public void Reset(Contact[] contacts, int contactCount, float impulseRatio)
{
_contacts = contacts;
_constraintCount = contactCount;
// grow the array
if (_constraints == null || _constraints.Length < _constraintCount)
{
_constraints = new ContactConstraint[_constraintCount * 2];
}
for (int i = 0; i < _constraintCount; ++i)
{
Contact contact = contacts[i];
Fixture fixtureA = contact._fixtureA;
Fixture fixtureB = contact._fixtureB;
Shape shapeA = fixtureA.GetShape();
Shape shapeB = fixtureB.GetShape();
float radiusA = shapeA._radius;
float radiusB = shapeB._radius;
Body bodyA = fixtureA.GetBody();
Body bodyB = fixtureB.GetBody();
Manifold manifold;
contact.GetManifold(out manifold);
float friction = Settings.b2MixFriction(fixtureA.GetFriction(), fixtureB.GetFriction());
float restitution = Settings.b2MixRestitution(fixtureA.GetRestitution(), fixtureB.GetRestitution());
Vector2 vA = bodyA._linearVelocity;
Vector2 vB = bodyB._linearVelocity;
float wA = bodyA._angularVelocity;
float wB = bodyB._angularVelocity;
Debug.Assert(manifold._pointCount > 0);
WorldManifold worldManifold = new WorldManifold(ref manifold, ref bodyA._xf, radiusA, ref bodyB._xf, radiusB);
ContactConstraint cc = _constraints[i];
cc.bodyA = bodyA;
cc.bodyB = bodyB;
cc.manifold = manifold;
cc.normal = worldManifold._normal;
cc.pointCount = manifold._pointCount;
cc.friction = friction;
cc.localNormal = manifold._localNormal;
cc.localPoint = manifold._localPoint;
cc.radius = radiusA + radiusB;
cc.type = manifold._type;
for (int j = 0; j < cc.pointCount; ++j)
{
ManifoldPoint cp = manifold._points[j];
ContactConstraintPoint ccp = cc.points[j];
ccp.normalImpulse = impulseRatio * cp.NormalImpulse;
ccp.tangentImpulse = impulseRatio * cp.TangentImpulse;
ccp.localPoint = cp.LocalPoint;
ccp.rA = worldManifold._points[j] - bodyA._sweep.c;
ccp.rB = worldManifold._points[j] - bodyB._sweep.c;
#if MATH_OVERLOADS
float rnA = MathUtils.Cross(ccp.rA, cc.normal);
float rnB = MathUtils.Cross(ccp.rB, cc.normal);
#else
float rnA = ccp.rA.X * cc.normal.Y - ccp.rA.Y * cc.normal.X;
float rnB = ccp.rB.X * cc.normal.Y - ccp.rB.Y * cc.normal.X;
#endif
rnA *= rnA;
rnB *= rnB;
float kNormal = bodyA._invMass + bodyB._invMass + bodyA._invI * rnA + bodyB._invI * rnB;
Debug.Assert(kNormal > Settings.b2_epsilon);
ccp.normalMass = 1.0f / kNormal;
#if MATH_OVERLOADS
Vector2 tangent = MathUtils.Cross(cc.normal, 1.0f);
float rtA = MathUtils.Cross(ccp.rA, tangent);
float rtB = MathUtils.Cross(ccp.rB, tangent);
#else
Vector2 tangent = new Vector2(cc.normal.Y, -cc.normal.X);
float rtA = ccp.rA.X * tangent.Y - ccp.rA.Y * tangent.X;
float rtB = ccp.rB.X * tangent.Y - ccp.rB.Y * tangent.X;
#endif
rtA *= rtA;
rtB *= rtB;
float kTangent = bodyA._invMass + bodyB._invMass + bodyA._invI * rtA + bodyB._invI * rtB;
Debug.Assert(kTangent > Settings.b2_epsilon);
ccp.tangentMass = 1.0f / kTangent;
// Setup a velocity bias for restitution.
ccp.velocityBias = 0.0f;
float vRel = Vector2.Dot(cc.normal, vB + MathUtils.Cross(wB, ccp.rB) - vA - MathUtils.Cross(wA, ccp.rA));
if (vRel < -Settings.b2_velocityThreshold)
{
ccp.velocityBias = -restitution * vRel;
}
cc.points[j] = ccp;
}
// If we have two points, then prepare the block solver.
if (cc.pointCount == 2)
{
ContactConstraintPoint ccp1 = cc.points[0];
ContactConstraintPoint ccp2 = cc.points[1];
float invMassA = bodyA._invMass;
float invIA = bodyA._invI;
float invMassB = bodyB._invMass;
float invIB = bodyB._invI;
float rn1A = MathUtils.Cross(ccp1.rA, cc.normal);
float rn1B = MathUtils.Cross(ccp1.rB, cc.normal);
float rn2A = MathUtils.Cross(ccp2.rA, cc.normal);
float rn2B = MathUtils.Cross(ccp2.rB, cc.normal);
float k11 = invMassA + invMassB + invIA * rn1A * rn1A + invIB * rn1B * rn1B;
float k22 = invMassA + invMassB + invIA * rn2A * rn2A + invIB * rn2B * rn2B;
float k12 = invMassA + invMassB + invIA * rn1A * rn2A + invIB * rn1B * rn2B;
// Ensure a reasonable condition number.
const float k_maxConditionNumber = 100.0f;
if (k11 * k11 < k_maxConditionNumber * (k11 * k22 - k12 * k12))
{
// K is safe to invert.
cc.K = new Mat22(new Vector2(k11, k12), new Vector2(k12, k22));
cc.normalMass = cc.K.GetInverse();
}
else
{
// The constraints are redundant, just use one.
// TODO_ERIN use deepest?
cc.pointCount = 1;
}
}
_constraints[i] = cc;
}
}