/// <summary>
/// Describes whether this instance synchronize fixtures
/// </summary>
/// <returns>The bool</returns>
internal bool SynchronizeFixtures()
{
XForm xf1 = new XForm();
xf1.R.Set(Sweep.A0);
xf1.Position = Sweep.C0 - Math.Mul(xf1.R, Sweep.LocalCenter);
bool inRange = true;
for (Fixture f = FixtureList; f != null; f = f.Next)
{
inRange = f.Synchronize(world.BroadPhase, xf1, Xf);
if (inRange == false)
{
break;
}
}
if (inRange == false)
{
Flags |= BodyFlags.Frozen;
LinearVelocity.SetZero();
AngularVelocity = 0.0f;
// Failure
return(false);
}
// Success
return(true);
}
// TODO_ERIN adjust linear velocity and torque to account for movement of center.
/// <summary>
/// Set the mass properties. Note that this changes the center of mass position.
/// If you are not sure how to compute mass properties, use SetMassFromShapes.
/// The inertia tensor is assumed to be relative to the center of mass.
/// </summary>
/// <param name="massData">The mass properties.</param>
public void SetMass(MassData massData)
{
Box2DxDebug.Assert(world.Lock == false);
if (world.Lock)
{
return;
}
InvMass = 0.0f;
I = 0.0f;
InvI = 0.0f;
Mass = massData.Mass;
if (Mass > 0.0f)
{
InvMass = 1.0f / Mass;
}
I = massData.I;
if (I > 0.0f && (Flags & BodyFlags.FixedRotation) == 0)
{
InvI = 1.0f / I;
}
// Move center of mass.
Sweep.LocalCenter = massData.Center;
Sweep.C0 = Sweep.C = Math.Mul(Xf, Sweep.LocalCenter);
BodyType oldType = type;
if (InvMass == 0.0f && InvI == 0.0f)
{
type = BodyType.Static;
}
else
{
type = BodyType.Dynamic;
}
// If the body type changed, we need to refilter the broad-phase proxies.
if (oldType != type)
{
for (Fixture f = FixtureList; f != null; f = f.Next)
{
f.RefilterProxy(world.BroadPhase, Xf);
}
}
}
/// <summary>
/// Set the position of the body's origin and rotation (radians).
/// This breaks any contacts and wakes the other bodies.
/// </summary>
/// <param name="position">
/// The new world position of the body's origin (not necessarily
/// the center of mass).
/// </param>
/// <param name="angle">The new world rotation angle of the body in radians.</param>
/// <returns>
/// Return false if the movement put a shape outside the world. In this case the
/// body is automatically frozen.
/// </returns>
public bool SetXForm(Vec2 position, float angle)
{
Box2DxDebug.Assert(world.Lock == false);
if (world.Lock)
{
return(true);
}
if (IsFrozen())
{
return(false);
}
Xf.R.Set(angle);
Xf.Position = position;
Sweep.C0 = Sweep.C = Math.Mul(Xf, Sweep.LocalCenter);
Sweep.A0 = Sweep.A = angle;
bool freeze = false;
for (Fixture f = FixtureList; f != null; f = f.Next)
{
bool inRange = f.Synchronize(world.BroadPhase, Xf, Xf);
if (inRange == false)
{
freeze = true;
break;
}
}
if (freeze)
{
Flags |= BodyFlags.Frozen;
LinearVelocity.SetZero();
AngularVelocity = 0.0f;
// Failure
return(false);
}
// Success
world.BroadPhase.Commit();
return(true);
}
/// <summary>
/// Get the world coordinates of a vector given the local coordinates.
/// </summary>
/// <param name="localVector">A vector fixed in the body.</param>
/// <returns>Return the same vector expressed in world coordinates.</returns>
public Vec2 GetWorldVector(Vec2 localVector)
{
return(Math.Mul(Xf.R, localVector));
}
/// <summary>
/// Get the world coordinates of a point given the local coordinates.
/// </summary>
/// <param name="localPoint">A point on the body measured relative the the body's origin.</param>
/// <returns>Return the same point expressed in world coordinates.</returns>
public Vec2 GetWorldPoint(Vec2 localPoint)
{
return(Math.Mul(Xf, localPoint));
}
// TODO_ERIN adjust linear velocity and torque to account for movement of center.
/// <summary>
/// Compute the mass properties from the attached shapes. You typically call this
/// after adding all the shapes. If you add or remove shapes later, you may want
/// to call this again. Note that this changes the center of mass position.
/// </summary>
public void SetMassFromShapes()
{
Box2DxDebug.Assert(world.Lock == false);
if (world.Lock)
{
return;
}
// Compute mass data from shapes. Each shape has its own density.
Mass = 0.0f;
InvMass = 0.0f;
I = 0.0f;
InvI = 0.0f;
Vec2 center = Vec2.Zero;
for (Fixture f = FixtureList; f != null; f = f.Next)
{
MassData massData;
f.ComputeMass(out massData);
Mass += massData.Mass;
center += massData.Mass * massData.Center;
I += massData.I;
}
// Compute center of mass, and shift the origin to the COM.
if (Mass > 0.0f)
{
InvMass = 1.0f / Mass;
center *= InvMass;
}
if (I > 0.0f && (Flags & BodyFlags.FixedRotation) == 0)
{
// Center the inertia about the center of mass.
I -= Mass * Vec2.Dot(center, center);
Box2DxDebug.Assert(I > 0.0f);
InvI = 1.0f / I;
}
else
{
I = 0.0f;
InvI = 0.0f;
}
// Move center of mass.
Sweep.LocalCenter = center;
Sweep.C0 = Sweep.C = Math.Mul(Xf, Sweep.LocalCenter);
BodyType oldType = type;
if (InvMass == 0.0f && InvI == 0.0f)
{
type = BodyType.Static;
}
else
{
type = BodyType.Dynamic;
}
// If the body type changed, we need to refilter the broad-phase proxies.
if (oldType != type)
{
for (Fixture f = FixtureList; f != null; f = f.Next)
{
f.RefilterProxy(world.BroadPhase, Xf);
}
}
}
internal XForm Xf; // the body origin transform
/// <summary>
/// Initializes a new instance of the <see cref="Body" /> class
/// </summary>
/// <param name="bd">The bd</param>
/// <param name="world">The world</param>
internal Body(BodyDef bd, World world)
{
Box2DxDebug.Assert(world.Lock == false);
Flags = 0;
if (bd.IsBullet)
{
Flags |= BodyFlags.Bullet;
}
if (bd.FixedRotation)
{
Flags |= BodyFlags.FixedRotation;
}
if (bd.AllowSleep)
{
Flags |= BodyFlags.AllowSleep;
}
if (bd.IsSleeping)
{
Flags |= BodyFlags.Sleep;
}
this.world = world;
Xf.Position = bd.Position;
Xf.R.Set(bd.Angle);
Sweep.LocalCenter = bd.MassData.Center;
Sweep.T0 = 1.0f;
Sweep.A0 = Sweep.A = bd.Angle;
Sweep.C0 = Sweep.C = Math.Mul(Xf, Sweep.LocalCenter);
//_jointList = null;
//_contactList = null;
//_controllerList = null;
//_prev = null;
//_next = null;
LinearVelocity = bd.LinearVelocity;
AngularVelocity = bd.AngularVelocity;
LinearDamping = bd.LinearDamping;
AngularDamping = bd.AngularDamping;
//_force.Set(0.0f, 0.0f);
//_torque = 0.0f;
//_linearVelocity.SetZero();
//_angularVelocity = 0.0f;
//_sleepTime = 0.0f;
//_invMass = 0.0f;
//_I = 0.0f;
//_invI = 0.0f;
Mass = bd.MassData.Mass;
if (Mass > 0.0f)
{
InvMass = 1.0f / Mass;
}
I = bd.MassData.I;
if (I > 0.0f && (Flags & BodyFlags.FixedRotation) == 0)
{
InvI = 1.0f / I;
}
if (InvMass == 0.0f && InvI == 0.0f)
{
type = BodyType.Static;
}
else
{
type = BodyType.Dynamic;
}
userData = bd.UserData;
//_fixtureList = null;
//_fixtureCount = 0;
}
/// <summary>
/// Synchronizes the transform
/// </summary>
internal void SynchronizeTransform()
{
Xf.R.Set(Sweep.A);
Xf.Position = Sweep.C - Math.Mul(Xf.R, Sweep.LocalCenter);
}
/// <summary>
/// Solves the velocity constraints
/// </summary>
public void SolveVelocityConstraints()
{
for (int i = 0; i < ConstraintCount; ++i)
{
ContactConstraint c = Constraints[i];
Body bodyA = c.BodyA;
Body bodyB = c.BodyB;
float wA = bodyA.AngularVelocity;
float wB = bodyB.AngularVelocity;
Vec2 vA = bodyA.LinearVelocity;
Vec2 vB = bodyB.LinearVelocity;
float invMassA = bodyA.InvMass;
float invIa = bodyA.InvI;
float invMassB = bodyB.InvMass;
float invIb = bodyB.InvI;
Vec2 normal = c.Normal;
Vec2 tangent = Vec2.Cross(normal, 1.0f);
float friction = c.Friction;
Box2DxDebug.Assert(c.PointCount == 1 || c.PointCount == 2);
unsafe
{
fixed(ContactConstraintPoint *pointsPtr = c.Points)
{
// Solve tangent constraints
for (int j = 0; j < c.PointCount; ++j)
{
ContactConstraintPoint *ccp = &pointsPtr[j];
// Relative velocity at contact
Vec2 dv = vB + Vec2.Cross(wB, ccp->Rb) - vA - Vec2.Cross(wA, ccp->Ra);
// Compute tangent force
float vt = Vec2.Dot(dv, tangent);
float lambda = ccp->TangentMass * -vt;
// b2Clamp the accumulated force
float maxFriction = friction * ccp->NormalImpulse;
float newImpulse = Math.Clamp(ccp->TangentImpulse + lambda, -maxFriction, maxFriction);
lambda = newImpulse - ccp->TangentImpulse;
// Apply contact impulse
Vec2 p = lambda * tangent;
vA -= invMassA * p;
wA -= invIa * Vec2.Cross(ccp->Ra, p);
vB += invMassB * p;
wB += invIb * Vec2.Cross(ccp->Rb, p);
ccp->TangentImpulse = newImpulse;
}
// Solve normal constraints
if (c.PointCount == 1)
{
ContactConstraintPoint ccp = c.Points[0];
// Relative velocity at contact
Vec2 dv = vB + Vec2.Cross(wB, ccp.Rb) - vA - Vec2.Cross(wA, ccp.Ra);
// Compute normal impulse
float vn = Vec2.Dot(dv, normal);
float lambda = -ccp.NormalMass * (vn - ccp.VelocityBias);
// Clamp the accumulated impulse
float newImpulse = Math.Max(ccp.NormalImpulse + lambda, 0.0f);
lambda = newImpulse - ccp.NormalImpulse;
// Apply contact impulse
Vec2 p = lambda * normal;
vA -= invMassA * p;
wA -= invIa * Vec2.Cross(ccp.Ra, p);
vB += invMassB * p;
wB += invIb * Vec2.Cross(ccp.Rb, p);
ccp.NormalImpulse = newImpulse;
}
else
{
// Block solver developed in collaboration with Dirk Gregorius (back in 01/07 on Box2D_Lite).
// Build the mini LCP for this contact patch
//
// vn = A * x + b, vn >= 0, , vn >= 0, x >= 0 and vn_i * x_i = 0 with i = 1..2
//
// A = J * W * JT and J = ( -n, -r1 x n, n, r2 x n )
// b = vn_0 - velocityBias
//
// The system is solved using the "Total enumeration method" (s. Murty). The complementary constraint vn_i * x_i
// implies that we must have in any solution either vn_i = 0 or x_i = 0. So for the 2D contact problem the cases
// vn1 = 0 and vn2 = 0, x1 = 0 and x2 = 0, x1 = 0 and vn2 = 0, x2 = 0 and vn1 = 0 need to be tested. The first valid
// solution that satisfies the problem is chosen.
//
// In order to account of the accumulated impulse 'a' (because of the iterative nature of the solver which only requires
// that the accumulated impulse is clamped and not the incremental impulse) we change the impulse variable (x_i).
//
// Substitute:
//
// x = x' - a
//
// Plug into above equation:
//
// vn = A * x + b
// = A * (x' - a) + b
// = A * x' + b - A * a
// = A * x' + b'
// b' = b - A * a;
ContactConstraintPoint *cp1 = &pointsPtr[0];
ContactConstraintPoint *cp2 = &pointsPtr[1];
Vec2 a = new Vec2(cp1->NormalImpulse, cp2->NormalImpulse);
Box2DxDebug.Assert(a.X >= 0.0f && a.Y >= 0.0f);
// Relative velocity at contact
Vec2 dv1 = vB + Vec2.Cross(wB, cp1->Rb) - vA - Vec2.Cross(wA, cp1->Ra);
Vec2 dv2 = vB + Vec2.Cross(wB, cp2->Rb) - vA - Vec2.Cross(wA, cp2->Ra);
// Compute normal velocity
float vn1 = Vec2.Dot(dv1, normal);
float vn2 = Vec2.Dot(dv2, normal);
Vec2 b;
b.X = vn1 - cp1->VelocityBias;
b.Y = vn2 - cp2->VelocityBias;
b -= Math.Mul(c.K, a);
//const float k_errorTol = 1e-3f;
//B2_NOT_USED(k_errorTol);
for (;;)
{
//
// Case 1: vn = 0
//
// 0 = A * x' + b'
//
// Solve for x':
//
// x' = - inv(A) * b'
//
Vec2 x = -Math.Mul(c.NormalMass, b);
if (x.X >= 0.0f && x.Y >= 0.0f)
{
// Resubstitute for the incremental impulse
Vec2 d = x - a;
// Apply incremental impulse
Vec2 p1 = d.X * normal;
Vec2 p2 = d.Y * normal;
vA -= invMassA * (p1 + p2);
wA -= invIa * (Vec2.Cross(cp1->Ra, p1) + Vec2.Cross(cp2->Ra, p2));
vB += invMassB * (p1 + p2);
wB += invIb * (Vec2.Cross(cp1->Rb, p1) + Vec2.Cross(cp2->Rb, p2));
// Accumulate
cp1->NormalImpulse = x.X;
cp2->NormalImpulse = x.Y;
#if DEBUG_SOLVER
// Postconditions
dv1 = vB + Vec2.Cross(wB, cp1->RB) - vA - Vec2.Cross(wA, cp1->RA);
dv2 = vB + Vec2.Cross(wB, cp2->RB) - vA - Vec2.Cross(wA, cp2->RA);
// Compute normal velocity
vn1 = Vec2.Dot(dv1, normal);
vn2 = Vec2.Dot(dv2, normal);
Box2DXDebug.Assert(Common.Math.Abs(vn1 - cp1.VelocityBias) < k_errorTol);
Box2DXDebug.Assert(Common.Math.Abs(vn2 - cp2.VelocityBias) < k_errorTol);
#endif
break;
}
//
// Case 2: vn1 = 0 and x2 = 0
//
// 0 = a11 * x1' + a12 * 0 + b1'
// vn2 = a21 * x1' + a22 * 0 + b2'
//
x.X = -cp1->NormalMass * b.X;
x.Y = 0.0f;
/*
* vn1 = 0.0f;
*/
vn2 = c.K.Col1.Y * x.X + b.Y;
if (x.X >= 0.0f && vn2 >= 0.0f)
{
// Resubstitute for the incremental impulse
Vec2 d = x - a;
// Apply incremental impulse
Vec2 p1 = d.X * normal;
Vec2 p2 = d.Y * normal;
vA -= invMassA * (p1 + p2);
wA -= invIa * (Vec2.Cross(cp1->Ra, p1) + Vec2.Cross(cp2->Ra, p2));
vB += invMassB * (p1 + p2);
wB += invIb * (Vec2.Cross(cp1->Rb, p1) + Vec2.Cross(cp2->Rb, p2));
// Accumulate
cp1->NormalImpulse = x.X;
cp2->NormalImpulse = x.Y;
#if DEBUG_SOLVER
// Postconditions
dv1 = vB + Vec2.Cross(wB, cp1->RB) - vA - Vec2.Cross(wA, cp1->RA);
// Compute normal velocity
vn1 = Vec2.Dot(dv1, normal);
Box2DXDebug.Assert(Common.Math.Abs(vn1 - cp1.VelocityBias) < k_errorTol);
#endif
break;
}
//
// Case 3: w2 = 0 and x1 = 0
//
// vn1 = a11 * 0 + a12 * x2' + b1'
// 0 = a21 * 0 + a22 * x2' + b2'
//
x.X = 0.0f;
x.Y = -cp2->NormalMass * b.Y;
vn1 = c.K.Col2.X * x.Y + b.X;
/*
* vn2 = 0.0f;
*/
if (x.Y >= 0.0f && vn1 >= 0.0f)
{
// Resubstitute for the incremental impulse
Vec2 d = x - a;
// Apply incremental impulse
Vec2 p1 = d.X * normal;
Vec2 p2 = d.Y * normal;
vA -= invMassA * (p1 + p2);
wA -= invIa * (Vec2.Cross(cp1->Ra, p1) + Vec2.Cross(cp2->Ra, p2));
vB += invMassB * (p1 + p2);
wB += invIb * (Vec2.Cross(cp1->Rb, p1) + Vec2.Cross(cp2->Rb, p2));
// Accumulate
cp1->NormalImpulse = x.X;
cp2->NormalImpulse = x.Y;
#if DEBUG_SOLVER
// Postconditions
dv2 = vB + Vec2.Cross(wB, cp2->RB) - vA - Vec2.Cross(wA, cp2->RA);
// Compute normal velocity
vn2 = Vec2.Dot(dv2, normal);
Box2DXDebug.Assert(Common.Math.Abs(vn2 - cp2.VelocityBias) < k_errorTol);
#endif
break;
}
//
// Case 4: x1 = 0 and x2 = 0
//
// vn1 = b1
// vn2 = b2;
x.X = 0.0f;
x.Y = 0.0f;
vn1 = b.X;
vn2 = b.Y;
if (vn1 >= 0.0f && vn2 >= 0.0f)
{
// Resubstitute for the incremental impulse
Vec2 d = x - a;
// Apply incremental impulse
Vec2 p1 = d.X * normal;
Vec2 p2 = d.Y * normal;
vA -= invMassA * (p1 + p2);
wA -= invIa * (Vec2.Cross(cp1->Ra, p1) + Vec2.Cross(cp2->Ra, p2));
vB += invMassB * (p1 + p2);
wB += invIb * (Vec2.Cross(cp1->Rb, p1) + Vec2.Cross(cp2->Rb, p2));
// Accumulate
cp1->NormalImpulse = x.X;
cp2->NormalImpulse = x.Y;
}
// No solution, give up. This is hit sometimes, but it doesn't seem to matter.
break;
}
}
bodyA.LinearVelocity = vA;
bodyA.AngularVelocity = wA;
bodyB.LinearVelocity = vB;
bodyB.AngularVelocity = wB;
}
}
}
}