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#include "Arbiter.h"
#include "World.h"
#include "Body.h"
#include "Joint.h"
#include "Constants.h"
using namespace Phy2D;
Arbiter::Arbiter(Body* b1, Body* b2)
{
if (b1 < b2)
{
body1 = b1;
body2 = b2;
}
else
{
body1 = b2;
body2 = b1;
}
numContacts = Collide(contacts, body1, body2);
friction = SQRT(body1->friction * body2->friction);
}
void Arbiter::Update(Contact* newContacts, int numNewContacts)
{
Contact mergedContacts[2];
for (int i = 0; i < numNewContacts; ++i)
{
Contact* cNew = newContacts + i;
int k = -1;
for (int j = 0; j < numContacts; ++j)
{
Contact* cOld = contacts + j;
if (cNew->feature.value == cOld->feature.value)
{
k = j;
break;
}
}
if (k > -1)
{
Contact* c = mergedContacts + i;
Contact* cOld = contacts + k;
*c = *cNew;
if (World::warmStarting)
{
c->Pn = cOld->Pn;
c->Pt = cOld->Pt;
c->Pnb = cOld->Pnb;
}
else
{
c->Pn = _0;
c->Pt = _0;
c->Pnb = _0;
}
}
else
{
mergedContacts[i] = newContacts[i];
}
}
for (int i = 0; i < numNewContacts; ++i)
contacts[i] = mergedContacts[i];
numContacts = numNewContacts;
}
void Arbiter::PreStep(fixed inv_dt)
{
const fixed k_allowedPenetration = _0_01;
fixed k_biasFactor = World::positionCorrection ? _0_2 : _0;
for (int i = 0; i < numContacts; ++i)
{
Contact* c = contacts + i;
Vec2 r1 = c->position - body1->position;
Vec2 r2 = c->position - body2->position;
// Precompute normal mass, tangent mass, and bias.
fixed rn1 = Dot(r1, c->normal);
fixed rn2 = Dot(r2, c->normal);
fixed kNormal = body1->invMass + body2->invMass;
kNormal += body1->invI * (Dot(r1, r1) - rn1 * rn1) + body2->invI * (Dot(r2, r2) - rn2 * rn2);
c->massNormal = (fixed)_1 / kNormal;
Vec2 tangent = Cross(c->normal, _1);
fixed rt1 = Dot(r1, tangent);
fixed rt2 = Dot(r2, tangent);
fixed kTangent = body1->invMass + body2->invMass;
kTangent += body1->invI * (Dot(r1, r1) - rt1 * rt1) + body2->invI * (Dot(r2, r2) - rt2 * rt2);
c->massTangent = (fixed)_1 / kTangent;
c->bias = -k_biasFactor * inv_dt * Min(_0, c->separation + k_allowedPenetration);
if (World::accumulateImpulses)
{
// Apply normal + friction impulse
Vec2 P = c->Pn * c->normal + c->Pt * tangent;
body1->velocity -= body1->invMass * P;
body1->angularVelocity -= body1->invI * Cross(r1, P);
body2->velocity += body2->invMass * P;
body2->angularVelocity += body2->invI * Cross(r2, P);
}
}
}
void Arbiter::ApplyImpulse()
{
Body* b1 = body1;
Body* b2 = body2;
for (int i = 0; i < numContacts; ++i)
{
Contact* c = contacts + i;
c->r1 = c->position - b1->position;
c->r2 = c->position - b2->position;
// Relative velocity at contact
Vec2 dv = b2->velocity + Cross(b2->angularVelocity, c->r2) - b1->velocity - Cross(b1->angularVelocity, c->r1);
// Compute normal impulse
fixed vn = Dot(dv, c->normal);
fixed dPn = c->massNormal * (-vn + c->bias);
if (World::accumulateImpulses)
{
// Clamp the accumulated impulse
fixed Pn0 = c->Pn;
c->Pn = Max(Pn0 + dPn, _0);
dPn = c->Pn - Pn0;
}
else
{
dPn = Max(dPn, _0);
}
// Apply contact impulse
Vec2 Pn = dPn * c->normal;
b1->velocity -= b1->invMass * Pn;
b1->angularVelocity -= b1->invI * Cross(c->r1, Pn);
b2->velocity += b2->invMass * Pn;
b2->angularVelocity += b2->invI * Cross(c->r2, Pn);
// Relative velocity at contact
dv = b2->velocity + Cross(b2->angularVelocity, c->r2) - b1->velocity - Cross(b1->angularVelocity, c->r1);
Vec2 tangent = Cross(c->normal, _1);
fixed vt = Dot(dv, tangent);
fixed dPt = c->massTangent * (-vt);
if (World::accumulateImpulses)
{
// Compute friction impulse
fixed maxPt = friction * c->Pn;
// Clamp friction
fixed oldTangentImpulse = c->Pt;
c->Pt = Clamp(oldTangentImpulse + dPt, -maxPt, maxPt);
dPt = c->Pt - oldTangentImpulse;
}
else
{
fixed maxPt = friction * dPn;
dPt = Clamp(dPt, -maxPt, maxPt);
}
// Apply contact impulse
Vec2 Pt = dPt * tangent;
b1->velocity -= b1->invMass * Pt;
b1->angularVelocity -= b1->invI * Cross(c->r1, Pt);
b2->velocity += b2->invMass * Pt;
b2->angularVelocity += b2->invI * Cross(c->r2, Pt);
}
}
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