public void Reset(TimeStep step, int count, Contact[] contacts, Position[] positions, Velocity[] velocities)
{
_step = step;
_count = count;
_positions = positions;
_velocities = velocities;
_contacts = contacts;
// grow the array
if (VelocityConstraints == null || VelocityConstraints.Length < count)
{
VelocityConstraints = new ContactVelocityConstraint[count * 2];
_positionConstraints = new ContactPositionConstraint[count * 2];
for (int i = 0; i < VelocityConstraints.Length; i++)
{
VelocityConstraints[i] = new ContactVelocityConstraint();
}
for (int i = 0; i < _positionConstraints.Length; i++)
{
_positionConstraints[i] = new ContactPositionConstraint();
}
}
// Initialize position independent portions of the constraints.
for (int i = 0; i < _count; ++i)
{
Contact contact = contacts[i];
Fixture fixtureA = contact.FixtureA;
Fixture fixtureB = contact.FixtureB;
Shape shapeA = fixtureA.Shape;
Shape shapeB = fixtureB.Shape;
float radiusA = shapeA.Radius;
float radiusB = shapeB.Radius;
Body bodyA = fixtureA.Body;
Body bodyB = fixtureB.Body;
Manifold manifold = contact.Manifold;
int pointCount = manifold.PointCount;
System.Diagnostics.Debug.Assert(pointCount > 0);
ContactVelocityConstraint vc = VelocityConstraints[i];
vc.Friction = contact.Friction;
vc.Restitution = contact.Restitution;
vc.TangentSpeed = contact.TangentSpeed;
vc.IndexA = bodyA.IslandIndex;
vc.IndexB = bodyB.IslandIndex;
vc.InvMassA = bodyA._invMass;
vc.InvMassB = bodyB._invMass;
vc.InvIA = bodyA._invI;
vc.InvIB = bodyB._invI;
vc.ContactIndex = i;
vc.PointCount = pointCount;
vc.K.SetZero();
vc.NormalMass.SetZero();
ContactPositionConstraint pc = _positionConstraints[i];
pc.IndexA = bodyA.IslandIndex;
pc.IndexB = bodyB.IslandIndex;
pc.InvMassA = bodyA._invMass;
pc.InvMassB = bodyB._invMass;
pc.LocalCenterA = bodyA._sweep.LocalCenter;
pc.LocalCenterB = bodyB._sweep.LocalCenter;
pc.InvIA = bodyA._invI;
pc.InvIB = bodyB._invI;
pc.LocalNormal = manifold.LocalNormal;
pc.LocalPoint = manifold.LocalPoint;
pc.PointCount = pointCount;
pc.RadiusA = radiusA;
pc.RadiusB = radiusB;
pc.Type = manifold.Type;
for (int j = 0; j < pointCount; ++j)
{
ManifoldPoint cp = manifold.Points[j];
VelocityConstraintPoint vcp = vc.Points[j];
if (Settings.EnableWarmstarting)
{
vcp.NormalImpulse = _step.dtRatio * cp.NormalImpulse;
vcp.TangentImpulse = _step.dtRatio * cp.TangentImpulse;
}
else
{
vcp.NormalImpulse = 0.0f;
vcp.TangentImpulse = 0.0f;
}
vcp.rA = Vector2.Zero;
vcp.rB = Vector2.Zero;
vcp.NormalMass = 0.0f;
vcp.TangentMass = 0.0f;
vcp.VelocityBias = 0.0f;
pc.LocalPoints[j] = cp.LocalPoint;
}
}
}
// Sequential position solver for position constraints.
public bool SolveTOIPositionConstraints(int toiIndexA, int toiIndexB)
{
float minSeparation = 0.0f;
for (int i = 0; i < _count; ++i)
{
ContactPositionConstraint pc = _positionConstraints[i];
int indexA = pc.IndexA;
int indexB = pc.IndexB;
Vector2 localCenterA = pc.LocalCenterA;
Vector2 localCenterB = pc.LocalCenterB;
int pointCount = pc.PointCount;
float mA = 0.0f;
float iA = 0.0f;
if (indexA == toiIndexA || indexA == toiIndexB)
{
mA = pc.InvMassA;
iA = pc.InvIA;
}
float mB = 0.0f;
float iB = 0.0f;
if (indexB == toiIndexA || indexB == toiIndexB)
{
mB = pc.InvMassB;
iB = pc.InvIB;
}
Vector2 cA = _positions[indexA].C;
float aA = _positions[indexA].A;
Vector2 cB = _positions[indexB].C;
float aB = _positions[indexB].A;
// Solve normal constraints
for (int j = 0; j < pointCount; ++j)
{
Transform xfA = new Transform();
Transform xfB = new Transform();
xfA.q.Set(aA);
xfB.q.Set(aB);
xfA.p = cA - MathUtils.Mul(xfA.q, localCenterA);
xfB.p = cB - MathUtils.Mul(xfB.q, localCenterB);
PositionSolverManifold.Initialize(pc, xfA, xfB, j, out Vector2 normal, out Vector2 point, out float separation);
Vector2 rA = point - cA;
Vector2 rB = point - cB;
// Track max constraint error.
minSeparation = Math.Min(minSeparation, separation);
// Prevent large corrections and allow slop.
float C = MathUtils.Clamp(Settings.Baumgarte * (separation + Settings.LinearSlop), -Settings.MaxLinearCorrection, 0.0f);
// Compute the effective mass.
float rnA = MathUtils.Cross(rA, normal);
float rnB = MathUtils.Cross(rB, normal);
float K = mA + mB + iA * rnA * rnA + iB * rnB * rnB;
// Compute normal impulse
float impulse = K > 0.0f ? -C / K : 0.0f;
Vector2 P = impulse * normal;
cA -= mA * P;
aA -= iA * MathUtils.Cross(rA, P);
cB += mB * P;
aB += iB * MathUtils.Cross(rB, P);
}
_positions[indexA].C = cA;
_positions[indexA].A = aA;
_positions[indexB].C = cB;
_positions[indexB].A = aB;
}
// We can't expect minSpeparation >= -b2_linearSlop because we don't
// push the separation above -b2_linearSlop.
return(minSeparation >= -1.5f * Settings.LinearSlop);
}
/// <summary>
/// Initialize position dependent portions of the velocity constraints.
/// </summary>
public void InitializeVelocityConstraints()
{
for (int i = 0; i < _count; ++i)
{
ContactVelocityConstraint vc = VelocityConstraints[i];
ContactPositionConstraint pc = _positionConstraints[i];
float radiusA = pc.RadiusA;
float radiusB = pc.RadiusB;
Manifold manifold = _contacts[vc.ContactIndex].Manifold;
int indexA = vc.IndexA;
int indexB = vc.IndexB;
float mA = vc.InvMassA;
float mB = vc.InvMassB;
float iA = vc.InvIA;
float iB = vc.InvIB;
Vector2 localCenterA = pc.LocalCenterA;
Vector2 localCenterB = pc.LocalCenterB;
Vector2 cA = _positions[indexA].C;
float aA = _positions[indexA].A;
Vector2 vA = _velocities[indexA].V;
float wA = _velocities[indexA].W;
Vector2 cB = _positions[indexB].C;
float aB = _positions[indexB].A;
Vector2 vB = _velocities[indexB].V;
float wB = _velocities[indexB].W;
System.Diagnostics.Debug.Assert(manifold.PointCount > 0);
Transform xfA = new Transform();
Transform xfB = new Transform();
xfA.q.Set(aA);
xfB.q.Set(aB);
xfA.p = cA - MathUtils.Mul(xfA.q, localCenterA);
xfB.p = cB - MathUtils.Mul(xfB.q, localCenterB);
WorldManifold.Initialize(ref manifold, ref xfA, radiusA, ref xfB, radiusB, out Vector2 normal, out FixedArray2 <Vector2> points, out _);
vc.Normal = normal;
int pointCount = vc.PointCount;
for (int j = 0; j < pointCount; ++j)
{
VelocityConstraintPoint vcp = vc.Points[j];
vcp.rA = points[j] - cA;
vcp.rB = points[j] - cB;
float rnA = MathUtils.Cross(vcp.rA, vc.Normal);
float rnB = MathUtils.Cross(vcp.rB, vc.Normal);
float kNormal = mA + mB + iA * rnA * rnA + iB * rnB * rnB;
vcp.NormalMass = kNormal > 0.0f ? 1.0f / kNormal : 0.0f;
Vector2 tangent = MathUtils.Cross(vc.Normal, 1.0f);
float rtA = MathUtils.Cross(vcp.rA, tangent);
float rtB = MathUtils.Cross(vcp.rB, tangent);
float kTangent = mA + mB + iA * rtA * rtA + iB * rtB * rtB;
vcp.TangentMass = kTangent > 0.0f ? 1.0f / kTangent : 0.0f;
// Setup a velocity bias for restitution.
vcp.VelocityBias = 0.0f;
float vRel = Vector2.Dot(vc.Normal, vB + MathUtils.Cross(wB, vcp.rB) - vA - MathUtils.Cross(wA, vcp.rA));
if (vRel < -Settings.VelocityThreshold)
{
vcp.VelocityBias = -vc.Restitution * vRel;
}
}
// If we have two points, then prepare the block solver.
if (vc.PointCount == 2 && Settings.BlockSolve)
{
VelocityConstraintPoint vcp1 = vc.Points[0];
VelocityConstraintPoint vcp2 = vc.Points[1];
float rn1A = MathUtils.Cross(vcp1.rA, vc.Normal);
float rn1B = MathUtils.Cross(vcp1.rB, vc.Normal);
float rn2A = MathUtils.Cross(vcp2.rA, vc.Normal);
float rn2B = MathUtils.Cross(vcp2.rB, vc.Normal);
float k11 = mA + mB + iA * rn1A * rn1A + iB * rn1B * rn1B;
float k22 = mA + mB + iA * rn2A * rn2A + iB * rn2B * rn2B;
float k12 = mA + mB + iA * rn1A * rn2A + iB * rn1B * rn2B;
// Ensure a reasonable condition number.
const float k_maxConditionNumber = 1000.0f;
if (k11 * k11 < k_maxConditionNumber * (k11 * k22 - k12 * k12))
{
// K is safe to invert.
vc.K.ex = new Vector2(k11, k12);
vc.K.ey = new Vector2(k12, k22);
vc.NormalMass = vc.K.Inverse;
}
else
{
// The constraints are redundant, just use one.
// TODO_ERIN use deepest?
vc.PointCount = 1;
}
}
}
}