internal override void InitVelocityConstraints(TimeStep step)
{
Body b = _body2;
float mass = b.GetMass();
// Frequency
float omega = 2.0f * Settings.Pi * _frequencyHz;
// Damping coefficient
float d = 2.0f * mass * _dampingRatio * omega;
// Spring stiffness
float k = mass * (omega * omega);
// magic formulas
// gamma has units of inverse mass.
// beta has units of inverse time.
Box2DXDebug.Assert(d + step.Dt * k > Settings.FLT_EPSILON);
_gamma = 1.0f / (step.Dt * (d + step.Dt * k));
_beta = step.Dt * k * _gamma;
// Compute the effective mass matrix.
Vector2 r = b.GetTransform().TransformDirection(_localAnchor - b.GetLocalCenter());
// K = [(1/m1 + 1/m2) * eye(2) - skew(r1) * invI1 * skew(r1) - skew(r2) * invI2 * skew(r2)]
// = [1/m1+1/m2 0 ] + invI1 * [r1.y*r1.y -r1.x*r1.y] + invI2 * [r1.y*r1.y -r1.x*r1.y]
// [ 0 1/m1+1/m2] [-r1.x*r1.y r1.x*r1.x] [-r1.x*r1.y r1.x*r1.x]
float invMass = b._invMass;
float invI = b._invI;
Mat22 K1 = new Mat22();
K1.Col1.X = invMass; K1.Col2.X = 0.0f;
K1.Col1.Y = 0.0f; K1.Col2.Y = invMass;
Mat22 K2 = new Mat22();
K2.Col1.X = invI * r.Y * r.Y; K2.Col2.X = -invI * r.X * r.Y;
K2.Col1.Y = -invI * r.X * r.Y; K2.Col2.Y = invI * r.X * r.X;
Mat22 K = K1 + K2;
K.Col1.X += _gamma;
K.Col2.Y += _gamma;
_mass = K.GetInverse();
_C = b._sweep.C + r - _target;
// Cheat with some damping
b._angularVelocity *= 0.98f;
// Warm starting.
_impulse *= step.DtRatio;
b._linearVelocity += invMass * _impulse;
b._angularVelocity += invI * r.Cross(_impulse);
}
internal override void InitVelocityConstraints(TimeStep step)
{
Body body = this._body2;
float mass = body.GetMass();
float num = 2f * Settings.Pi * this._frequencyHz;
float num2 = 2f * mass * this._dampingRatio * num;
float num3 = mass * (num * num);
Box2DXDebug.Assert(num2 + step.Dt * num3 > Settings.FLT_EPSILON);
this._gamma = 1f / (step.Dt * (num2 + step.Dt * num3));
this._beta = step.Dt * num3 * this._gamma;
Vec2 vec = Box2DX.Common.Math.Mul(body.GetXForm().R, this._localAnchor - body.GetLocalCenter());
float invMass = body._invMass;
float invI = body._invI;
Mat22 a = default(Mat22);
a.Col1.X = invMass;
a.Col2.X = 0f;
a.Col1.Y = 0f;
a.Col2.Y = invMass;
Mat22 b = default(Mat22);
b.Col1.X = invI * vec.Y * vec.Y;
b.Col2.X = -invI * vec.X * vec.Y;
b.Col1.Y = -invI * vec.X * vec.Y;
b.Col2.Y = invI * vec.X * vec.X;
Mat22 mat = a + b;
mat.Col1.X = mat.Col1.X + this._gamma;
mat.Col2.Y = mat.Col2.Y + this._gamma;
this._mass = mat.Invert();
this._C = body._sweep.C + vec - this._target;
body._angularVelocity *= 0.98f;
this._impulse *= step.DtRatio;
Body expr_21D = body;
expr_21D._linearVelocity += invMass * this._impulse;
body._angularVelocity += invI * Vec2.Cross(vec, this._impulse);
}
