (minSleepTime >= Settings.TimeToSleep && positionSolved)
{
for (int i = 0; i < BodyCount; ++i)
{
Body b = Bodies[i];
b.Awake = false;
}
}
}
}
/// <summary>
/// Requires two existing revolute or prismatic joints (any combination will work).
/// The provided joints must attach a dynamic body to a static body.
/// </summary>
/// <param name="jointA">The first joint.</param>
/// <param name="jointB">The second joint.</param>
/// <param name="ratio">The ratio.</param>
/// <param name="bodyA">The first body</param>
/// <param name="bodyB">The second body</param>
// FP - public GearJoint(Body bodyA, Body bodyB, Joint jointA, Joint jointB, FP ratio = 1f)
public GearJoint(Body bodyA, Body bodyB, Joint2D jointA, Joint2D jointB, FP ratio)
{
JointType = JointType.Gear;
BodyA = bodyA;
BodyB = bodyB;
JointA = jointA;
JointB = jointB;
Ratio = ratio;
_typeA = jointA.JointType;
_typeB = jointB.JointType;
Debug.Assert(_typeA == JointType.Revolute || _typeA == JointType.Prismatic || _typeA == JointType.FixedRevolute || _typeA == JointType.FixedPrismatic);
Debug.Assert(_typeB == JointType.Revolute || _typeB == JointType.Prismatic || _typeB == JointType.FixedRevolute || _typeB == JointType.FixedPrismatic);
FP coordinateA, coordinateB;
// TODO_ERIN there might be some problem with the joint edges in b2Joint.
_bodyC = JointA.BodyA;
_bodyA = JointA.BodyB;
// Get geometry of joint1
Transform xfA = _bodyA._xf;
FP aA = _bodyA._sweep.A;
Transform xfC = _bodyC._xf;
FP aC = _bodyC._sweep.A;
if (_typeA == JointType.Revolute)
{
RevoluteJoint revolute = (RevoluteJoint)jointA;
_localAnchorC = revolute.LocalAnchorA;
_localAnchorA = revolute.LocalAnchorB;
_referenceAngleA = revolute.ReferenceAngle;
_localAxisC = FPVector2.zero;
coordinateA = aA - aC - _referenceAngleA;
}
else
{
PrismaticJoint prismatic = (PrismaticJoint)jointA;
_localAnchorC = prismatic.LocalAnchorA;
_localAnchorA = prismatic.LocalAnchorB;
_referenceAngleA = prismatic.ReferenceAngle;
_localAxisC = prismatic.LocalXAxis;
FPVector2 pC = _localAnchorC;
FPVector2 pA = MathUtils.MulT(xfC.q, MathUtils.Mul(xfA.q, _localAnchorA) + (xfA.p - xfC.p));
coordinateA = FPVector2.Dot(pA - pC, _localAxisC);
}
_bodyD = JointB.BodyA;
_bodyB = JointB.BodyB;
// Get geometry of joint2
Transform xfB = _bodyB._xf;
FP aB = _bodyB._sweep.A;
Transform xfD = _bodyD._xf;
FP aD = _bodyD._sweep.A;
if (_typeB == JointType.Revolute)
{
RevoluteJoint revolute = (RevoluteJoint)jointB;
_localAnchorD = revolute.LocalAnchorA;
_localAnchorB = revolute.LocalAnchorB;
_referenceAngleB = revolute.ReferenceAngle;
_localAxisD = FPVector2.zero;
coordinateB = aB - aD - _referenceAngleB;
}
else
{
PrismaticJoint prismatic = (PrismaticJoint)jointB;
_localAnchorD = prismatic.LocalAnchorA;
_localAnchorB = prismatic.LocalAnchorB;
_referenceAngleB = prismatic.ReferenceAngle;
_localAxisD = prismatic.LocalXAxis;
FPVector2 pD = _localAnchorD;
FPVector2 pB = MathUtils.MulT(xfD.q, MathUtils.Mul(xfB.q, _localAnchorB) + (xfB.p - xfD.p));
coordinateB = FPVector2.Dot(pB - pD, _localAxisD);
}
_ratio = ratio;
_constant = coordinateA + _ratio * coordinateB;
_impulse = 0.0f;
}
public void Add(Joint2D joint)
{
Debug.Assert(JointCount < JointCapacity);
_joints[JointCount++] = joint;
}