UT_Matrix2.h

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/*
 * PROPRIETARY INFORMATION.  This software is proprietary to
 * Side Effects Software Inc., and is not to be reproduced,
 * transmitted, or disclosed in any way without written permission.
 *
 */

#pragma once

#ifndef __UT_Matrix2_h__
#define __UT_Matrix2_h__

#include "UT_API.h"
#include "UT_Assert.h"
#include "UT_FixedVectorTraits.h"
#include "UT_VectorTypes.h"

#include <SYS/SYS_Types.h>
#include <SYS/SYS_Math.h>
#include <SYS/SYS_StaticAssert.h>
#include <iosfwd>

class UT_IStream;
class UT_JSONWriter;
class UT_JSONValue;
class UT_JSONParser;

// Free floating operators that return a UT_Matrix2T<T> object. 
template <typename T> UT_API
UT_Matrix2T<T>  operator+(const UT_Matrix2T<T> &m1, const UT_Matrix2T<T> &m2);
template <typename T, typename S> UT_API
UT_Matrix2T<T>  operator+(const UT_Matrix2T<T> &m, const UT_Vector2T<S> &v);
template <typename T, typename S> static inline
UT_Matrix2T<T>  operator+(const UT_Vector2T<S> &v, const UT_Matrix2T<T> &m);
template <typename T> UT_API
UT_Matrix2T<T>  operator+(const UT_Matrix2T<T> &mat, T sc);
template <typename T> static inline
UT_Matrix2T<T>  operator+(T sc, const UT_Matrix2T<T> &mat);

template <typename T> UT_API
UT_Matrix2T<T>  operator-(const UT_Matrix2T<T> &m1, const UT_Matrix2T<T> &m2);
template <typename T, typename S> UT_API
UT_Matrix2T<T>  operator-(const UT_Matrix2T<T> &m, const UT_Vector2T<S> &v);
template <typename T, typename S> UT_API
UT_Matrix2T<T>  operator-(const UT_Vector2T<S> &v, const UT_Matrix2T<T> &m);
template <typename T> static inline
UT_Matrix2T<T>  operator-(const UT_Matrix2T<T> &mat, T sc);
template <typename T> UT_API
UT_Matrix2T<T>  operator-(T sc, const UT_Matrix2T<T> &mat);

template <typename T> UT_API
UT_Matrix2T<T> operator*(const UT_Matrix2T<T> &m1, const UT_Matrix2T<T> &m2);
template <typename T,typename S> UT_API
UT_Matrix2T<T> operator*(const UT_Matrix2T<T> &mat, S sc);
template <typename T,typename S> static inline
UT_Matrix2T<T> operator*(S sc, const UT_Matrix2T<T> &mat);

template <typename T> static inline
UT_Matrix2T<T>  operator/(const UT_Matrix2T<T> &mat, T sc);
template <typename T> UT_API
UT_Matrix2T<T>  operator/(T sc, const UT_Matrix2T<T> &mat);

template <typename T>
inline UT_Matrix2T<T>   SYSmin  (const UT_Matrix2T<T> &v1, const UT_Matrix2T<T> &v2);
template <typename T>
inline UT_Matrix2T<T>   SYSmax  (const UT_Matrix2T<T> &v1, const UT_Matrix2T<T> &v2);
template <typename T,typename S>
inline UT_Matrix2T<T> SYSlerp(const UT_Matrix2T<T> &v1, const UT_Matrix2T<T> &v2, S t);

/// Bilinear interpolation
template <typename T,typename S>
inline UT_Matrix2T<T> SYSbilerp(const UT_Matrix2T<T> &u0v0, const UT_Matrix2T<T> &u1v0,
                                  const UT_Matrix2T<T> &u0v1, const UT_Matrix2T<T> &u1v1,
                                  S u, S v)
{ return SYSlerp(SYSlerp(u0v0, u0v1, v), SYSlerp(u1v0, u1v1, v), u); }

/// Barycentric interpolation
template <typename T, typename S>
inline UT_Matrix2T<T> SYSbarycentric(const UT_Matrix2T<T> &v0,
        const UT_Matrix2T<T> &v1, const UT_Matrix2T<T> &v2, S u, S v)
{ return v0 * (1 - u - v) + v1 * u + v2 *v; }


/// This class implements a 2x2 matrix in row-major order.
///
/// Most of Houdini operates with row vectors that are left-multiplied with
/// matrices. e.g.,   z = v * M
template <typename T>
class UT_API UT_Matrix2T
{
public:

    typedef T value_type;
    static constexpr int tuple_size = 4;

    /// Construct uninitialized matrix.
    SYS_FORCE_INLINE UT_Matrix2T() = default;

    /// Default copy constructor
    constexpr UT_Matrix2T(const UT_Matrix2T &) = default;

    /// Default move constructor
    constexpr UT_Matrix2T(UT_Matrix2T &&) = default;

    /// Construct identity matrix, multipled by scalar.
    explicit constexpr UT_Matrix2T(T val) noexcept
        : matx{{val,T(0)},{T(0),val}}
    {
        SYS_STATIC_ASSERT(sizeof(UT_Matrix2T<T>) == tuple_size * sizeof(T));
    }
    /// Construct a deep copy of the input row-major data.
    /// @{
    explicit constexpr UT_Matrix2T(const fpreal32 m[2][2]) noexcept
        : matx{{T(m[0][0]),T(m[0][1])},{T(m[1][0]),T(m[1][1])}}
    {}
    explicit constexpr UT_Matrix2T(const fpreal64 m[2][2]) noexcept
        : matx{{T(m[0][0]),T(m[0][1])},{T(m[1][0]),T(m[1][1])}}
    {}
    /// @}

    /// This constructor is for convenience.
    constexpr UT_Matrix2T(T val00, T val01, T val10, T val11) noexcept
        : matx{{val00,val01},{val10,val11}}
    {}

    /// Base type conversion constructor
    template <typename S>
    UT_Matrix2T(const UT_Matrix2T<S> &m) noexcept
        : matx{{T(m(0,0)),T(m(0,1))},{T(m(1,0)),T(m(1,1))}}
    {}

    /// Conversion to a 2x2 from a 3x3 matrix by ignoring the
    /// last row and last column.
    template <typename S>
    explicit UT_Matrix2T(const UT_Matrix3T<S> &m) noexcept
        : matx{{T(m(0,0)),T(m(0,1))},{T(m(1,0)),T(m(1,1))}}
    {}

    /// Default copy assignment operator
    UT_Matrix2T<T> &operator=(const UT_Matrix2T<T> &m) = default;

    /// Default move assignment operator
    UT_Matrix2T<T> &operator=(UT_Matrix2T<T> &&m) = default;

    /// Conversion operator that returns a 2x2 from a 3x3 matrix by ignoring the
    /// last row and last column.
    template <typename S>
    UT_Matrix2T<T>      &operator=(const UT_Matrix3T<S> &m);

    UT_Matrix2T<T> operator-() const
    {
        return UT_Matrix2T<T>(
            -matx[0][0], -matx[0][1],
            -matx[1][0], -matx[1][1]);
    }

    UT_Matrix2T<T>      &operator+=(const UT_Matrix2T<T> &m)
                        {
                            matx[0][0]+=m.matx[0][0]; matx[0][1]+=m.matx[0][1];
                            matx[1][0]+=m.matx[1][0]; matx[1][1]+=m.matx[1][1];
                            return *this;
                        }
    UT_Matrix2T<T>      &operator-=(const UT_Matrix2T<T> &m)
                        {
                            matx[0][0]-=m.matx[0][0]; matx[0][1]-=m.matx[0][1];
                            matx[1][0]-=m.matx[1][0]; matx[1][1]-=m.matx[1][1];
                            return *this;
                        }
    UT_Matrix2T<T>      &operator*=(const UT_Matrix2T<T> &m);

    constexpr bool operator==(const UT_Matrix2T<T> &m) const noexcept
    {
        return (&m == this) || (
            matx[0][0]==m(0,0) && matx[0][1]==m(0,1) &&
            matx[1][0]==m(1,0) && matx[1][1]==m(1,1) );
    }
    constexpr bool operator!=(const UT_Matrix2T<T> &m) const noexcept
                {
                    return !(*this == m);
                }

    UT_Matrix2T<T>  &operator=(T val)
                    {
                        matx[0][0] = val; matx[0][1] = 0;
                        matx[1][0] = 0;   matx[1][1] = val;
                        return *this;
                    }
    UT_Matrix2T<T>  &operator+=(T scalar)
                    {
                        matx[0][0]+=scalar; matx[0][1]+=scalar;
                        matx[1][0]+=scalar; matx[1][1]+=scalar;
                        return *this;
                    }
    UT_Matrix2T<T>  &operator-=(T scalar)
                    {
                        return operator+=(-scalar);
                    }
    UT_Matrix2T<T>  &operator*=(T scalar)
                    {
                        matx[0][0]*=scalar; matx[0][1]*=scalar;
                        matx[1][0]*=scalar; matx[1][1]*=scalar;
                        return *this;
                    }
    UT_Matrix2T<T>  &operator/=(T scalar)
                    {
                        return operator*=( T(1)/scalar );
                    }

    // Vector2 operators:
    template <typename S>
    inline
    UT_Matrix2T<T>  &operator=(const UT_Vector2T<S> &vec);
    template <typename S>
    inline
    UT_Matrix2T<T>  &operator+=(const UT_Vector2T<S> &vec);
    template <typename S>
    inline
    UT_Matrix2T<T>  &operator-=(const UT_Vector2T<S> &vec);

    constexpr T determinant() const noexcept
                {
                    return matx[0][0]*matx[1][1] - matx[0][1]*matx[1][0];
                }
    constexpr T trace() const noexcept
                { return matx[0][0] + matx[1][1]; }

    /// Returns eigenvalues of this matrix
    template <typename S>
    int         eigenvalues(UT_Vector2T<S> &r, UT_Vector2T<S> &i) const;

    /// Invert this matrix and return 0 if OK, 1 if singular.
    /// If singular, the matrix will be unchanged.
    int         invert()
    {
        // NOTE: The other invert function should work on *this,
        //       since it does all reading before all writing.
        return invert(*this);
    }

    /// Invert the matrix and return 0 if OK, 1 if singular.
    /// Puts the inverted matrix in m, and leaves this matrix unchanged.
    /// If singular, the matrix will be unchanged.
    int         invert(UT_Matrix2T<T> &m) const
    {
        // Effectively rescale the matrix for the determinant check,
        // because if the whole matrix is close to zero, having a
        // small determinant may be fine.
        T scale2 = SYSmax(matx[0][0]*matx[0][0],
                          matx[0][1]*matx[0][1],
                          matx[1][0]*matx[1][0],
                          matx[1][1]*matx[1][1]);
        T det = determinant();
        if (!SYSequalZero(det, tolerance()*scale2))
        {
            // Finish all reading before writing to m,
            // so that invert() can call invert(*this)
            m = UT_Matrix2T<T>( matx[1][1],-matx[0][1],
                               -matx[1][0], matx[0][0]);
            m *= (T(1)/det);

            return 0;
        }
        return 1;
    }

    /// Returns the tolerance of our class.
    T           tolerance() const;

    // Solve a 2x2 system of equations Ax=b, where A is this matrix, b is
    // given and x is unknown. The method returns 0 if the determinant is not
    // 0, and 1 otherwise.
    template <typename S>
    int         solve(const UT_Vector2T<S> &b, UT_Vector2T<S> &x) const
    {
        // Effectively rescale the matrix for the determinant check,
        // because if the whole matrix is close to zero, having a
        // small determinant may be fine.
        T scale2 = SYSmax(matx[0][0]*matx[0][0],
                          matx[0][1]*matx[0][1],
                          matx[1][0]*matx[1][0],
                          matx[1][1]*matx[1][1]);
        T det = determinant();
        if (!SYSequalZero(det, tolerance()*scale2))
        {
            T recipdet = T(1)/det;
            x = UT_Vector2T<S>(
                    recipdet * (matx[1][1]*b.x() - matx[0][1]*b.y()),
                    recipdet * (matx[0][0]*b.y() - matx[1][0]*b.x()));
            return 0;
        }
        return 1;
    }

    // Solve a 2x2 system of equations xA=b, where A is this matrix, b is
    // given and x is unknown. The method returns 0 if the determinant is not
    // 0, and 1 otherwise.
    template <typename S>
    int         solveTranspose(const UT_Vector2T<S> &b, UT_Vector2T<S> &x) const
    {
        // Effectively rescale the matrix for the determinant check,
        // because if the whole matrix is close to zero, having a
        // small determinant may be fine.
        T scale2 = SYSmax(matx[0][0]*matx[0][0],
                          matx[0][1]*matx[0][1],
                          matx[1][0]*matx[1][0],
                          matx[1][1]*matx[1][1]);
        T det = determinant();
        if (!SYSequalZero(det, tolerance()*scale2))
        {
            T recipdet = T(1)/det;
            x = UT_Vector2T<S>(
                    recipdet * (matx[1][1]*b.x() - matx[1][0]*b.y()),
                    recipdet * (matx[0][0]*b.y() - matx[0][1]*b.x()));
            return 0;
        }
        return 1;
    }

    // Transpose this matrix or return its transpose.
    void        transpose()
                {
                    T tmp;
                    tmp=matx[0][1];  matx[0][1]=matx[1][0];  matx[1][0]=tmp;
                }
    UT_Matrix2T<T>      transpose() const;

    // check for equality within a tolerance level
    bool        isEqual( const UT_Matrix2T<T> &m,
                         T tolerance=T(SYS_FTOLERANCE) ) const
                {
                    return (&m == this) || (
                    SYSisEqual( matx[0][0], m.matx[0][0], tolerance ) &&
                    SYSisEqual( matx[0][1], m.matx[0][1], tolerance ) &&

                    SYSisEqual( matx[1][0], m.matx[1][0], tolerance ) &&
                    SYSisEqual( matx[1][1], m.matx[1][1], tolerance ) );
                }

    // Matrix += b * v1 * v2T
    template <typename S>
    void        outerproductUpdate(T b, 
                             const UT_Vector2T<S> &v1, const UT_Vector2T<S> &v2)
    {
        T bv1;
        bv1 = b * v1.x();
        matx[0][0]+=bv1*v2.x();
        matx[0][1]+=bv1*v2.y();
        bv1 = b * v1.y();
        matx[1][0]+=bv1*v2.x();
        matx[1][1]+=bv1*v2.y();
    }

    /// Set the matrix to identity
    void        identity()
                {
                    matx[0][0]=(T)1;matx[0][1]=(T)0;
                    matx[1][0]=(T)0;matx[1][1]=(T)1;
                }
    /// Set the matrix to zero
    void        zero()          { *this = 0; }

    bool isIdentity() const
    {
        // NB: DO NOT USE TOLERANCES
        return(
            matx[0][0]==1 && matx[0][1]==0 &&
            matx[1][0]==0 && matx[1][1]==1);
    }
    bool isZero() const
    {
        // NB: DO NOT USE TOLERANCES
        return (
            matx[0][0]==0 && matx[0][1]==0 &&
            matx[1][0]==0 && matx[1][1]==0);
    }

    /// Create a rotation matrix for the given angle in radians
    static UT_Matrix2T<T>       rotationMat(T theta);

    /// Rotate by theta radians
    void        rotate(T theta)
                    { (*this) *= rotationMat(theta); }

    /// Multiply this matrix by a scale matrix with diagonal (sx, sy):
    /// @{
    void        scale(T sx, T sy)
                {
                    matx[0][0] *= sx; matx[0][1] *= sy; 
                    matx[1][0] *= sx; matx[1][1] *= sy;
                }
    inline void scale(const UT_Vector2T<T> &s)
                { scale(s(0), s(1)); }
    /// @}

    /// Initialize this matrix to zero.
    void        initialize()
                {
                    matx[0][0]=matx[0][1]= (T)0;
                    matx[1][0]=matx[1][1]= (T)0;
                }

    /// Return a matrix entry. No bounds checking on subscripts.
    // @{
    SYS_FORCE_INLINE T &operator()(unsigned row, unsigned col) noexcept
                 {
                     UT_ASSERT_P(row < 2 && col < 2);
                     return matx[row][col];
                 }
    SYS_FORCE_INLINE T operator()(unsigned row, unsigned col) const noexcept
                 {
                     UT_ASSERT_P(row < 2 && col < 2);
                     return matx[row][col];
                 }
    // @}

    /// Return the raw matrix data.
    // @{
    const T     *data() const   { return myFloats; }
    T           *data()         { return myFloats; }
    // @}

    /// Compute a hash
    unsigned    hash() const    { return SYSvector_hash(data(), tuple_size); }

    /// Return a matrix row. No bounds checking on subscript.
    // @{
    T           *operator()(unsigned row)
                 {
                     UT_ASSERT_P(row < 2);
                     return matx[row];
                 }
    const T     *operator()(unsigned row) const
                 {
                     UT_ASSERT_P(row < 2);
                     return matx[row];
                 }
    inline
    const UT_Vector2T<T> &operator[](unsigned row) const;
    inline
    UT_Vector2T<T> &operator[](unsigned row);
    // @}

    /// Dot product with another matrix
    /// Does dot(a,b) = sum_ij a_ij * b_ij
    T dot(const UT_Matrix2T<T> &m) const;
        
    /// Euclidean or Frobenius norm of a matrix.
    /// Does sqrt(sum(a_ij ^2))
    T            getEuclideanNorm() const
                 { return SYSsqrt(getEuclideanNorm2()); }
    /// Euclidean norm squared.
    T            getEuclideanNorm2() const;

    /// Get the 1-norm of this matrix, assuming a row vector convention.
    /// Returns the maximum absolute row sum. ie. max_i(sum_j(abs(a_ij)))
    T            getNorm1() const;

    /// Get the inf-norm of this matrix, assuming a row vector convention.
    /// Returns the maximum absolute column sum. ie. max_j(sum_i(abs(a_ij)))
    T            getNormInf() const;

    /// Get the max-norm of this matrix
    /// Returns the maximum absolute entry. ie. max_j(max_i(abs(a_ij)))
    T            getNormMax() const;

    // I/O methods.  Return 0 if read/write successful, -1 if unsuccessful.
    int                  save(std::ostream &os, int binary) const;
    bool                 load(UT_IStream &is);

    void                 outAsciiNoName(std::ostream &os) const;

    /// @{
    /// Methods to serialize to a JSON stream.  The matrix is stored as an
    /// array of 4 reals.
    bool                save(UT_JSONWriter &w) const;
    bool                save(UT_JSONValue &v) const;
    bool                load(UT_JSONParser &p);
    /// @}

    // I/O friends:
    friend std::ostream &operator<<(std::ostream &os, const UT_Matrix2T<T> &v)
                        {
                            // v.className(os);
                            v.outAsciiNoName(os);
                            return os;
                        }

    /// Returns the vector size
    static int          entries()       { return tuple_size; }

private:
    void                 writeClassName(std::ostream &os) const;
    static const char   *className();
    
    union {
        T       matx[2][2];
        T       myFloats[tuple_size];
    };
};

#include "UT_Vector2.h"

template <>
inline
float UT_Matrix2T<float>::tolerance() const
{
    return 1e-5f;
}

template <>
inline
double UT_Matrix2T<double>::tolerance() const
{
    return 1e-11;
}

// Special instantiations to handle the fact that we have UT_Vector2T<int64>::getBary()
template <>
inline
int32 UT_Matrix2T<int32>::tolerance() const
{
    return 0;
}

template <>
inline
int64 UT_Matrix2T<int64>::tolerance() const
{
    return 0;
}

template <typename T>
template <typename S>
inline 
UT_Matrix2T<T>  &UT_Matrix2T<T>::operator=(const UT_Vector2T<S> &vec)
{
    matx[0][0] = matx[0][1] = vec.x();
    matx[1][0] = matx[1][1] = vec.y();
    return *this;
}

template <typename T>
template <typename S>
inline
UT_Matrix2T<T>  &UT_Matrix2T<T>::operator+=(const UT_Vector2T<S> &vec)
{
    matx[0][0]+=vec.x(); matx[0][1]+=vec.x();
    matx[1][0]+=vec.y(); matx[1][1]+=vec.y();
    return *this;
}

template <typename T>
template <typename S>
inline
UT_Matrix2T<T>  &UT_Matrix2T<T>::operator-=(const UT_Vector2T<S> &vec)
{
    matx[0][0]-=vec.x(); matx[0][1]-=vec.x();
    matx[1][0]-=vec.y(); matx[1][1]-=vec.y();
    return *this;
}

template <typename T>
inline
const UT_Vector2T<T> &UT_Matrix2T<T>::operator[](unsigned row) const
{
    UT_ASSERT_P(row < 2);
    return *(const UT_Vector2T<T>*)(matx[row]);
}

template <typename T>
inline
UT_Vector2T<T> &UT_Matrix2T<T>::operator[](unsigned row)
{
    UT_ASSERT_P(row < 2);
    return *(UT_Vector2T<T>*)(matx[row]);
}


// Free floating functions:
template <typename T, typename S>
static inline
UT_Matrix2T<T>      operator+(const UT_Vector2T<S> &vec, const UT_Matrix2T<T> &mat)
{
    return mat+vec;
}

template <typename T>
static inline
UT_Matrix2T<T>      operator+(T sc, const UT_Matrix2T<T> &m1)
{
    return m1+sc;
}

template <typename T>
static inline
UT_Matrix2T<T>      operator-(const UT_Matrix2T<T> &m1, T sc)
{
    return m1+(-sc);
}

template <typename T,typename S>
static inline
UT_Matrix2T<T>      operator*(S sc, const UT_Matrix2T<T> &m1)
{
    return m1*sc;
}

template <typename T>
static inline
UT_Matrix2T<T>      operator/(const UT_Matrix2T<T> &m1, T scalar)
{
    return m1 * (T(1)/scalar);
}

template <typename T>
static inline
T dot(const UT_Matrix2T<T> &m1, const UT_Matrix2T<T> &m2){
  return m1.dot(m2);
}

template <typename T>
inline
UT_Matrix2T<T>  SYSmin(const UT_Matrix2T<T> &v1, const UT_Matrix2T<T> &v2)
{
    return UT_Matrix2T<T>(
            SYSmin(v1(0,0), v2(0,0)),
            SYSmin(v1(0,1), v2(0,1)),
            SYSmin(v1(1,0), v2(1,0)),
            SYSmin(v1(1,1), v2(1,1))
    );
}

template <typename T>
inline
UT_Matrix2T<T>  SYSmax(const UT_Matrix2T<T> &v1, const UT_Matrix2T<T> &v2)
{
    return UT_Matrix2T<T>(
            SYSmax(v1(0,0), v2(0,0)),
            SYSmax(v1(0,1), v2(0,1)),
            SYSmax(v1(1,0), v2(1,0)),
            SYSmax(v1(1,1), v2(1,1))
    );
}

template <typename T,typename S>
inline
UT_Matrix2T<T> SYSlerp(const UT_Matrix2T<T> &v1, const UT_Matrix2T<T> &v2, S t)
{
    return UT_Matrix2T<T>(
            SYSlerp(v1(0,0), v2(0,0), t),
            SYSlerp(v1(0,1), v2(0,1), t),
            SYSlerp(v1(1,0), v2(1,0), t),
            SYSlerp(v1(1,1), v2(1,1), t)
    );
}

#ifndef UT_DISABLE_VECTORIZE_MATRIX
template <>
inline
UT_Matrix2T<float> SYSlerp(const UT_Matrix2T<float> &v1, const UT_Matrix2T<float> &v2, float t)
{
    const v4uf l(v1.data());
    const v4uf r(v2.data());

    UT_Matrix2T<float> result_mat;
    vm_store(result_mat.data(), SYSlerp(l, r, t).vector);
    return result_mat;
}
#endif

template< typename T, exint D >
class UT_FixedVector;

template<typename T>
struct UT_FixedVectorTraits<UT_Matrix2T<T> >
{
    typedef UT_FixedVector<T,4> FixedVectorType;
    typedef T DataType;
    static const exint TupleSize = 4;
    static const bool isVectorType = true;
};

// Overload for custom formatting of UT_Matrix2T<T> with UTformat.
template<typename T>
UT_API size_t format(char *buffer, size_t buffer_size, const UT_Matrix2T<T> &v);

// UT_Matrix2TFromFixed<T> is a function object that
// creates a UT_Matrix2T<T> from a fixed array-like type TS,
// examples of which include T[4], UT_FixedVector<T,4> and UT_FixedArray<T,4> (AKA std::array<T,4>)
template <typename T>
struct UT_Matrix2TFromFixed
{    
    template< typename TS >
    constexpr SYS_FORCE_INLINE UT_Matrix2T<T> operator()(const TS& as) const noexcept
    {                
        SYS_STATIC_ASSERT( SYS_IsFixedArrayOf_v< TS, T, 2 * 2 > );

        return UT_Matrix2T<T>{as[0], as[1], as[2], as[3]};
    }
};

// Convert a fixed array-like type TS into a UT_Matrix2T< T >.
// This allows conversion to UT_Matrix2T without fixing T.
// Instead, the element type of TS determines the type T.
template< typename TS >
constexpr UT_Matrix2T< SYS_FixedArrayElement_t< TS > >
UTmakeMatrix2T( const TS& as ) noexcept
{
    using T = SYS_FixedArrayElement_t< TS >;

    return UT_Matrix2TFromFixed< T >{}( as );
} 

// UT_FromFixed<V> creates a V from a flat, fixed array-like representation

// Primary
template <typename V >
struct UT_FromFixed;

// Partial specialization for UT_Matrix2T
template <typename T>
struct UT_FromFixed< UT_Matrix2T<T> > : UT_Matrix2TFromFixed<T> {};

#endif