/usr/include/libwildmagic/Wm5Ellipse2.h is in libwildmagic-dev 5.13-1ubuntu3.
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// Copyright (c) 1998-2014
// Distributed under the Boost Software License, Version 1.0.
// http://www.boost.org/LICENSE_1_0.txt
// http://www.geometrictools.com/License/Boost/LICENSE_1_0.txt
//
// File Version: 5.0.0 (2010/01/01)
#ifndef WM5ELLIPSE2_H
#define WM5ELLIPSE2_H
#include "Wm5MathematicsLIB.h"
#include "Wm5EigenDecomposition.h"
namespace Wm5
{
template <typename Real>
class Ellipse2
{
public:
// An ellipse has center K, axis directions U[0] and U[1] (both
// unit-length vectors), and extents e[0] and e[1] (both positive
// numbers). A point X = K+y[0]*U[0]+y[1]*U[1] is on the ellipse whenever
// (y[0]/e[0])^2+(y[1]/e[1])^2 = 1. The test for a point inside the
// ellipse uses "<=" instead of "=" in the previous expression. An
// algebraic representation for the ellipse is
// 1 = (X-K)^T * (U[0]*U[0]^T/e[0]^2 + U[1]*U[1]^T/e[1]^2) * (X-K)
// = (X-K)^T * M * (X-K)
// where the superscript T denotes transpose. Observe that U[i]*U[i]^T
// is a matrix, not a scalar dot product. The matrix M is symmetric.
// The ellipse is also represented by a quadratic equation
// 0 = a0 + a1*x[0] + a2*x[1] + a3*x[0]^2 + a4*x[0]*x[1] + a5*x[1]^2
// = a0 + [a1 a2]*X + X^T*[a3 a4/2]*X
// [a4/2 a5 ]
// = C + B^T*X + X^T*A*X
// where X = (x[0],x[1]). This equation can be factored to the form
// (X-K)^T*M*(X-K) = 1, where K = -A^{-1}*B/2, M = A/(B^T*A^{-1}*B/4-C).
// To be an ellipse, M must have all positive eigenvalues.
// Construction and destruction.
Ellipse2 (); // uninitialized
~Ellipse2 ();
Ellipse2 (const Vector2<Real>& center, const Vector2<Real> axis[2],
const Real extent[2]);
Ellipse2 (const Vector2<Real>& center, const Vector2<Real>& axis0,
const Vector2<Real>& axis1, const Real extent0, const Real extent1);
// Compute M = sum_{i=0}^1 U[i]*U[i]^T/e[i]^2.
void GetM (Matrix2<Real>& M) const;
// Compute M^{-1} = sum_{i=0}^1 U[i]*U[i]^T*e[i]^2.
void GetMInverse (Matrix2<Real>& MInverse) const;
// Construct the coefficients in the quadratic equation that represents
// the ellipse. 'coeff' stores a0 through a5. 'A', 'B', and 'C' are as
// described in the comments before the constructors.
void ToCoefficients (Real coeff[6]) const;
void ToCoefficients (Matrix2<Real>& A, Vector2<Real>& B,
Real& C) const;
// Construct C, U[i], and e[i] from the quadratic equation. The return
// value is 'true' if and only if the input coefficients represent an
// ellipse. If the function returns 'false', the ellipse data members
// are undefined. 'coeff' stores a0 through a5. 'A', 'B', and 'C' are as
// described in the comments before the constructors.
bool FromCoefficients (const Real coeff[6]);
bool FromCoefficients (const Matrix2<Real>& A,
const Vector2<Real>& B, Real C);
// Evaluate the quadratic function Q(X) = (X-K)^T * M * (X-K) - 1.
Real Evaluate (const Vector2<Real>& point) const;
// Test whether the input point is inside or on the ellipse. The point
// is contained when Q(X) <= 0, where Q(X) is the function in the comment
// before the function Evaluate().
bool Contains (const Vector2<Real>& point) const;
Vector2<Real> Center;
Vector2<Real> Axis[2];
Real Extent[2];
private:
static void Convert (const Real coeff[6], Matrix2<Real>& A,
Vector2<Real>& B, Real& C);
static void Convert (const Matrix2<Real>& A, const Vector2<Real>& B,
Real C, Real coeff[6]);
};
#include "Wm5Ellipse2.inl"
typedef Ellipse2<float> Ellipse2f;
typedef Ellipse2<double> Ellipse2d;
}
#endif
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