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✏️ Editing: ImathFrustum.h

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#ifndef INCLUDED_IMATHFRUSTUM_H
#define INCLUDED_IMATHFRUSTUM_H

#include "ImathVec.h"
#include "ImathPlane.h"
#include "ImathLine.h"
#include "ImathMatrix.h"
#include "ImathLimits.h"
#include "ImathFun.h"
#include "ImathNamespace.h"

#include "IexMathExc.h"

IMATH_INTERNAL_NAMESPACE_HEADER_ENTER

//
//  template class Frustum<T>
//
//  The frustum is always located with the eye point at the
//  origin facing down -Z. This makes the Frustum class
//  compatable with OpenGL (or anything that assumes a camera
//  looks down -Z, hence with a right-handed coordinate system)
//  but not with RenderMan which assumes the camera looks down
//  +Z. Additional functions are provided for conversion from
//  and from various camera coordinate spaces.
//
//  nearPlane/farPlane: near/far are keywords used by Microsoft's
//  compiler, so we use nearPlane/farPlane instead to avoid
//  issues.

template<class T>
class Frustum
{
  public:
    Frustum();
    Frustum(const Frustum &);
    Frustum(T nearPlane, T farPlane, T left, T right, T top, T bottom, bool ortho=false);
    Frustum(T nearPlane, T farPlane, T fovx, T fovy, T aspect);
    virtual ~Frustum();

//--------------------
    // Assignment operator
    //--------------------

const Frustum &     operator = (const Frustum &);

//--------------------
    //  Operators:  ==, !=
    //--------------------
    
    bool                operator == (const Frustum<T> &src) const;
    bool                operator != (const Frustum<T> &src) const;

//--------------------------------------------------------
    //  Set functions change the entire state of the Frustum
    //--------------------------------------------------------

void                set(T nearPlane, T farPlane,
                            T left, T right,
                            T top, T bottom,
                            bool ortho=false);

void                set(T nearPlane, T farPlane, T fovx, T fovy, T aspect);

//------------------------------------------------------
    //	These functions modify an already valid frustum state
    //------------------------------------------------------

void                modifyNearAndFar(T nearPlane, T farPlane);
    void                setOrthographic(bool);

//--------------
    //  Access
    //--------------
    
    bool                orthographic() const  { return _orthographic; }
    T                   nearPlane() const     { return _nearPlane;    }
    T                   hither() const        { return _nearPlane;    }
    T                   farPlane() const      { return _farPlane;     }
    T                   yon() const           { return _farPlane;     }
    T                   left() const          { return _left;         }
    T                   right() const         { return _right;        }
    T                   bottom() const        { return _bottom;       }
    T                   top() const           { return _top;          }

//-----------------------------------------------------------------------
    //  Sets the planes in p to be the six bounding planes of the frustum, in
    //  the following order: top, right, bottom, left, near, far.
    //  Note that the planes have normals that point out of the frustum.
    //  The version of this routine that takes a matrix applies that matrix
    //  to transform the frustum before setting the planes.
    //-----------------------------------------------------------------------

void                planes(Plane3<T> p[6]) const;
    void                planes(Plane3<T> p[6], const Matrix44<T> &M) const;

//----------------------
    //  Derived Quantities
    //----------------------

T                   fovx() const;
    T                   fovy() const;
    T                   aspect() const;
    Matrix44<T>         projectionMatrix() const;
    bool                degenerate() const;

//-----------------------------------------------------------------------
    //  Takes a rectangle in the screen space (i.e., -1 <= left <= right <= 1 
    //  and -1 <= bottom <= top <= 1) of this Frustum, and returns a new
    //  Frustum whose near clipping-plane window is that rectangle in local
    //  space.  
    //-----------------------------------------------------------------------

Frustum<T>          window(T left, T right, T top, T bottom) const;

//----------------------------------------------------------
    // Projection is in screen space / Conversion from Z-Buffer
    //----------------------------------------------------------

Line3<T>            projectScreenToRay( const Vec2<T> & ) const;
    Vec2<T>             projectPointToScreen( const Vec3<T> & ) const;

T                   ZToDepth(long zval, long min, long max) const;
    T                   normalizedZToDepth(T zval) const;
    long                DepthToZ(T depth, long zmin, long zmax) const;

T                   worldRadius(const Vec3<T> &p, T radius) const;
    T                   screenRadius(const Vec3<T> &p, T radius) const;

protected:

Vec2<T>             screenToLocal( const Vec2<T> & ) const;
    Vec2<T>             localToScreen( const Vec2<T> & ) const;

protected:
    T                   _nearPlane;
    T                   _farPlane;
    T                   _left;
    T                   _right;
    T                   _top;
    T                   _bottom;
    bool                _orthographic;
};

template<class T>
inline Frustum<T>::Frustum()
{
    set(T (0.1),
        T (1000.0),
        T (-1.0),
        T (1.0),
        T (1.0),
        T (-1.0),
        false);
}

template<class T>
inline Frustum<T>::Frustum(const Frustum &f)
{
    *this = f;
}

template<class T>
inline Frustum<T>::Frustum(T n, T f, T l, T r, T t, T b, bool o)
{
    set(n,f,l,r,t,b,o);
}

template<class T>
inline Frustum<T>::Frustum(T nearPlane, T farPlane, T fovx, T fovy, T aspect)
{
    set(nearPlane,farPlane,fovx,fovy,aspect);
}

template<class T>
Frustum<T>::~Frustum()
{
}

template<class T>
const Frustum<T> &
Frustum<T>::operator = (const Frustum &f)
{
    _nearPlane    = f._nearPlane;
    _farPlane     = f._farPlane;
    _left         = f._left;
    _right        = f._right;
    _top          = f._top;
    _bottom       = f._bottom;
    _orthographic = f._orthographic;

return *this;
}

template <class T>
bool
Frustum<T>::operator == (const Frustum<T> &src) const
{
    return
        _nearPlane    == src._nearPlane   &&
        _farPlane     == src._farPlane    &&
        _left         == src._left   &&
        _right        == src._right  &&
        _top          == src._top    &&
        _bottom       == src._bottom &&
        _orthographic == src._orthographic;
}

template <class T>
inline bool
Frustum<T>::operator != (const Frustum<T> &src) const
{
    return !operator== (src);
}

template<class T>
void Frustum<T>::set(T n, T f, T l, T r, T t, T b, bool o)
{
    _nearPlane      = n;
    _farPlane       = f;
    _left           = l;
    _right          = r;
    _bottom         = b;
    _top            = t;
    _orthographic   = o;
}

template<class T>
void Frustum<T>::modifyNearAndFar(T n, T f)
{
    if ( _orthographic )
    {
        _nearPlane = n;
    }
    else
    {
        Line3<T>  lowerLeft( Vec3<T>(0,0,0), Vec3<T>(_left,_bottom,-_nearPlane) );
        Line3<T> upperRight( Vec3<T>(0,0,0), Vec3<T>(_right,_top,-_nearPlane) );
        Plane3<T> nearPlane( Vec3<T>(0,0,-1), n );

Vec3<T> ll,ur;
        nearPlane.intersect(lowerLeft,ll);
        nearPlane.intersect(upperRight,ur);

_left      = ll.x;
        _right     = ur.x;
        _top       = ur.y;
        _bottom    = ll.y;
        _nearPlane = n;
        _farPlane  = f;
    }

_farPlane = f;
}

template<class T>
void Frustum<T>::setOrthographic(bool ortho)
{
    _orthographic   = ortho;
}

template<class T>
void Frustum<T>::set(T nearPlane, T farPlane, T fovx, T fovy, T aspect)
{
    if (fovx != 0 && fovy != 0)
        throw IEX_NAMESPACE::ArgExc ("fovx and fovy cannot both be non-zero.");

const T two = static_cast<T>(2);

if (fovx != 0)
    {
        _right    = nearPlane * Math<T>::tan(fovx / two);
        _left     = -_right;
        _top      = ((_right - _left) / aspect) / two;
        _bottom   = -_top;
    }
    else
    {
        _top      = nearPlane * Math<T>::tan(fovy / two);
        _bottom   = -_top;
        _right    = (_top - _bottom) * aspect / two;
        _left     = -_right;
    }
    _nearPlane    = nearPlane;
    _farPlane     = farPlane;
    _orthographic = false;
}

template<class T>
T Frustum<T>::fovx() const
{
    return Math<T>::atan2(_right,_nearPlane) - Math<T>::atan2(_left,_nearPlane);
}

template<class T>
T Frustum<T>::fovy() const
{
    return Math<T>::atan2(_top,_nearPlane) - Math<T>::atan2(_bottom,_nearPlane);
}

template<class T>
T Frustum<T>::aspect() const
{
    T rightMinusLeft = _right-_left;
    T topMinusBottom = _top-_bottom;

if (abs(topMinusBottom) < 1 &&
        abs(rightMinusLeft) > limits<T>::max() * abs(topMinusBottom))
    {
        throw IEX_NAMESPACE::DivzeroExc ("Bad viewing frustum: "
                               "aspect ratio cannot be computed.");
    }

return rightMinusLeft / topMinusBottom;
}

template<class T>
Matrix44<T> Frustum<T>::projectionMatrix() const
{
    T rightPlusLeft  = _right+_left;
    T rightMinusLeft = _right-_left;

T topPlusBottom  = _top+_bottom;
    T topMinusBottom = _top-_bottom;

T farPlusNear    = _farPlane+_nearPlane;
    T farMinusNear   = _farPlane-_nearPlane;

if ((abs(rightMinusLeft) < 1 &&
         abs(rightPlusLeft) > limits<T>::max() * abs(rightMinusLeft)) ||
        (abs(topMinusBottom) < 1 &&
         abs(topPlusBottom) > limits<T>::max() * abs(topMinusBottom)) ||
        (abs(farMinusNear) < 1 &&
         abs(farPlusNear) > limits<T>::max() * abs(farMinusNear)))
    {
        throw IEX_NAMESPACE::DivzeroExc ("Bad viewing frustum: "
                                                 "projection matrix cannot be computed.");
    }

if ( _orthographic )
    {
        T tx = -rightPlusLeft / rightMinusLeft;
        T ty = -topPlusBottom / topMinusBottom;
        T tz = -farPlusNear   / farMinusNear;

if ((abs(rightMinusLeft) < 1 &&
             2 > limits<T>::max() * abs(rightMinusLeft)) ||
            (abs(topMinusBottom) < 1 &&
             2 > limits<T>::max() * abs(topMinusBottom)) ||
            (abs(farMinusNear) < 1 &&
             2 > limits<T>::max() * abs(farMinusNear)))
        {
            throw IEX_NAMESPACE::DivzeroExc ("Bad viewing frustum: "
                                                         "projection matrix cannot be computed.");
        }

T A  =  2 / rightMinusLeft;
        T B  =  2 / topMinusBottom;
        T C  = -2 / farMinusNear;

return Matrix44<T>( A,  0,  0,  0,
                            0,  B,  0,  0,
                            0,  0,  C,  0,
                            tx, ty, tz, 1.f );
    }
    else
    {
        T A =  rightPlusLeft / rightMinusLeft;
        T B =  topPlusBottom / topMinusBottom;
        T C = -farPlusNear   / farMinusNear;

T farTimesNear = -2 * _farPlane * _nearPlane;
        if (abs(farMinusNear) < 1 &&
            abs(farTimesNear) > limits<T>::max() * abs(farMinusNear))
        {
            throw IEX_NAMESPACE::DivzeroExc ("Bad viewing frustum: "
                                                         "projection matrix cannot be computed.");
        }

T D = farTimesNear / farMinusNear;

T twoTimesNear = 2 * _nearPlane;

if ((abs(rightMinusLeft) < 1 &&
             abs(twoTimesNear) > limits<T>::max() * abs(rightMinusLeft)) ||
            (abs(topMinusBottom) < 1 &&
             abs(twoTimesNear) > limits<T>::max() * abs(topMinusBottom)))
        {
            throw IEX_NAMESPACE::DivzeroExc ("Bad viewing frustum: "
                                                         "projection matrix cannot be computed.");
        }

T E = twoTimesNear / rightMinusLeft;
        T F = twoTimesNear / topMinusBottom;

return Matrix44<T>( E,  0,  0,  0,
                            0,  F,  0,  0,
                            A,  B,  C, -1,
                            0,  0,  D,  0 );
    }
}

template<class T>
bool Frustum<T>::degenerate() const
{
    return (_nearPlane == _farPlane) ||
           (_left == _right) ||
           (_top == _bottom);
}

template<class T>
Frustum<T> Frustum<T>::window(T l, T r, T t, T b) const
{
    // move it to 0->1 space

Vec2<T> bl = screenToLocal( Vec2<T>(l,b) );
    Vec2<T> tr = screenToLocal( Vec2<T>(r,t) );

return Frustum<T>(_nearPlane, _farPlane, bl.x, tr.x, tr.y, bl.y, _orthographic);
}

template<class T>
Vec2<T> Frustum<T>::screenToLocal(const Vec2<T> &s) const
{
    return Vec2<T>( _left + (_right-_left) * (1.f+s.x) / 2.f,
                    _bottom + (_top-_bottom) * (1.f+s.y) / 2.f );
}

template<class T>
Vec2<T> Frustum<T>::localToScreen(const Vec2<T> &p) const
{
    T leftPlusRight  = _left - T (2) * p.x + _right;
    T leftMinusRight = _left-_right;
    T bottomPlusTop  = _bottom - T (2) * p.y + _top;
    T bottomMinusTop = _bottom-_top;

if ((abs(leftMinusRight) < T (1) &&
         abs(leftPlusRight) > limits<T>::max() * abs(leftMinusRight)) ||
        (abs(bottomMinusTop) < T (1) &&
         abs(bottomPlusTop) > limits<T>::max() * abs(bottomMinusTop)))
    {
        throw IEX_NAMESPACE::DivzeroExc
            ("Bad viewing frustum: "
             "local-to-screen transformation cannot be computed");
    }

return Vec2<T>( leftPlusRight / leftMinusRight,
                    bottomPlusTop / bottomMinusTop );
}

template<class T>
Line3<T> Frustum<T>::projectScreenToRay(const Vec2<T> &p) const
{
    Vec2<T> point = screenToLocal(p);
    if (orthographic())
        return Line3<T>( Vec3<T>(point.x,point.y, 0.0),
                         Vec3<T>(point.x,point.y,-1.0));
    else
        return Line3<T>( Vec3<T>(0, 0, 0), Vec3<T>(point.x,point.y,-_nearPlane));
}

template<class T>
Vec2<T> Frustum<T>::projectPointToScreen(const Vec3<T> &point) const
{
    if (orthographic() || point.z == T (0))
        return localToScreen( Vec2<T>( point.x, point.y ) );
    else
        return localToScreen( Vec2<T>( point.x * _nearPlane / -point.z,
                                       point.y * _nearPlane / -point.z ) );
}

template<class T>
T Frustum<T>::ZToDepth(long zval,long zmin,long zmax) const
{
    int zdiff = zmax - zmin;

if (zdiff == 0)
    {
        throw IEX_NAMESPACE::DivzeroExc
            ("Bad call to Frustum::ZToDepth: zmax == zmin");
    }

if ( zval > zmax+1 ) zval -= zdiff;

T fzval = (T(zval) - T(zmin)) / T(zdiff);
    return normalizedZToDepth(fzval);
}

template<class T>
T Frustum<T>::normalizedZToDepth(T zval) const
{
    T Zp = zval * 2.0 - 1;

if ( _orthographic )
    {
        return   -(Zp*(_farPlane-_nearPlane) + (_farPlane+_nearPlane))/2;
    }
    else 
    {
        T farTimesNear = 2 * _farPlane * _nearPlane;
        T farMinusNear = Zp * (_farPlane - _nearPlane) - _farPlane - _nearPlane;

if (abs(farMinusNear) < 1 &&
            abs(farTimesNear) > limits<T>::max() * abs(farMinusNear))
        {
            throw IEX_NAMESPACE::DivzeroExc
                ("Frustum::normalizedZToDepth cannot be computed.  The "
                 "near and far clipping planes of the viewing frustum "
                 "may be too close to each other");
        }

return farTimesNear / farMinusNear;
    }
}

template<class T>
long Frustum<T>::DepthToZ(T depth,long zmin,long zmax) const
{
    long zdiff     = zmax - zmin;
    T farMinusNear = _farPlane-_nearPlane;

if ( _orthographic )
    {
        T farPlusNear = 2*depth + _farPlane + _nearPlane;

if (abs(farMinusNear) < 1 &&
            abs(farPlusNear) > limits<T>::max() * abs(farMinusNear))
        {
            throw IEX_NAMESPACE::DivzeroExc
                ("Bad viewing frustum: near and far clipping planes "
                 "are too close to each other");
        }

T Zp = -farPlusNear/farMinusNear;
        return long(0.5*(Zp+1)*zdiff) + zmin;
    }
    else 
    { 
        // Perspective

T farTimesNear = 2*_farPlane*_nearPlane;
        if (abs(depth) < 1 &&
            abs(farTimesNear) > limits<T>::max() * abs(depth))
        {
            throw IEX_NAMESPACE::DivzeroExc
                ("Bad call to DepthToZ function: value of `depth' "
                 "is too small");
        }

T farPlusNear = farTimesNear/depth + _farPlane + _nearPlane;
        if (abs(farMinusNear) < 1 &&
            abs(farPlusNear) > limits<T>::max() * abs(farMinusNear))
        {
            throw IEX_NAMESPACE::DivzeroExc
                ("Bad viewing frustum: near and far clipping planes "
                 "are too close to each other");
        }

T Zp = farPlusNear/farMinusNear;
        return long(0.5*(Zp+1)*zdiff) + zmin;
    }
}

template<class T>
T Frustum<T>::screenRadius(const Vec3<T> &p, T radius) const
{
    // Derivation:
    // Consider X-Z plane.
    // X coord of projection of p = xp = p.x * (-_nearPlane / p.z)
    // Let q be p + (radius, 0, 0).
    // X coord of projection of q = xq = (p.x - radius)  * (-_nearPlane / p.z)
    // X coord of projection of segment from p to q = r = xp - xq
    //         = radius * (-_nearPlane / p.z)
    // A similar analysis holds in the Y-Z plane.
    // So r is the quantity we want to return.

if (abs(p.z) > 1 || abs(-_nearPlane) < limits<T>::max() * abs(p.z))
    {
        return radius * (-_nearPlane / p.z);
    }
    else
    {
        throw IEX_NAMESPACE::DivzeroExc
            ("Bad call to Frustum::screenRadius: the magnitude of `p' "
             "is too small");
    }

return radius * (-_nearPlane / p.z);
}

template<class T>
T Frustum<T>::worldRadius(const Vec3<T> &p, T radius) const
{
    if (abs(-_nearPlane) > 1 || abs(p.z) < limits<T>::max() * abs(-_nearPlane))
    {
        return radius * (p.z / -_nearPlane);
    }
    else
    {
        throw IEX_NAMESPACE::DivzeroExc
            ("Bad viewing frustum: the near clipping plane is too "
             "close to zero");
    }
}

template<class T>
void Frustum<T>::planes(Plane3<T> p[6]) const
{
    //
    //        Plane order: Top, Right, Bottom, Left, Near, Far.
    //  Normals point outwards.
    //

if (! _orthographic)
    {
        Vec3<T> a( _left,  _bottom, -_nearPlane);
        Vec3<T> b( _left,  _top,    -_nearPlane);
        Vec3<T> c( _right, _top,    -_nearPlane);
        Vec3<T> d( _right, _bottom, -_nearPlane);
        Vec3<T> o(0,0,0);

p[0].set( o, c, b );
        p[1].set( o, d, c );
        p[2].set( o, a, d );
        p[3].set( o, b, a );
    }
    else
    {
        p[0].set( Vec3<T>( 0, 1, 0), _top );
        p[1].set( Vec3<T>( 1, 0, 0), _right );
        p[2].set( Vec3<T>( 0,-1, 0),-_bottom );
        p[3].set( Vec3<T>(-1, 0, 0),-_left );
    }
    p[4].set( Vec3<T>(0, 0, 1), -_nearPlane );
    p[5].set( Vec3<T>(0, 0,-1), _farPlane );
}

template<class T>
void Frustum<T>::planes(Plane3<T> p[6], const Matrix44<T> &M) const
{
    //
    //  Plane order: Top, Right, Bottom, Left, Near, Far.
    //  Normals point outwards.
    //

Vec3<T> a   = Vec3<T>( _left,  _bottom, -_nearPlane) * M;
    Vec3<T> b   = Vec3<T>( _left,  _top,    -_nearPlane) * M;
    Vec3<T> c   = Vec3<T>( _right, _top,    -_nearPlane) * M;
    Vec3<T> d   = Vec3<T>( _right, _bottom, -_nearPlane) * M;
    if (! _orthographic)
    {
        double s    = _farPlane / double(_nearPlane);
        T farLeft   = (T) (s * _left);
        T farRight  = (T) (s * _right);
        T farTop    = (T) (s * _top);
        T farBottom = (T) (s * _bottom);
        Vec3<T> e   = Vec3<T>( farLeft,  farBottom, -_farPlane) * M;
        Vec3<T> f   = Vec3<T>( farLeft,  farTop,    -_farPlane) * M;
        Vec3<T> g   = Vec3<T>( farRight, farTop,    -_farPlane) * M;
        Vec3<T> o   = Vec3<T>(0,0,0) * M;
        p[0].set( o, c, b );
        p[1].set( o, d, c );
        p[2].set( o, a, d );
        p[3].set( o, b, a );
        p[4].set( a, d, c );
        p[5].set( e, f, g );
     }
    else
    {
        Vec3<T> e   = Vec3<T>( _left,  _bottom, -_farPlane) * M;
        Vec3<T> f   = Vec3<T>( _left,  _top,    -_farPlane) * M;
        Vec3<T> g   = Vec3<T>( _right, _top,    -_farPlane) * M;
        Vec3<T> h   = Vec3<T>( _right, _bottom, -_farPlane) * M;
        p[0].set( c, g, f );
        p[1].set( d, h, g );
        p[2].set( a, e, h );
        p[3].set( b, f, e );
        p[4].set( a, d, c );
        p[5].set( e, f, g );
    }
}

typedef Frustum<float>  Frustumf;
typedef Frustum<double> Frustumd;

IMATH_INTERNAL_NAMESPACE_HEADER_EXIT

#if defined _WIN32 || defined _WIN64
    #ifdef _redef_near
        #define near
    #endif
    #ifdef _redef_far
        #define far
    #endif
#endif

#endif // INCLUDED_IMATHFRUSTUM_H

MR SKB