virtualx-engine/thirdparty/bullet/Bullet3Dynamics/shared/b3ConvertConstraint4.h

#include "Bullet3Collision/NarrowPhaseCollision/shared/b3Contact4Data.h"
#include "Bullet3Dynamics/shared/b3ContactConstraint4.h"
#include "Bullet3Collision/NarrowPhaseCollision/shared/b3RigidBodyData.h"


void b3PlaneSpace1 (b3Float4ConstArg n, b3Float4* p, b3Float4* q);
 void b3PlaneSpace1 (b3Float4ConstArg n, b3Float4* p, b3Float4* q)
{
  if (b3Fabs(n.z) > 0.70710678f) {
    // choose p in y-z plane
    float a = n.y*n.y + n.z*n.z;
    float k = 1.f/sqrt(a);
    p[0].x = 0;
	p[0].y = -n.z*k;
	p[0].z = n.y*k;
    // set q = n x p
    q[0].x = a*k;
	q[0].y = -n.x*p[0].z;
	q[0].z = n.x*p[0].y;
  }
  else {
    // choose p in x-y plane
    float a = n.x*n.x + n.y*n.y;
    float k = 1.f/sqrt(a);
    p[0].x = -n.y*k;
	p[0].y = n.x*k;
	p[0].z = 0;
    // set q = n x p
    q[0].x = -n.z*p[0].y;
	q[0].y = n.z*p[0].x;
	q[0].z = a*k;
  }
}


 
void setLinearAndAngular( b3Float4ConstArg n, b3Float4ConstArg r0, b3Float4ConstArg r1, b3Float4* linear, b3Float4* angular0, b3Float4* angular1)
{
	*linear = b3MakeFloat4(n.x,n.y,n.z,0.f);
	*angular0 = b3Cross3(r0, n);
	*angular1 = -b3Cross3(r1, n);
}


float calcRelVel( b3Float4ConstArg l0, b3Float4ConstArg l1, b3Float4ConstArg a0, b3Float4ConstArg a1, b3Float4ConstArg linVel0,
	b3Float4ConstArg angVel0, b3Float4ConstArg linVel1, b3Float4ConstArg angVel1 )
{
	return b3Dot3F4(l0, linVel0) + b3Dot3F4(a0, angVel0) + b3Dot3F4(l1, linVel1) + b3Dot3F4(a1, angVel1);
}


float calcJacCoeff(b3Float4ConstArg linear0, b3Float4ConstArg linear1, b3Float4ConstArg angular0, b3Float4ConstArg angular1,
					float invMass0, const b3Mat3x3* invInertia0, float invMass1, const b3Mat3x3* invInertia1)
{
	//	linear0,1 are normlized
	float jmj0 = invMass0;//b3Dot3F4(linear0, linear0)*invMass0;
	float jmj1 = b3Dot3F4(mtMul3(angular0,*invInertia0), angular0);
	float jmj2 = invMass1;//b3Dot3F4(linear1, linear1)*invMass1;
	float jmj3 = b3Dot3F4(mtMul3(angular1,*invInertia1), angular1);
	return -1.f/(jmj0+jmj1+jmj2+jmj3);
}


void setConstraint4( b3Float4ConstArg posA, b3Float4ConstArg linVelA, b3Float4ConstArg angVelA, float invMassA, b3Mat3x3ConstArg invInertiaA,
	b3Float4ConstArg posB, b3Float4ConstArg linVelB, b3Float4ConstArg angVelB, float invMassB, b3Mat3x3ConstArg invInertiaB, 
	__global struct b3Contact4Data* src, float dt, float positionDrift, float positionConstraintCoeff,
	b3ContactConstraint4_t* dstC )
{
	dstC->m_bodyA = abs(src->m_bodyAPtrAndSignBit);
	dstC->m_bodyB = abs(src->m_bodyBPtrAndSignBit);

	float dtInv = 1.f/dt;
	for(int ic=0; ic<4; ic++)
	{
		dstC->m_appliedRambdaDt[ic] = 0.f;
	}
	dstC->m_fJacCoeffInv[0] = dstC->m_fJacCoeffInv[1] = 0.f;


	dstC->m_linear = src->m_worldNormalOnB;
	dstC->m_linear.w = 0.7f ;//src->getFrictionCoeff() );
	for(int ic=0; ic<4; ic++)
	{
		b3Float4 r0 = src->m_worldPosB[ic] - posA;
		b3Float4 r1 = src->m_worldPosB[ic] - posB;

		if( ic >= src->m_worldNormalOnB.w )//npoints
		{
			dstC->m_jacCoeffInv[ic] = 0.f;
			continue;
		}

		float relVelN;
		{
			b3Float4 linear, angular0, angular1;
			setLinearAndAngular(src->m_worldNormalOnB, r0, r1, &linear, &angular0, &angular1);

			dstC->m_jacCoeffInv[ic] = calcJacCoeff(linear, -linear, angular0, angular1,
				invMassA, &invInertiaA, invMassB, &invInertiaB );

			relVelN = calcRelVel(linear, -linear, angular0, angular1,
				linVelA, angVelA, linVelB, angVelB);

			float e = 0.f;//src->getRestituitionCoeff();
			if( relVelN*relVelN < 0.004f ) e = 0.f;

			dstC->m_b[ic] = e*relVelN;
			//float penetration = src->m_worldPosB[ic].w;
			dstC->m_b[ic] += (src->m_worldPosB[ic].w + positionDrift)*positionConstraintCoeff*dtInv;
			dstC->m_appliedRambdaDt[ic] = 0.f;
		}
	}

	if( src->m_worldNormalOnB.w > 0 )//npoints
	{	//	prepare friction
		b3Float4 center = b3MakeFloat4(0.f,0.f,0.f,0.f);
		for(int i=0; i<src->m_worldNormalOnB.w; i++) 
			center += src->m_worldPosB[i];
		center /= (float)src->m_worldNormalOnB.w;

		b3Float4 tangent[2];
		b3PlaneSpace1(src->m_worldNormalOnB,&tangent[0],&tangent[1]);
		
		b3Float4 r[2];
		r[0] = center - posA;
		r[1] = center - posB;

		for(int i=0; i<2; i++)
		{
			b3Float4 linear, angular0, angular1;
			setLinearAndAngular(tangent[i], r[0], r[1], &linear, &angular0, &angular1);

			dstC->m_fJacCoeffInv[i] = calcJacCoeff(linear, -linear, angular0, angular1,
				invMassA, &invInertiaA, invMassB, &invInertiaB );
			dstC->m_fAppliedRambdaDt[i] = 0.f;
		}
		dstC->m_center = center;
	}

	for(int i=0; i<4; i++)
	{
		if( i<src->m_worldNormalOnB.w )
		{
			dstC->m_worldPos[i] = src->m_worldPosB[i];
		}
		else
		{
			dstC->m_worldPos[i] = b3MakeFloat4(0.f,0.f,0.f,0.f);
		}
	}
}