TriangleMesh.cpp

bool ActiveMesh::GetPointOnQuadricSurface(const float x,const float y,
                                          float &z1, float &z2,
                                          const float (&coeffs)[10])
{
	const float a=coeffs[9];
	const float b=coeffs[3] +coeffs[5]*x +coeffs[6]*y;
	const float c=coeffs[0] +coeffs[1]*x +coeffs[2]*y
	             +coeffs[4]*x*y +coeffs[7]*x*x +coeffs[8]*y*y;

	const float sqArg=b*b - 4*a*c;
	if (sqArg < 0.f) return false;
	if (a == 0.f) return false;

	z1=(-b + sqrtf(sqArg)) / (2.f*a);
	z2=(-b - sqrtf(sqArg)) / (2.f*a);

	return true;
}


float ActiveMesh::GetClosestPointOnQuadricSurface(Vector3F& point,
                                                  const float (&coeffs)[10])
{
	//backup original input coordinate
	const float x=point.x;
	const float y=point.y;
	const float z=point.z;
	float tmp1,tmp2;

	//list of possible coordinates
	std::vector<Vector3F> pointAdepts;

	//took a pair of coordinates, calculate the third one
	//and make it an adept...
	if (GetPointOnQuadricSurface(x,y,tmp1,tmp2,coeffs))
	{
		pointAdepts.push_back(Vector3F(x,y,tmp1));
		pointAdepts.push_back(Vector3F(x,y,tmp2));
	}
	if (GetPointOnQuadricSurface(x,z,tmp1,tmp2,coeffs))
	{
		pointAdepts.push_back(Vector3F(x,tmp1,z));
		pointAdepts.push_back(Vector3F(x,tmp2,z));
	}
	if (GetPointOnQuadricSurface(y,z,tmp1,tmp2,coeffs))
	{
		pointAdepts.push_back(Vector3F(tmp1,y,z));
		pointAdepts.push_back(Vector3F(tmp2,y,z));
	}

	//are we doomed?
	if (pointAdepts.size() == 0)
		return (-999999.f);

	//find the closest
	int closestIndex=ChooseClosestPoint(pointAdepts,point);
	
	//calc distance to it
	point-=pointAdepts[closestIndex];
	tmp1=point.Len();

	//adjust the input/output point
	point=pointAdepts[closestIndex];

	return (tmp1);
}


int ActiveMesh::ChooseClosestPoint(const std::vector<Vector3F>& points,
                                   const Vector3F& point)
{
	int minIndex=-1;
	float minSqDist=9999999999999.f;

	Vector3F p;
	for (unsigned int i=0; i < points.size(); ++i)
	{
		p=point;
		p-=points[i];
		if (p.LenQ() < minSqDist)
		{
			minIndex=i;
			minSqDist=p.LenQ();
		}
	}

	return minIndex;
}