tween.hpp

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/*
 * Copyright (C) 2023  Christopher J. Howard
 *
 * This file is part of Antkeeper source code.
 *
 * Antkeeper source code is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * Antkeeper source code is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with Antkeeper source code.  If not, see <http://www.gnu.org/licenses/>.
 */
 
#ifndef ANTKEEPER_TWEEN_HPP
#define ANTKEEPER_TWEEN_HPP
 
#include <algorithm>
#include <functional>
#include <stdexcept>
#include <type_traits>
 
template <class T, class S = float>
class tween
{
public:
    static_assert(std::is_scalar<S>::value);
    
    typedef T value_type;
    typedef S scalar_type;
    typedef typename std::decay<std::function<value_type(const value_type&, const value_type&, scalar_type)>>::type interpolator_type;
    
private:
    static value_type interpolator_error(const value_type&, const value_type&, scalar_type);
    
public:
    
    tween(const value_type& state0, const value_type& state1, interpolator_type interpolator = tween<T, S>::interpolator_error);
    
    explicit tween(const value_type& value, interpolator_type interpolator = tween<T, S>::interpolator_error);
    
    tween();
 
    const value_type& operator[](int i) const;
 
    value_type& operator[](int i);
    
    value_type operator[](scalar_type a) const;
 
    value_type interpolate(scalar_type a) const;
    
    void set_interpolator(const interpolator_type& interpolator);
 
    const interpolator_type& get_interpolator() const;
 
    void update();
 
    void swap();
 
private:
    value_type states[2];
    interpolator_type interpolator;
};
 
template <class T, class S>
typename tween<T, S>::value_type tween<T, S>::interpolator_error(const value_type&, const value_type&, scalar_type)
{
    throw std::runtime_error("tween interpolator not set");
}
 
template <class T, class S>
tween<T, S>::tween(const value_type& value, interpolator_type interpolator):
    states{value, value},
    interpolator(interpolator)
{}
 
template <class T, class S>
tween<T, S>::tween(const value_type& state0, const value_type& state1, interpolator_type interpolator):
    states{state0, state1},
    interpolator(interpolator)
{}
 
template <class T, class S>
tween<T, S>::tween():
    interpolator(nullptr)
{}
 
template <class T, class S>
inline const typename tween<T, S>::value_type& tween<T, S>::operator[](int i) const
{
    return states[i];
}
 
template <class T, class S>
inline typename tween<T, S>::value_type& tween<T, S>::operator[](int i)
{
    return states[i];
}
 
template <class T, class S>
inline typename tween<T, S>::value_type tween<T, S>::operator[](scalar_type a) const
{
    return interpolate(a);
}
 
template <class T, class S>
inline typename tween<T, S>::value_type tween<T, S>::interpolate(scalar_type a) const
{
    return interpolator(states[0], states[1], a);
}
 
template <class T, class S>
inline void tween<T, S>::set_interpolator(const interpolator_type& interpolator)
{
    this->interpolator = interpolator;
}
 
template <class T, class S>
inline const typename tween<T, S>::interpolator_type& tween<T, S>::get_interpolator() const
{
    return interpolator;
}
 
template <class T, class S>
inline void tween<T, S>::update()
{
    states[0] = states[1];
}
 
template <class T, class S>
inline void tween<T, S>::swap()
{
    std::swap(states[0], states[1]);
}
 
#endif // ANTKEEPER_TWEEN_HPP