LinearInterpolator.h

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#pragma once

#include "IInterpolator.h"

#include <assert.h>


template< typename KeyType >
class LinearInterpolator : public IInterpolator< KeyType >
{
private:
protected:
public:
    explicit        LinearInterpolator      () = default;
    explicit        LinearInterpolator      ( const Key< KeyType >& leftKey,
                                              const Key< KeyType >& rightKey,
                                              UPtr< const IInterpolator< KeyType > >& leftInterpolator,
                                              UPtr< const IInterpolator< KeyType > >& rightInterpolator );
                    ~LinearInterpolator     () = default;


    virtual KeyType         Interpolate     ( TimeType time, Key< KeyType >& left, Key< KeyType >& right ) override;

    virtual void            Update          ( const Key< KeyType >& leftKey,
                                              const Key< KeyType >& rightKey,
                                              UPtr< const IInterpolator< KeyType > >& leftInterpolator,
                                              UPtr< const IInterpolator< KeyType > >& rightInterpolator ) override;

    virtual KeyType         LeftTangent     ( const Key< KeyType >& left, const Key< KeyType >& right ) const override;
    virtual KeyType         RightTangent    ( const Key< KeyType >& left, const Key< KeyType >& right ) const override;

protected:
    KeyType             Tangent     ( const Key< KeyType >& left, const Key< KeyType >& right ) const;
};

//====================================================================================//
//          Implementation  
//====================================================================================//


// ================================ //
//
template< typename KeyType >
inline              LinearInterpolator< KeyType >::LinearInterpolator   ( const Key< KeyType >& leftKey,
                                                                          const Key< KeyType >& rightKey,
                                                                          UPtr< const IInterpolator< KeyType > >& leftInterpolator,
                                                                          UPtr< const IInterpolator< KeyType >> & rightInterpolator )
{}

// ================================ //
//
template< typename KeyType >
inline KeyType      LinearInterpolator< KeyType >::Interpolate  ( TimeType time, Key< KeyType >& left, Key< KeyType >& right )
{
    TimeType timeInterval = right.Time - left.Time;
    TimeType progress = ( time - left.Time ) / timeInterval;

    auto leftResult = ( 1.0 + (-1.0f) * progress ) * left.Value;    // Multiply by -1.0f to avoid calling operator-
    auto rightResult = progress * right.Value;

    return static_cast< KeyType >( leftResult + rightResult );
}

// ================================ //
//
template< typename KeyType >
inline void         LinearInterpolator< KeyType >::Update       ( const Key< KeyType >& leftKey,
                                                                  const Key< KeyType >& rightKey,
                                                                  UPtr< const IInterpolator< KeyType > >& leftInterpolator,
                                                                  UPtr< const IInterpolator< KeyType > >& rightInterpolator )
{
    // Intencionally empty.
}

// ================================ //
//
template< typename KeyType >
inline KeyType      LinearInterpolator< KeyType >::LeftTangent  ( const Key< KeyType >& left, const Key< KeyType >& right ) const
{
    return Tangent( left, right );
}

// ================================ //
//
template< typename KeyType >
inline KeyType      LinearInterpolator< KeyType >::RightTangent ( const Key< KeyType >& left, const Key< KeyType >& right ) const
{
    return Tangent( left, right );
}


//====================================================================================//
//          Internal    
//====================================================================================//

// ================================ //
//
template< typename KeyType >
inline KeyType      LinearInterpolator< KeyType >::Tangent      ( const Key< KeyType >& left, const Key< KeyType >& right ) const
{
    KeyType valueInterval = right.Value - left.Value;
    TimeType timeInterval = right.Time - left.Time;

    return static_cast< KeyType >( ( TimeType( 1.0f ) / timeInterval )* valueInterval );
}